Release v1.2.2

Fix scroll tracking bugs

Examples/Maps/Maps/ViewController.swift

@@ -26,8 +26,8 @@ class ViewController: UIViewController, MKMapViewDelegate, UISearchBarDelegate,
 
         searchVC = storyboard?.instantiateViewController(withIdentifier: "SearchPanel") as? SearchPanelViewController
 
-        // Add a content view controller
-        fpc.show(searchVC, sender: self)
+        // Set a content view controller
+        fpc.set(contentViewController: searchVC)
         fpc.track(scrollView: searchVC.tableView)
 
         setupMapView()
@@ -234,6 +234,10 @@ public class SearchPanelLandscapeLayout: FloatingPanelLayout {
             ]
         }
     }
+
+    public func backdropAlphaFor(position: FloatingPanelPosition) -> CGFloat {
+        return 0.0
+    }
 }
 
 class SearchCell: UITableViewCell {

Examples/Samples/Sources/Base.lproj/Main.storyboard

@@ -1,11 +1,11 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="14313.18" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES" useSafeAreas="YES" colorMatched="YES" initialViewController="RoN-h0-uBD">
+<document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="14460.31" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES" useSafeAreas="YES" colorMatched="YES" initialViewController="RoN-h0-uBD">
     <device id="retina4_7" orientation="portrait">
         <adaptation id="fullscreen"/>
     </device>
     <dependencies>
         <deployment identifier="iOS"/>
-        <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="14283.14"/>
+        <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="14460.20"/>
         <capability name="Safe area layout guides" minToolsVersion="9.0"/>
         <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
     </dependencies>
@@ -190,7 +190,7 @@
                                 </connections>
                             </button>
                             <stackView opaque="NO" contentMode="scaleToFill" axis="vertical" alignment="top" spacing="44" translatesAutoresizingMaskIntoConstraints="NO" id="9p4-06-y2T">
-                                <rect key="frame" x="145" y="108" width="85" height="178"/>
+                                <rect key="frame" x="139.5" y="108" width="96" height="252"/>
                                 <subviews>
                                     <button opaque="NO" contentMode="scaleToFill" contentHorizontalAlignment="center" contentVerticalAlignment="center" buttonType="roundedRect" lineBreakMode="middleTruncation" translatesAutoresizingMaskIntoConstraints="NO" id="i9x-x5-n1q">
                                         <rect key="frame" x="0.0" y="0.0" width="80" height="30"/>
@@ -213,6 +213,13 @@
                                             <action selector="moveToTipWithSender:" destination="bYI-y3-Rzb" eventType="touchUpInside" id="BmL-91-9ai"/>
                                         </connections>
                                     </button>
+                                    <button opaque="NO" contentMode="scaleToFill" contentHorizontalAlignment="center" contentVerticalAlignment="center" buttonType="roundedRect" lineBreakMode="middleTruncation" translatesAutoresizingMaskIntoConstraints="NO" id="szf-HE-QTk">
+                                        <rect key="frame" x="0.0" y="222" width="96" height="30"/>
+                                        <state key="normal" title="Update layout"/>
+                                        <connections>
+                                            <action selector="updateLayout:" destination="bYI-y3-Rzb" eventType="touchUpInside" id="Woz-a7-YMJ"/>
+                                        </connections>
+                                    </button>
                                 </subviews>
                             </stackView>
                         </subviews>
@@ -356,7 +363,7 @@
                     </connections>
                 </swipeGestureRecognizer>
             </objects>
-            <point key="canvasLocation" x="1239" y="806"/>
+            <point key="canvasLocation" x="1311" y="806"/>
         </scene>
         <!--Detail View Controller-->
         <scene sceneID="b6k-zi-3wn">
@@ -390,14 +397,36 @@
                                     <constraint firstAttribute="height" constant="44" id="DQJ-cY-cKx"/>
                                 </constraints>
                             </view>
+                            <stackView opaque="NO" contentMode="scaleToFill" axis="vertical" spacing="22" translatesAutoresizingMaskIntoConstraints="NO" id="tP3-oJ-4EB">
+                                <rect key="frame" x="130.5" y="108" width="114" height="82"/>
+                                <subviews>
+                                    <button opaque="NO" contentMode="scaleToFill" contentHorizontalAlignment="center" contentVerticalAlignment="center" buttonType="roundedRect" lineBreakMode="middleTruncation" translatesAutoresizingMaskIntoConstraints="NO" id="c5r-jU-haj">
+                                        <rect key="frame" x="0.0" y="0.0" width="114" height="30"/>
+                                        <state key="normal" title="Show"/>
+                                        <connections>
+                                            <action selector="buttonPressed:" destination="YC8-ae-15L" eventType="touchUpInside" id="Mi1-o6-TWt"/>
+                                        </connections>
+                                    </button>
+                                    <button opaque="NO" contentMode="scaleToFill" contentHorizontalAlignment="center" contentVerticalAlignment="center" buttonType="roundedRect" lineBreakMode="middleTruncation" translatesAutoresizingMaskIntoConstraints="NO" id="wmd-ab-Nz3">
+                                        <rect key="frame" x="0.0" y="52" width="114" height="30"/>
+                                        <state key="normal" title="Present Modallly"/>
+                                        <connections>
+                                            <action selector="buttonPressed:" destination="YC8-ae-15L" eventType="touchUpInside" id="tjH-Ev-kpx"/>
+                                            <segue destination="bYI-y3-Rzb" kind="presentation" identifier="PresentModallySegue" id="3yq-HE-Tgn"/>
+                                        </connections>
+                                    </button>
+                                </subviews>
+                            </stackView>
                         </subviews>
                         <color key="backgroundColor" white="1" alpha="1" colorSpace="custom" customColorSpace="genericGamma22GrayColorSpace"/>
                         <gestureRecognizers/>
                         <constraints>
                             <constraint firstItem="noi-1a-5bZ" firstAttribute="top" secondItem="g7l-kO-y7q" secondAttribute="top" constant="12" id="EQy-cr-F2Y"/>
+                            <constraint firstItem="tP3-oJ-4EB" firstAttribute="centerX" secondItem="g7l-kO-y7q" secondAttribute="centerX" id="EsD-Vf-dNZ"/>
                             <constraint firstItem="8yw-OC-Ubk" firstAttribute="bottom" secondItem="g7l-kO-y7q" secondAttribute="bottom" id="JOL-wC-w74"/>
                             <constraint firstItem="8yw-OC-Ubk" firstAttribute="leading" secondItem="tAi-nk-rDB" secondAttribute="leading" id="RiJ-Hb-OOZ"/>
                             <constraint firstItem="8yw-OC-Ubk" firstAttribute="trailing" secondItem="tAi-nk-rDB" secondAttribute="trailing" id="Sof-yL-mwK"/>
+                            <constraint firstItem="tP3-oJ-4EB" firstAttribute="top" secondItem="tAi-nk-rDB" secondAttribute="top" constant="88" id="Zhb-Ss-epe"/>
                             <constraint firstItem="Kva-Z7-0qY" firstAttribute="trailing" secondItem="tAi-nk-rDB" secondAttribute="trailing" id="kkp-Yo-FQW"/>
                             <constraint firstItem="tAi-nk-rDB" firstAttribute="trailing" secondItem="noi-1a-5bZ" secondAttribute="trailing" constant="12" id="lv9-Nf-HNB"/>
                             <constraint firstItem="Kva-Z7-0qY" firstAttribute="leading" secondItem="tAi-nk-rDB" secondAttribute="leading" id="oVC-i1-TwS"/>
@@ -413,6 +442,7 @@
                     <size key="freeformSize" width="375" height="778"/>
                     <connections>
                         <outlet property="closeButton" destination="noi-1a-5bZ" id="eWQ-ha-8y7"/>
+                        <segue destination="bYI-y3-Rzb" kind="show" identifier="ShowSegue" id="r1P-2i-NDe"/>
                     </connections>
                 </viewController>
                 <placeholder placeholderIdentifier="IBFirstResponder" id="Wqk-xl-O3I" userLabel="First Responder" sceneMemberID="firstResponder"/>
@@ -432,7 +462,7 @@
                     </connections>
                 </pongPressGestureRecognizer>
             </objects>
-            <point key="canvasLocation" x="1442" y="-23"/>
+            <point key="canvasLocation" x="1440.8" y="-23.388305847076463"/>
         </scene>
         <!--Debug Text View Controller-->
         <scene sceneID="Bkq-O7-q4A">
@@ -507,4 +537,7 @@ Section 1.10.33 of "de Finibus Bonorum et Malorum", written by Cicero in 45 BC
             <point key="canvasLocation" x="729" y="-23"/>
         </scene>
     </scenes>
+    <inferredMetricsTieBreakers>
+        <segue reference="3yq-HE-Tgn"/>
+    </inferredMetricsTieBreakers>
 </document>

Examples/Samples/Sources/ViewController.swift

@@ -9,7 +9,7 @@
 import UIKit
 import FloatingPanel
 
-class SampleListViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
+class SampleListViewController: UIViewController, UITableViewDataSource, UITableViewDelegate, FloatingPanelControllerDelegate, FloatingPanelLayout {
     @IBOutlet weak var tableView: UITableView!
 
     enum Menu: Int, CaseIterable {
@@ -19,15 +19,17 @@ class SampleListViewController: UIViewController, UITableViewDataSource, UITable
         case showModal
         case showTabBar
         case showNestedScrollView
+        case showRemovablePanel
 
         var name: String {
             switch self {
-            case .trackingTableView: return "Scroll tracking (UITableView)"
-            case .trackingTextView: return "Scroll tracking (UITextView)"
+            case .trackingTableView: return "Scroll tracking(TableView)"
+            case .trackingTextView: return "Scroll tracking(TextView)"
             case .showDetail: return "Show Detail Panel"
             case .showModal: return "Show Modal"
             case .showTabBar: return "Show Tab Bar"
             case .showNestedScrollView: return "Show Nested ScrollView"
+            case .showRemovablePanel: return "Show Removable Panel"
             }
         }
 
@@ -39,12 +41,14 @@ class SampleListViewController: UIViewController, UITableViewDataSource, UITable
             case .showModal: return "ModalViewController"
             case .showTabBar: return "TabBarViewController"
             case .showNestedScrollView: return "NestedScrollViewController"
+            case .showRemovablePanel: return "DetailViewController"
             }
         }
     }
 
     var mainPanelVC: FloatingPanelController!
     var detailPanelVC: FloatingPanelController!
+    var currentMenu: Menu = .trackingTableView
 
     override func viewDidLoad() {
         super.viewDidLoad()
@@ -52,21 +56,28 @@ class SampleListViewController: UIViewController, UITableViewDataSource, UITable
         tableView.delegate = self
         tableView.register(UITableViewCell.self, forCellReuseIdentifier: "Cell")
 
-        let contentVC = DebugTableViewController(style: .plain)
+        let contentVC = DebugTableViewController()
         addMainPanel(with: contentVC)
     }
 
+    override func viewDidAppear(_ animated: Bool) {
+        super.viewDidAppear(animated)
+    }
+
     func addMainPanel(with contentVC: UIViewController) {
         // Initialize FloatingPanelController
         mainPanelVC = FloatingPanelController()
+        mainPanelVC.delegate = self
+        mainPanelVC.isRemovalInteractionEnabled = (currentMenu == .showRemovablePanel)
 
         // Initialize FloatingPanelController and add the view
         mainPanelVC.surfaceView.cornerRadius = 6.0
         mainPanelVC.surfaceView.shadowHidden = false
 
-        // Add a content view controller and connect with the scroll view
-        mainPanelVC.show(contentVC, sender: self)
+        // Set a content view controller
+        mainPanelVC.set(contentViewController: contentVC)
 
+        // Track a scroll view
         switch contentVC {
         case let consoleVC as DebugTextViewController:
             mainPanelVC.track(scrollView: consoleVC.textView)
@@ -104,11 +115,13 @@ class SampleListViewController: UIViewController, UITableViewDataSource, UITable
     func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
         let menu = Menu.allCases[indexPath.row]
         let contentVC: UIViewController = {
-            guard let storyboardID = menu.storyboardID else { return DebugTableViewController(style: .plain) }
+            guard let storyboardID = menu.storyboardID else { return DebugTableViewController() }
             guard let vc = self.storyboard?.instantiateViewController(withIdentifier: storyboardID) else { fatalError() }
             return vc
         }()
 
+        self.currentMenu = menu
+
         switch menu {
         case .showDetail:
             detailPanelVC?.removeFromParent()
@@ -120,10 +133,8 @@ class SampleListViewController: UIViewController, UITableViewDataSource, UITable
             detailPanelVC.surfaceView.cornerRadius = 6.0
             detailPanelVC.surfaceView.shadowHidden = false
 
-            // Add a content view controller and connect with the scroll view
-            detailPanelVC.show(contentVC, sender: self)
-
-            // (contentVC as? DetailViewController)?.closeButton?.addTarget(self, action: #selector(dismissDetailPanelVC), for: .touchUpInside)
+            // Set a content view controller
+            detailPanelVC.set(contentViewController: contentVC)
 
             //  Add FloatingPanel to self.view
             detailPanelVC.addPanel(toParent: self, belowView: nil, animated: true)
@@ -137,6 +148,71 @@ class SampleListViewController: UIViewController, UITableViewDataSource, UITable
             }
         }
     }
+
+    func floatingPanel(_ vc: FloatingPanelController, layoutFor newCollection: UITraitCollection) -> FloatingPanelLayout? {
+        if currentMenu == .showRemovablePanel {
+            return newCollection.verticalSizeClass == .compact ? RemovablePanelLandscapeLayout() :  RemovablePanelLayout()
+        } else {
+            return self
+        }
+    }
+
+    var initialPosition: FloatingPanelPosition {
+        return .half
+    }
+
+    func insetFor(position: FloatingPanelPosition) -> CGFloat? {
+        switch position {
+        case .full: return UIScreen.main.bounds.height == 667.0 ? 18.0 : 16.0
+        case .half: return 262.0
+        case .tip: return 69.0
+        }
+    }
+}
+
+class RemovablePanelLayout: FloatingPanelLayout {
+    var initialPosition: FloatingPanelPosition {
+        return .half
+    }
+    var supportedPositions: Set<FloatingPanelPosition> {
+        return [.full, .half]
+    }
+    var bottomInteractionBuffer: CGFloat {
+        return 261.0 - 22.0
+    }
+
+    func insetFor(position: FloatingPanelPosition) -> CGFloat? {
+        switch position {
+        case .full: return 16.0
+        case .half: return 261.0
+        default: return nil
+        }
+    }
+    func backdropAlphaFor(position: FloatingPanelPosition) -> CGFloat {
+        return 0.3
+    }
+}
+
+class RemovablePanelLandscapeLayout: FloatingPanelLayout {
+    var initialPosition: FloatingPanelPosition {
+        return .half
+    }
+    var supportedPositions: Set<FloatingPanelPosition> {
+        return [.half]
+    }
+    var bottomInteractionBuffer: CGFloat {
+        return 261.0 - 22.0
+    }
+
+    func insetFor(position: FloatingPanelPosition) -> CGFloat? {
+        switch position {
+        case .half: return 261.0
+        default: return nil
+        }
+    }
+    func backdropAlphaFor(position: FloatingPanelPosition) -> CGFloat {
+        return 0.3
+    }
 }
 
 class NestedScrollViewController: UIViewController {
@@ -179,16 +255,98 @@ class DebugTextViewController: UIViewController, UITextViewDelegate {
     }
 }
 
-class DebugTableViewController: UITableViewController {
+class DebugTableViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
+    weak var tableView: UITableView!
     var items: [String] = []
+    var itemHeight: CGFloat = 66.0
     override func viewDidLoad() {
         super.viewDidLoad()
+
+        let tableView = UITableView(frame: .zero,
+                                    style: .plain)
+        view.addSubview(tableView)
+        tableView.translatesAutoresizingMaskIntoConstraints = false
+        NSLayoutConstraint.activate([
+            tableView.topAnchor.constraint(equalTo: view.topAnchor),
+            tableView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
+            tableView.leftAnchor.constraint(equalTo: view.leftAnchor),
+            tableView.rightAnchor.constraint(equalTo: view.rightAnchor)
+            ])
+        tableView.dataSource = self
+        tableView.delegate = self
+        self.tableView = tableView
+
+        let stackView = UIStackView()
+        view.addSubview(stackView)
+        stackView.axis = .vertical
+        stackView.distribution = .fillEqually
+        stackView.alignment = .trailing
+        stackView.spacing = 10.0
+        stackView.translatesAutoresizingMaskIntoConstraints = false
+        NSLayoutConstraint.activate([
+            stackView.topAnchor.constraint(equalTo: view.topAnchor, constant: 22.0),
+            stackView.rightAnchor.constraint(equalTo: view.rightAnchor, constant: -22.0),
+            ])
+
+        let button = UIButton()
+        button.setTitle("Animate Scroll", for: .normal)
+        button.setTitleColor(view.tintColor, for: .normal)
+        button.addTarget(self, action: #selector(animateScroll), for: .touchUpInside)
+        stackView.addArrangedSubview(button)
+
+        let button2 = UIButton()
+        button2.setTitle("Change content size", for: .normal)
+        button2.setTitleColor(view.tintColor, for: .normal)
+        button2.addTarget(self, action: #selector(changeContentSize), for: .touchUpInside)
+        stackView.addArrangedSubview(button2)
+
         for i in 0...100 {
             items.append("Items \(i)")
         }
         tableView.register(UITableViewCell.self, forCellReuseIdentifier: "Cell")
     }
 
+    @objc func animateScroll() {
+        tableView.scrollToRow(at: IndexPath(row: lround(Double(items.count) / 2.0),
+                                            section: 0),
+                              at: .top, animated: true)
+    }
+
+    @objc func changeContentSize() {
+        let actionSheet = UIAlertController(title: "Change content size", message: "", preferredStyle: .actionSheet)
+        actionSheet.addAction(UIAlertAction(title: "Large", style: .default, handler: { (_) in
+            self.itemHeight = 66.0
+            self.changeItems(100)
+        }))
+        actionSheet.addAction(UIAlertAction(title: "Match", style: .default, handler: { (_) in
+            switch self.tableView.bounds.height {
+            case 585: // iPhone 6,7,8
+                self.itemHeight = self.tableView.bounds.height / 13.0
+                self.changeItems(13)
+            case 656: // iPhone {6,7,8} Plus
+                self.itemHeight = self.tableView.bounds.height / 16.0
+                self.changeItems(16)
+            default: // iPhone X family
+                self.itemHeight = self.tableView.bounds.height / 12.0
+                self.changeItems(12)
+            }
+        }))
+        actionSheet.addAction(UIAlertAction(title: "Short", style: .default, handler: { (_) in
+            self.itemHeight = 66.0
+            self.changeItems(3)
+        }))
+
+        self.present(actionSheet, animated: true, completion: nil)
+    }
+
+    func changeItems(_ count: Int) {
+        items.removeAll()
+        for i in 0..<count {
+            items.append("Items \(i)")
+        }
+        tableView.reloadData()
+    }
+
     @objc func close(sender: UIButton) {
         //  Remove FloatingPanel from a view
         (self.parent as! FloatingPanelController).removePanelFromParent(animated: true, completion: nil)
@@ -238,19 +396,28 @@ class DebugTableViewController: UITableViewController {
         print("Content View: willTransition(to: \(newCollection), with: \(coordinator))")
     }
 
-    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
+    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
         return items.count
     }
 
-    override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
-        return 66.0
+    func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
+        return itemHeight
     }
 
-    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
+    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
         let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)
         cell.textLabel?.text = items[indexPath.row]
         return cell
     }
+
+    func tableView(_ tableView: UITableView, editActionsForRowAt indexPath: IndexPath) -> [UITableViewRowAction]? {
+        return [
+            UITableViewRowAction(style: .destructive, title: "Delete", handler: { (action, path) in
+                self.items.remove(at: path.row)
+                tableView.deleteRows(at: [path], with: .automatic)
+            }),
+        ]
+    }
 }
 
 class DetailViewController: UIViewController {
@@ -260,6 +427,18 @@ class DetailViewController: UIViewController {
         // dismiss(animated: true, completion: nil)
         (self.parent as? FloatingPanelController)?.removePanelFromParent(animated: true, completion: nil)
     }
+
+    @IBAction func buttonPressed(_ sender: UIButton) {
+        switch sender.titleLabel?.text {
+        case "Show":
+            performSegue(withIdentifier: "ShowSegue", sender: self)
+        case "Present Modally":
+            performSegue(withIdentifier: "PresentModallySegue", sender: self)
+        default:
+            break
+        }
+    }
+
     @IBAction func tapped(_ sender: Any) {
         print("Detail panel is tapped!")
     }
@@ -271,25 +450,31 @@ class DetailViewController: UIViewController {
     }
 }
 
-class ModalViewController: UIViewController {
+class ModalViewController: UIViewController, FloatingPanelControllerDelegate {
     var fpc: FloatingPanelController!
     var consoleVC: DebugTextViewController!
+
     @IBOutlet weak var safeAreaView: UIView!
+
+    var isNewlayout: Bool = false
+
     override func viewWillAppear(_ animated: Bool) {
         super.viewWillAppear(animated)
         // Initialize FloatingPanelController
         fpc = FloatingPanelController()
+        fpc.delegate = self
 
         // Initialize FloatingPanelController and add the view
         fpc.surfaceView.cornerRadius = 6.0
         fpc.surfaceView.shadowHidden = false
 
-        // Add a content view controller and connect with the scroll view
+        // Set a content view controller and track the scroll view
         let consoleVC = storyboard?.instantiateViewController(withIdentifier: "ConsoleViewController") as! DebugTextViewController
-        fpc.show(consoleVC, sender: self)
-        self.consoleVC = consoleVC
+        fpc.set(contentViewController: consoleVC)
         fpc.track(scrollView: consoleVC.textView)
 
+        self.consoleVC = consoleVC
+
         //  Add FloatingPanel to self.view
         fpc.addPanel(toParent: self, belowView: safeAreaView)
     }
@@ -313,6 +498,31 @@ class ModalViewController: UIViewController {
     @IBAction func moveToTip(sender: UIButton) {
         fpc.move(to: .tip, animated: true)
     }
+
+    @IBAction func updateLayout(_ sender: Any) {
+        isNewlayout = !isNewlayout
+        UIView.animate(withDuration: 0.5) {
+            self.fpc.updateLayout()
+        }
+    }
+
+    func floatingPanel(_ vc: FloatingPanelController, layoutFor newCollection: UITraitCollection) -> FloatingPanelLayout? {
+        return (isNewlayout) ? ModalSecondLayout() : nil
+    }
+}
+
+class ModalSecondLayout: FloatingPanelLayout {
+    var initialPosition: FloatingPanelPosition {
+        return .half
+    }
+
+    func insetFor(position: FloatingPanelPosition) -> CGFloat? {
+        switch position {
+        case .full: return 18.0
+        case .half: return 262.0
+        case .tip: return 44.0
+        }
+    }
 }
 
 class TabBarViewController: UITabBarController {}
@@ -331,11 +541,11 @@ class TabBarContentViewController: UIViewController, FloatingPanelControllerDele
         fpc.surfaceView.cornerRadius = 6.0
         fpc.surfaceView.shadowHidden = false
 
-        // Add a content view controller and connect with the scroll view
+        // Set a content view controller and track the scroll view
         let consoleVC = storyboard?.instantiateViewController(withIdentifier: "ConsoleViewController") as! DebugTextViewController
-        fpc.show(consoleVC, sender: self)
-        self.consoleVC = consoleVC
+        fpc.set(contentViewController: consoleVC)
         fpc.track(scrollView: consoleVC.textView)
+        self.consoleVC = consoleVC
 
         //  Add FloatingPanel to self.view
         fpc.addPanel(toParent: self)

Examples/Stocks/Stocks/Base.lproj/Main.storyboard

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="14313.18" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES" useSafeAreas="YES" colorMatched="YES" initialViewController="BYZ-38-t0r">
-    <device id="retina5_9" orientation="portrait">
+    <device id="retina4_7" orientation="portrait">
         <adaptation id="fullscreen"/>
     </device>
     <dependencies>
@@ -15,11 +15,11 @@
             <objects>
                 <viewController id="BYZ-38-t0r" customClass="ViewController" customModule="Stocks" customModuleProvider="target" sceneMemberID="viewController">
                     <view key="view" contentMode="scaleToFill" id="8bC-Xf-vdC">
-                        <rect key="frame" x="0.0" y="0.0" width="375" height="812"/>
+                        <rect key="frame" x="0.0" y="0.0" width="375" height="667"/>
                         <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>
                         <subviews>
                             <scrollView clipsSubviews="YES" multipleTouchEnabled="YES" contentMode="scaleToFill" translatesAutoresizingMaskIntoConstraints="NO" id="Uop-sw-I6p">
-                                <rect key="frame" x="0.0" y="109" width="375" height="624.66666666666663"/>
+                                <rect key="frame" x="0.0" y="85" width="375" height="537.5"/>
                                 <subviews>
                                     <imageView userInteractionEnabled="NO" contentMode="scaleToFill" horizontalHuggingPriority="251" verticalHuggingPriority="251" placeholderIntrinsicWidth="375" placeholderIntrinsicHeight="625" image="stocks_list" translatesAutoresizingMaskIntoConstraints="NO" id="XJR-iK-fem">
                                         <rect key="frame" x="0.0" y="0.0" width="375" height="625"/>
@@ -34,10 +34,10 @@
                                 </constraints>
                             </scrollView>
                             <view contentMode="scaleToFill" translatesAutoresizingMaskIntoConstraints="NO" id="dFl-81-6ok">
-                                <rect key="frame" x="0.0" y="733.66666666666663" width="375" height="78.333333333333371"/>
+                                <rect key="frame" x="0.0" y="622.5" width="375" height="44.5"/>
                                 <subviews>
                                     <imageView userInteractionEnabled="NO" contentMode="scaleToFill" horizontalHuggingPriority="251" verticalHuggingPriority="251" image="yahoo_bottom_bar" translatesAutoresizingMaskIntoConstraints="NO" id="NKr-gS-mpx">
-                                        <rect key="frame" x="0.0" y="0.0" width="375" height="44.333333333333336"/>
+                                        <rect key="frame" x="0.0" y="0.0" width="375" height="44.5"/>
                                         <color key="backgroundColor" white="0.0" alpha="0.0" colorSpace="custom" customColorSpace="genericGamma22GrayColorSpace"/>
                                         <constraints>
                                             <constraint firstAttribute="height" relation="greaterThanOrEqual" constant="44.5" id="B5t-ZF-qUj"/>
@@ -52,18 +52,17 @@
                                     <constraint firstItem="NKr-gS-mpx" firstAttribute="leading" secondItem="dFl-81-6ok" secondAttribute="leading" id="T2r-kY-JYy"/>
                                 </constraints>
                             </view>
-                            <stackView opaque="NO" contentMode="scaleToFill" fixedFrame="YES" axis="vertical" alignment="top" spacing="-8" translatesAutoresizingMaskIntoConstraints="NO" id="f7r-Al-pIN">
-                                <rect key="frame" x="16" y="44.000000000000014" width="153.33333333333334" height="56.666666666666664"/>
-                                <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMaxY="YES"/>
+                            <stackView opaque="NO" contentMode="scaleToFill" axis="vertical" alignment="top" spacing="-8" translatesAutoresizingMaskIntoConstraints="NO" id="f7r-Al-pIN">
+                                <rect key="frame" x="16" y="20" width="153.5" height="57"/>
                                 <subviews>
                                     <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="251" verticalHuggingPriority="251" text="STOCKS" textAlignment="natural" lineBreakMode="tailTruncation" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="PCG-Wl-fXa">
-                                        <rect key="frame" x="0.0" y="0.0" width="111.66666666666667" height="32.333333333333336"/>
+                                        <rect key="frame" x="0.0" y="0.0" width="111.5" height="32.5"/>
                                         <fontDescription key="fontDescription" type="system" weight="heavy" pointSize="27"/>
                                         <color key="textColor" white="1" alpha="1" colorSpace="custom" customColorSpace="genericGamma22GrayColorSpace"/>
                                         <nil key="highlightedColor"/>
                                     </label>
                                     <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="251" verticalHuggingPriority="251" text="OCTOBER 5" textAlignment="natural" lineBreakMode="tailTruncation" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="XmK-pu-9g4">
-                                        <rect key="frame" x="0.0" y="24.333333333333332" width="153.33333333333334" height="32.333333333333343"/>
+                                        <rect key="frame" x="0.0" y="24.5" width="153.5" height="32.5"/>
                                         <fontDescription key="fontDescription" type="system" weight="heavy" pointSize="27"/>
                                         <color key="textColor" red="0.55308091640472412" green="0.55657511949539185" blue="0.57255202531814575" alpha="1" colorSpace="custom" customColorSpace="displayP3"/>
                                         <nil key="highlightedColor"/>
@@ -75,10 +74,12 @@
                         <constraints>
                             <constraint firstItem="6Tk-OE-BBY" firstAttribute="trailing" secondItem="dFl-81-6ok" secondAttribute="trailing" id="20i-yz-AaQ"/>
                             <constraint firstItem="Uop-sw-I6p" firstAttribute="leading" secondItem="6Tk-OE-BBY" secondAttribute="leading" id="44w-r8-vYl"/>
+                            <constraint firstItem="f7r-Al-pIN" firstAttribute="leading" secondItem="6Tk-OE-BBY" secondAttribute="leading" constant="16" id="4Bq-Km-eET"/>
                             <constraint firstItem="Uop-sw-I6p" firstAttribute="top" secondItem="6Tk-OE-BBY" secondAttribute="top" constant="65" id="CXL-Dk-8MM"/>
                             <constraint firstItem="Uop-sw-I6p" firstAttribute="trailing" secondItem="6Tk-OE-BBY" secondAttribute="trailing" id="CsO-WF-T8L"/>
                             <constraint firstItem="dFl-81-6ok" firstAttribute="top" secondItem="Uop-sw-I6p" secondAttribute="bottom" id="Cz0-dW-r9H"/>
                             <constraint firstAttribute="bottom" secondItem="dFl-81-6ok" secondAttribute="bottom" id="KGl-8W-5ja"/>
+                            <constraint firstItem="f7r-Al-pIN" firstAttribute="top" secondItem="6Tk-OE-BBY" secondAttribute="top" constant="1.4210854715202004e-14" id="Qvt-vQ-PpT"/>
                             <constraint firstItem="dFl-81-6ok" firstAttribute="leading" secondItem="6Tk-OE-BBY" secondAttribute="leading" id="nlX-Ab-1aI"/>
                             <constraint firstItem="6Tk-OE-BBY" firstAttribute="bottom" secondItem="NKr-gS-mpx" secondAttribute="bottom" id="yeu-NH-Pmp"/>
                         </constraints>

Examples/Stocks/Stocks/ViewController.swift

@@ -34,8 +34,8 @@ class ViewController: UIViewController, FloatingPanelControllerDelegate {
 
         newsVC = storyboard?.instantiateViewController(withIdentifier: "News") as? NewsViewController
 
-        // Add a content view controller
-        fpc.show(newsVC, sender: self)
+        // Set a content view controller
+        fpc.set(contentViewController: newsVC)
         fpc.track(scrollView: newsVC.scrollView)
 
         fpc.addPanel(toParent: self, belowView: bottomToolView, animated: false)
@@ -117,7 +117,9 @@ class FloatingPanelStocksLayout: FloatingPanelLayout {
         }
     }
 
-    var backdropAlpha: CGFloat = 0.0
+    func backdropAlphaFor(position: FloatingPanelPosition) -> CGFloat {
+        return 0.0
+    }
 }
 
 // MARK: My custom behavior

FloatingPanel.podspec

@@ -1,10 +1,10 @@
 Pod::Spec.new do |s|
 
   s.name                = "FloatingPanel"
-  s.version             = "1.1.0"
-  s.summary             = "FloatingPanel is a simple and easy-to-use UI component of a floating panel interface"
+  s.version             = "1.2.2"
+  s.summary             = "FloatingPanel is a clean and easy-to-use UI component of a floating panel interface."
   s.description         = <<-DESC
-FloatingPanel is a simple and easy-to-use UI component for a new interface introduced in Apple Maps, Shortcuts and Stocks app.
+FloatingPanel is a clean and easy-to-use UI component for a new interface introduced in Apple Maps, Shortcuts and Stocks app.
 The new interface displays the related contents and utilities in parallel as a user wants.
                    DESC
   s.homepage            = "https://github.com/SCENEE/FloatingPanel"

Framework/Sources/FloatingPanel.swift

@@ -33,12 +33,21 @@ class FloatingPanel: NSObject, UIGestureRecognizerDelegate, UIScrollViewDelegate
 
     unowned let viewcontroller: FloatingPanelController
 
-    private(set) var state: FloatingPanelPosition = .tip
+    private(set) var state: FloatingPanelPosition = .tip {
+        didSet { viewcontroller.delegate?.floatingPanelDidChangePosition(viewcontroller) }
+    }
+
+    private var isBottomState: Bool {
+        let remains = layoutAdapter.layout.supportedPositions.filter { $0.rawValue > state.rawValue }
+        return remains.count == 0
+    }
 
     let panGesture: FloatingPanelPanGestureRecognizer
+    var isRemovalInteractionEnabled: Bool = false
 
     private var animator: UIViewPropertyAnimator?
     private var initialFrame: CGRect = .zero
+    private var initialScrollOffset: CGPoint = .zero
     private var transOffsetY: CGFloat = 0
     private var interactionInProgress: Bool = false
 
@@ -61,6 +70,8 @@ class FloatingPanel: NSObject, UIGestureRecognizerDelegate, UIScrollViewDelegate
                                                         layout: layout)
         self.behavior = behavior
 
+        state = layoutAdapter.layout.initialPosition
+
         panGesture = FloatingPanelPanGestureRecognizer()
 
         if #available(iOS 11.0, *) {
@@ -74,7 +85,7 @@ class FloatingPanel: NSObject, UIGestureRecognizerDelegate, UIScrollViewDelegate
         panGesture.delegate = self
     }
 
-    func layoutViews(in vc: UIViewController) {
+    func setUpViews(in vc: UIViewController) {
         unowned let view = vc.view!
 
         view.insertSubview(backdropView, belowSubview: surfaceView)
@@ -139,23 +150,24 @@ class FloatingPanel: NSObject, UIGestureRecognizerDelegate, UIScrollViewDelegate
 
     private func updateLayout(to target: FloatingPanelPosition?) {
         self.layoutAdapter.activateLayout(of: target)
-        self.setBackdropAlpha(of: target)
-    }
-
-    private func setBackdropAlpha(of target: FloatingPanelPosition?) {
-        switch target {
-        case .full?:
-            self.backdropView.alpha = layoutAdapter.layout.backdropAlpha
-        default:
-            self.backdropView.alpha = 0.0
-        }
     }
 
     private func getBackdropAlpha(with translation: CGPoint) -> CGFloat {
-        let topY = layoutAdapter.topY
-        let middleY = layoutAdapter.middleY
         let currentY = getCurrentY(from: initialFrame, with: translation)
-        return (1 - (currentY - topY) / (middleY - topY)) * layoutAdapter.layout.backdropAlpha
+
+        let next = directionalPosition(with: translation)
+        let pre = redirectionalPosition(with: translation)
+        let nextY = layoutAdapter.positionY(for: next)
+        let preY = layoutAdapter.positionY(for: pre)
+
+        let nextAlpha = layoutAdapter.layout.backdropAlphaFor(position: next)
+        let preAlpha = layoutAdapter.layout.backdropAlphaFor(position: pre)
+
+        if preY == nextY {
+            return preAlpha
+        } else {
+            return preAlpha + max(min(1.0, 1.0 - (nextY - currentY) / (nextY - preY) ), 0.0) * (nextAlpha - preAlpha)
+        }
     }
 
     // MARK: - UIGestureRecognizerDelegate
@@ -164,77 +176,155 @@ class FloatingPanel: NSObject, UIGestureRecognizerDelegate, UIScrollViewDelegate
                                   shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
         guard gestureRecognizer == panGesture else { return false }
 
-        log.debug("shouldRecognizeSimultaneouslyWith", otherGestureRecognizer)
+        /* log.debug("shouldRecognizeSimultaneouslyWith", otherGestureRecognizer) */
 
-        return otherGestureRecognizer == scrollView?.panGestureRecognizer
+        // all gestures of the tracking scroll view should be recognized in parallel
+        // and handle them in self.handle(panGesture:)
+        return scrollView?.gestureRecognizers?.contains(otherGestureRecognizer) ?? false
     }
 
     public func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldBeRequiredToFailBy otherGestureRecognizer: UIGestureRecognizer) -> Bool {
         guard gestureRecognizer == panGesture else { return false }
 
-        // Do not begin any gestures excluding the tracking scrollView's pan gesture until the pan gesture fails
-        if otherGestureRecognizer == scrollView?.panGestureRecognizer {
+        /* log.debug("shouldBeRequiredToFailBy", otherGestureRecognizer) */
+
+        // The tracking scroll view's gestures should begin without waiting for the pan gesture failure.
+        // `scrollView.gestureRecognizers` can contains the following gestures
+        // * UIScrollViewDelayedTouchesBeganGestureRecognizer
+        // * UIScrollViewPanGestureRecognizer (scrollView.panGestureRecognizer)
+        // * _UIDragAutoScrollGestureRecognizer
+        // * _UISwipeActionPanGestureRecognizer
+        // * UISwipeDismissalGestureRecognizer
+        if let scrollView = scrollView,
+            let scrollGestureRecognizers = scrollView.gestureRecognizers,
+            scrollGestureRecognizers.contains(otherGestureRecognizer) {
             return false
-        } else {
-            return true
         }
+
+        // Long press gesture should begin without waiting for the pan gesture failure.
+        if otherGestureRecognizer is UILongPressGestureRecognizer {
+            return false
+        }
+
+        // Do not begin any other gestures until the pan gesture fails.
+        return true
     }
 
     public func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRequireFailureOf otherGestureRecognizer: UIGestureRecognizer) -> Bool {
         guard gestureRecognizer == panGesture else { return false }
 
-        // Do not begin the pan gesture until any other gestures fail except fo the tracking scrollView's pan gesture.
+        log.debug("shouldRequireFailureOf", otherGestureRecognizer)
+
+        // Should begin the pan gesture without waiting for the tracking scroll view's gestures.
+        // `scrollView.gestureRecognizers` can contains the following gestures
+        // * UIScrollViewDelayedTouchesBeganGestureRecognizer
+        // * UIScrollViewPanGestureRecognizer (scrollView.panGestureRecognizer)
+        // * _UIDragAutoScrollGestureRecognizer
+        // * _UISwipeActionPanGestureRecognizer
+        // * UISwipeDismissalGestureRecognizer
+        if let scrollView = scrollView {
+            // On short contents scroll, `_UISwipeActionPanGestureRecognizer` blocks
+            // the panel's pan gesture if not returns false
+            if let scrollGestureRecognizers = scrollView.gestureRecognizers,
+                scrollGestureRecognizers.contains(otherGestureRecognizer) {
+                return false
+            }
+        }
+
         switch otherGestureRecognizer {
-        case scrollView?.panGestureRecognizer:
-            return false
         case is UIPanGestureRecognizer,
              is UISwipeGestureRecognizer,
              is UIRotationGestureRecognizer,
              is UIScreenEdgePanGestureRecognizer,
              is UIPinchGestureRecognizer:
+            // Do not begin the pan gesture until these gestures fail
             return true
         default:
+            // Should begin the pan gesture witout waiting tap/long press gestures fail
             return false
         }
     }
 
-    // MARK: - Gesture handling
+    var grabberAreaFrame: CGRect {
+        let grabberAreaFrame = CGRect(x: surfaceView.bounds.origin.x,
+                                     y: surfaceView.bounds.origin.y,
+                                     width: surfaceView.bounds.width,
+                                     height: FloatingPanelSurfaceView.topGrabberBarHeight * 2)
+        return grabberAreaFrame
+    }
 
+    // MARK: - Gesture handling
+    private let offsetThreshold: CGFloat = 5.0 // Optimal value from testing
     @objc func handle(panGesture: UIPanGestureRecognizer) {
         log.debug("Gesture >>>>", panGesture)
+        let velocity = panGesture.velocity(in: panGesture.view)
 
         switch panGesture {
         case scrollView?.panGestureRecognizer:
             guard let scrollView = scrollView else { return }
+
+            log.debug("SrollPanGesture ScrollView.contentOffset >>>", scrollView.contentOffset.y, scrollView.contentSize, scrollView.bounds.size)
+
+            // Prevent scoll slip by the top bounce when the scroll view's height is
+            // less than the content's height
+            if scrollView.isDecelerating == false, scrollView.contentSize.height > scrollView.bounds.height {
+                scrollView.bounces = (scrollView.contentOffset.y > offsetThreshold)
+            }
+
             if surfaceView.frame.minY > layoutAdapter.topY {
-                scrollView.contentOffset.y = scrollView.contentOffsetZero.y
+                switch state {
+                case .full:
+                    let point = panGesture.location(in: surfaceView)
+                    if grabberAreaFrame.contains(point) {
+                        // Preserve the current content offset in moving from full.
+                        scrollView.contentOffset.y = initialScrollOffset.y
+                    } else {
+                        // Prevent over scrolling in moving from full.
+                        scrollView.contentOffset.y = scrollView.contentOffsetZero.y
+                    }
+                case .half, .tip:
+                    guard scrollView.isDecelerating == false else {
+                        // Don't fix the scroll offset in animating the panel to half and tip.
+                        // It causes a buggy scrolling deceleration because `state` becomes
+                        // a target position in animating the panel on the interaction from full.
+                        return
+                    }
+                    // Fix the scroll offset in moving the panel from half and tip.
+                    scrollView.contentOffset.y = initialScrollOffset.y
+                }
+
+                // Always hide a scroll indicator at the non-top.
+                if interactionInProgress {
+                    lockScrollView()
+                }
+            } else {
+                // Always show a scroll indicator at the top.
+                if interactionInProgress {
+                    unlockScrollView()
+                }
             }
         case panGesture:
             let translation = panGesture.translation(in: panGesture.view!.superview)
-            let velocity = panGesture.velocity(in: panGesture.view)
             let location = panGesture.location(in: panGesture.view)
 
-            log.debug(panGesture.state, ">>>", "{ translation: \(translation), velocity: \(velocity) }")
+            log.debug(panGesture.state, ">>>", "translation: \(translation.y), velocity: \(velocity.y)")
 
-            if let scrollView = scrollView, scrollView.frame.contains(location) {
-                log.debug("ScrollView.contentOffset >>>", scrollView.contentOffset)
-                if state == .full {
-                    if scrollView.contentOffset.y - scrollView.contentOffsetZero.y > 0 {
-                        return
-                    }
-                    if scrollView.isDecelerating {
-                        return
-                    }
-                    if interactionInProgress == false, velocity.y < 0 || velocity.y > 2500.0 {
-                        return
-                    }
-                }
+            if shouldScrollViewHandleTouch(scrollView, point: location, velocity: velocity) {
+                return
+            }
+
+            if let animator = self.animator {
+                animator.stopAnimation(true)
+                self.animator = nil
             }
 
             switch panGesture.state {
             case .began:
                 panningBegan()
             case .changed:
+                if interactionInProgress == false {
+                    startInteraction(with: translation)
+                }
                 panningChange(with: translation)
             case .ended, .cancelled, .failed:
                 panningEnd(with: translation, velocity: velocity)
@@ -246,18 +336,56 @@ class FloatingPanel: NSObject, UIGestureRecognizerDelegate, UIScrollViewDelegate
         }
     }
 
+    private func shouldScrollViewHandleTouch(_ scrollView: UIScrollView?, point: CGPoint, velocity: CGPoint) -> Bool {
+        // When no scrollView, nothing to handle.
+        guard let scrollView = scrollView else { return false }
+
+        // For _UISwipeActionPanGestureRecognizer
+        if let scrollGestureRecognizers = scrollView.gestureRecognizers {
+            for gesture in scrollGestureRecognizers {
+                guard gesture.state == .began || gesture.state == .changed
+                else { continue }
+
+                if gesture !=  scrollView.panGestureRecognizer {
+                    return true
+                }
+            }
+        }
+
+        guard
+            state == .full,                   // When not .full, don't scroll.
+            interactionInProgress == false,   // When interaction already in progress, don't scroll.
+            scrollView.frame.contains(point), // When point not in scrollView, don't scroll.
+            !grabberAreaFrame.contains(point) // When point within grabber area, don't scroll.
+        else {
+            return false
+        }
+
+        log.debug("ScrollView.contentOffset >>>", scrollView.contentOffset.y)
+
+        let offset = scrollView.contentOffset.y - scrollView.contentOffsetZero.y
+        if  abs(offset) > offsetThreshold {
+            return true
+        }
+        if scrollView.isDecelerating {
+            return true
+        }
+        if velocity.y < 0 {
+            return true
+        }
+
+        return false
+    }
+
     private func panningBegan() {
         // A user interaction does not always start from Began state of the pan gesture
         // because it can be recognized in scrolling a content in a content view controller.
-        // So I do nothing here.
-        log.debug("panningBegan \(initialFrame)")
+        // So do nothing here.
+        log.debug("panningBegan")
     }
 
     private func panningChange(with translation: CGPoint) {
         log.debug("panningChange")
-        if interactionInProgress == false {
-            startInteraction(with: translation)
-        }
 
         let currentY = getCurrentY(from: initialFrame, with: translation)
 
@@ -275,36 +403,73 @@ class FloatingPanel: NSObject, UIGestureRecognizerDelegate, UIScrollViewDelegate
             initialFrame = surfaceView.frame
         }
 
-        stopScrollDeceleration = (surfaceView.frame.minY > layoutAdapter.topY) // Projecting the dragging to the scroll dragging
+        stopScrollDeceleration = (surfaceView.frame.minY > layoutAdapter.topY) // Projecting the dragging to the scroll dragging or not
 
         let targetPosition = self.targetPosition(with: translation, velocity: velocity)
         let distance = self.distance(to: targetPosition, with: translation)
 
         endInteraction(for: targetPosition)
 
+        if isRemovalInteractionEnabled, isBottomState {
+            if startRemovalAnimation(with: translation, velocity: velocity, distance: distance) {
+                return
+            }
+        }
+
         viewcontroller.delegate?.floatingPanelDidEndDragging(viewcontroller, withVelocity: velocity, targetPosition: targetPosition)
         viewcontroller.delegate?.floatingPanelWillBeginDecelerating(viewcontroller)
 
         startAnimation(to: targetPosition, at: distance, with: velocity)
     }
 
+    private func startRemovalAnimation(with translation: CGPoint, velocity: CGPoint, distance: CGFloat) -> Bool {
+        let posY = layoutAdapter.positionY(for: state)
+        let currentY = getCurrentY(from: initialFrame, with: translation)
+        let safeAreaBottomY = layoutAdapter.safeAreaBottomY
+        let vth = behavior.removalVelocity
+        let pth = max(min(behavior.removalProgress, 1.0), 0.0)
+        let velocityVector = (distance != 0) ? CGVector(dx: 0, dy: max(min(velocity.y/distance, vth), 0.0)) : .zero
+
+        guard (safeAreaBottomY - posY) != 0 else { return false }
+        guard (currentY - posY) / (safeAreaBottomY - posY) >= pth || velocityVector.dy == vth else { return false }
+
+        viewcontroller.delegate?.floatingPanelDidEndDraggingToRemove(viewcontroller, withVelocity: velocity)
+        let animator = self.behavior.removalInteractionAnimator(self.viewcontroller, with: velocityVector)
+        animator.addAnimations { [weak self] in
+            guard let self = self else { return }
+            self.updateLayout(to: nil)
+        }
+        animator.addCompletion({ [weak self] (_) in
+            guard let self = self else { return }
+            self.viewcontroller.removePanelFromParent(animated: false)
+            self.viewcontroller.delegate?.floatingPanelDidEndRemove(self.viewcontroller)
+        })
+        animator.startAnimation()
+        return true
+    }
+
     private func startInteraction(with translation: CGPoint) {
+        /* Don't lock a scroll view to show a scroll indicator after hitting the top */
         log.debug("startInteraction")
         initialFrame = surfaceView.frame
+        if let scrollView = scrollView {
+            initialScrollOffset = scrollView.contentOffset
+        }
         transOffsetY = translation.y
-        viewcontroller.delegate?.floatingPanelWillBeginDragging(viewcontroller)
 
-        lockScrollView()
+        viewcontroller.delegate?.floatingPanelWillBeginDragging(viewcontroller)
 
         interactionInProgress = true
     }
 
     private func endInteraction(for targetPosition: FloatingPanelPosition) {
         log.debug("endInteraction for \(targetPosition)")
-        if targetPosition != .full {
-            lockScrollView(withBounce: true)
-        }
         interactionInProgress = false
+
+        // Prevent to keep a scoll view indicator visible at the half/tip position
+        if targetPosition != .full {
+            lockScrollView()
+        }
     }
 
     private func getCurrentY(from rect: CGRect, with translation: CGPoint) -> CGFloat {
@@ -329,12 +494,11 @@ class FloatingPanel: NSObject, UIGestureRecognizerDelegate, UIScrollViewDelegate
         let targetY = layoutAdapter.positionY(for: targetPosition)
         let velocityVector = (distance != 0) ? CGVector(dx: 0, dy: max(min(velocity.y/distance, 30.0), -30.0)) : .zero
         let animator = behavior.interactionAnimator(self.viewcontroller, to: targetPosition, with: velocityVector)
-        animator.isInterruptible = false // To prevent a backdrop color's punk
         animator.addAnimations { [weak self] in
             guard let self = self else { return }
             if self.state == targetPosition {
                 self.surfaceView.frame.origin.y = targetY
-                self.setBackdropAlpha(of: targetPosition)
+                self.layoutAdapter.setBackdropAlpha(of: targetPosition)
             } else {
                 self.updateLayout(to: targetPosition)
             }
@@ -358,8 +522,11 @@ class FloatingPanel: NSObject, UIGestureRecognizerDelegate, UIScrollViewDelegate
         self.animator = nil
         self.viewcontroller.delegate?.floatingPanelDidEndDecelerating(self.viewcontroller)
 
+        stopScrollDeceleration = false
         // Don't unlock scroll view in animating view when presentation layer != model layer
-        unlockScrollView()
+        if targetPosition == .full {
+            unlockScrollView()
+        }
     }
 
     private func distance(to targetPosition: FloatingPanelPosition, with translation: CGPoint) -> CGFloat {
@@ -377,6 +544,66 @@ class FloatingPanel: NSObject, UIGestureRecognizerDelegate, UIScrollViewDelegate
         }
     }
 
+    private func directionalPosition(with translation: CGPoint) -> FloatingPanelPosition {
+        let currentY = getCurrentY(from: initialFrame, with: translation)
+
+        let supportedPositions: Set = layoutAdapter.layout.supportedPositions
+
+        if supportedPositions.count == 1 {
+            return state
+        }
+
+        switch supportedPositions {
+        case [.full, .half]: return translation.y >= 0 ? .half : .full
+        case [.half, .tip]: return translation.y >= 0 ? .tip : .half
+        case [.full, .tip]: return translation.y >= 0 ? .tip : .full
+        default:
+            let middleY = layoutAdapter.middleY
+
+            switch state {
+            case .full:
+                if translation.y <= 0 {
+                    return .full
+                }
+                return currentY > middleY ? .tip : .half
+            case .half:
+                return translation.y >= 0 ? .tip : .full
+            case .tip:
+                if translation.y >= 0 {
+                    return .tip
+                }
+                return currentY > middleY ? .half : .full
+            }
+        }
+    }
+
+    private func redirectionalPosition(with translation: CGPoint) -> FloatingPanelPosition {
+        let currentY = getCurrentY(from: initialFrame, with: translation)
+
+        let supportedPositions: Set = layoutAdapter.layout.supportedPositions
+
+        if supportedPositions.count == 1 {
+            return state
+        }
+
+        switch supportedPositions {
+        case [.full, .half]: return translation.y >= 0 ? .full : .half
+        case [.half, .tip]: return translation.y >= 0 ? .half : .tip
+        case [.full, .tip]: return translation.y >= 0 ? .full : .tip
+        default:
+            let middleY = layoutAdapter.middleY
+
+            switch state {
+            case .full:
+                return currentY > middleY ? .half : .full
+            case .half:
+                return .half
+            case .tip:
+                return currentY > middleY ? .tip : .half
+            }
+        }
+    }
+
     // Distance travelled after decelerating to zero velocity at a constant rate.
     // Refer to the slides p176 of [Designing Fluid Interfaces](https://developer.apple.com/videos/play/wwdc2018/803/)
     private func project(initialVelocity: CGFloat) -> CGFloat {
@@ -388,7 +615,9 @@ class FloatingPanel: NSObject, UIGestureRecognizerDelegate, UIScrollViewDelegate
         let currentY = getCurrentY(from: initialFrame, with: translation)
         let supportedPositions: Set = layoutAdapter.layout.supportedPositions
 
-        assert(supportedPositions.count > 1)
+        if supportedPositions.count == 1 {
+            return state
+        }
 
         switch supportedPositions {
         case [.full, .half]:
@@ -399,14 +628,44 @@ class FloatingPanel: NSObject, UIGestureRecognizerDelegate, UIScrollViewDelegate
             return targetPosition(from: [.full, .tip], at: currentY, velocity: velocity)
         default:
             /*
-             [topY|full]---[th1]---[middleY|default]---[th2]---[bottomY|collapsed]
+             [topY|full]---[th1]---[middleY|half]---[th2]---[bottomY|tip]
              */
             let topY = layoutAdapter.topY
             let middleY = layoutAdapter.middleY
             let bottomY = layoutAdapter.bottomY
 
-            let th1 = (topY + middleY) / 2
-            let th2 = (middleY + bottomY) / 2
+            let target: FloatingPanelPosition
+            let forwardYDirection: Bool
+
+            switch state {
+            case .full:
+                target = .half
+                forwardYDirection = true
+            case .half:
+                if (currentY < middleY) {
+                    target = .full
+                    forwardYDirection = false
+                } else {
+                    target = .tip
+                    forwardYDirection = true
+                }
+            case .tip:
+                target = .half
+                forwardYDirection = false
+            }
+
+            let redirectionalProgress = max(min(behavior.redirectionalProgress(viewcontroller, from: state, to: target), 1.0), 0.0)
+
+            let th1: CGFloat
+            let th2: CGFloat
+
+            if forwardYDirection {
+                th1 = topY + (middleY - topY) * redirectionalProgress
+                th2 = middleY + (bottomY - middleY) * redirectionalProgress
+            } else {
+                th1 = middleY - (middleY - topY) * redirectionalProgress
+                th2 = bottomY - (bottomY - middleY) * redirectionalProgress
+            }
 
             switch currentY {
             case ..<th1:
@@ -446,7 +705,10 @@ class FloatingPanel: NSObject, UIGestureRecognizerDelegate, UIScrollViewDelegate
         let topY = layoutAdapter.positionY(for: top)
         let bottomY = layoutAdapter.positionY(for: bottom)
 
-        let th = (topY + bottomY) / 2
+        let target = top == state ? bottom : top
+        let redirectionalProgress = max(min(behavior.redirectionalProgress(viewcontroller, from: state, to: target), 1.0), 0.0)
+
+        let th = topY + (bottomY - topY) * redirectionalProgress
 
         switch currentY {
         case ..<th:
@@ -466,17 +728,15 @@ class FloatingPanel: NSObject, UIGestureRecognizerDelegate, UIScrollViewDelegate
 
     // MARK: - ScrollView handling
 
-    func lockScrollView(withBounce bounce: Bool = false) {
+    private func lockScrollView() {
         guard let scrollView = scrollView else { return }
 
         scrollView.isDirectionalLockEnabled = true
-        if bounce {
-            scrollView.bounces = false
-        }
+        scrollView.bounces = false
         scrollView.showsVerticalScrollIndicator = false
     }
 
-    func unlockScrollView() {
+    private func unlockScrollView() {
         guard let scrollView = scrollView else { return }
 
         scrollView.isDirectionalLockEnabled = false
@@ -498,6 +758,13 @@ class FloatingPanel: NSObject, UIGestureRecognizerDelegate, UIScrollViewDelegate
         }
     }
 
+    func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
+        if state != .full {
+            initialScrollOffset = scrollView.contentOffset
+        }
+        userScrollViewDelegate?.scrollViewDidEndScrollingAnimation?(scrollView)
+    }
+
     func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
         if stopScrollDeceleration {
             targetContentOffset.pointee = scrollView.contentOffset

Framework/Sources/FloatingPanelBehavior.swift

@@ -6,7 +6,12 @@
 import UIKit
 
 public protocol FloatingPanelBehavior {
-    /// Returns a UIViewPropertyAnimator object for interacting with a floating panel by a user pan gesture
+    /// Returns the progress to redirect to the previous position
+    ///
+    /// The progress is represented by a floating-point value between 0.0 and 1.0, inclusive, where 1.0 indicates the floating panel is impossible to move to the next posiiton. The default value is 0.5. Values less than 0.0 and greater than 1.0 are pinned to those limits.
+    func redirectionalProgress(_ fpc: FloatingPanelController, from: FloatingPanelPosition, to: FloatingPanelPosition) -> CGFloat
+
+    /// Returns a UIViewPropertyAnimator object to project a floating panel to a position on finger up if the user dragged.
     func interactionAnimator(_ fpc: FloatingPanelController, to targetPosition: FloatingPanelPosition, with velocity: CGVector) -> UIViewPropertyAnimator
 
     /// Returns a UIViewPropertyAnimator object to add a floating panel to a position.
@@ -26,9 +31,28 @@ public protocol FloatingPanelBehavior {
     /// Its animator instance will be used to animate the surface view in `FloatingPanelController.move(to:animated:completion:)`.
     /// Default is an animator with ease-in-out curve and 0.25 sec duration.
     func moveAnimator(_ fpc: FloatingPanelController, from: FloatingPanelPosition, to: FloatingPanelPosition) -> UIViewPropertyAnimator
+
+    /// Returns a y-axis velocity to invoke a removal interaction at the bottom position.
+    ///
+    /// Default is 10.0. This method is called when FloatingPanelController.isRemovalInteractionEnabled is true.
+    var removalVelocity: CGFloat { get }
+
+    /// Returns the threshold of the transition to invoke a removal interaction at the bottom position.
+    ///
+    /// The progress is represented by a floating-point value between 0.0 and 1.0, inclusive, where 1.0 indicates the floating panel is impossible to invoke the removal interaction. The default value is 0.5. Values less than 0.0 and greater than 1.0 are pinned to those limits. This method is called when FloatingPanelController.isRemovalInteractionEnabled is true.
+    var removalProgress: CGFloat { get }
+
+    /// Returns a UIViewPropertyAnimator object to remove a floating panel with a velocity interactively at the bottom position.
+    ///
+    /// Default is a spring animator with 1.0 damping ratio. This method is called when FloatingPanelController.isRemovalInteractionEnabled is true.
+    func removalInteractionAnimator(_ fpc: FloatingPanelController, with velocity: CGVector) -> UIViewPropertyAnimator
 }
 
 public extension FloatingPanelBehavior {
+    func redirectionalProgress(_ fpc: FloatingPanelController, from: FloatingPanelPosition, to: FloatingPanelPosition) -> CGFloat {
+        return 0.5
+    }
+
     func addAnimator(_ fpc: FloatingPanelController, to: FloatingPanelPosition) -> UIViewPropertyAnimator {
         return UIViewPropertyAnimator(duration: 0.25, curve: .easeInOut)
     }
@@ -40,15 +64,31 @@ public extension FloatingPanelBehavior {
     func moveAnimator(_ fpc: FloatingPanelController, from: FloatingPanelPosition, to: FloatingPanelPosition) -> UIViewPropertyAnimator {
         return UIViewPropertyAnimator(duration: 0.25, curve: .easeInOut)
     }
+
+    var removalVelocity: CGFloat {
+        return 10.0
+    }
+
+    var removalProgress: CGFloat {
+        return 0.5
+    }
+
+    func removalInteractionAnimator(_ fpc: FloatingPanelController, with velocity: CGVector) -> UIViewPropertyAnimator {
+        log.debug("velocity", velocity)
+        let timing = UISpringTimingParameters(dampingRatio: 1.0,
+                                        frequencyResponse: 0.3,
+                                        initialVelocity: velocity)
+        return UIViewPropertyAnimator(duration: 0, timingParameters: timing)
+    }
 }
 
 class FloatingPanelDefaultBehavior: FloatingPanelBehavior {
     func interactionAnimator(_ fpc: FloatingPanelController, to targetPosition: FloatingPanelPosition, with velocity: CGVector) -> UIViewPropertyAnimator {
-        let timing = timeingCurve(to: targetPosition, with: velocity)
+        let timing = timeingCurve(with: velocity)
         return UIViewPropertyAnimator(duration: 0, timingParameters: timing)
     }
 
-    private func timeingCurve(to: FloatingPanelPosition, with velocity: CGVector) -> UITimingCurveProvider {
+    private func timeingCurve(with velocity: CGVector) -> UITimingCurveProvider {
         log.debug("velocity", velocity)
         let damping = self.getDamping(with: velocity)
         return UISpringTimingParameters(dampingRatio: damping,

Framework/Sources/FloatingPanelController.swift

@@ -12,6 +12,8 @@ public protocol FloatingPanelControllerDelegate: class {
     // if it returns nil, FloatingPanelController uses the default behavior
     func floatingPanel(_ vc: FloatingPanelController, behaviorFor newCollection: UITraitCollection) -> FloatingPanelBehavior?
 
+    func floatingPanelDidChangePosition(_ vc: FloatingPanelController) // changed the settled position in the model layer
+
     func floatingPanelDidMove(_ vc: FloatingPanelController) // any offset changes
 
     // called on start of dragging (may require some time and or distance to move)
@@ -20,6 +22,11 @@ public protocol FloatingPanelControllerDelegate: class {
     func floatingPanelDidEndDragging(_ vc: FloatingPanelController, withVelocity velocity: CGPoint, targetPosition: FloatingPanelPosition)
     func floatingPanelWillBeginDecelerating(_ vc: FloatingPanelController) // called on finger up as we are moving
     func floatingPanelDidEndDecelerating(_ vc: FloatingPanelController) // called when scroll view grinds to a halt
+
+    // called on start of dragging to remove its views from a parent view controller
+    func floatingPanelDidEndDraggingToRemove(_ vc: FloatingPanelController, withVelocity velocity: CGPoint)
+    // called when its views are removed from a parent view controller
+    func floatingPanelDidEndRemove(_ vc: FloatingPanelController)
 }
 
 public extension FloatingPanelControllerDelegate {
@@ -29,11 +36,15 @@ public extension FloatingPanelControllerDelegate {
     func floatingPanel(_ vc: FloatingPanelController, behaviorFor newCollection: UITraitCollection) -> FloatingPanelBehavior? {
         return nil
     }
+    func floatingPanelDidChangePosition(_ vc: FloatingPanelController) {}
     func floatingPanelDidMove(_ vc: FloatingPanelController) {}
     func floatingPanelWillBeginDragging(_ vc: FloatingPanelController) {}
     func floatingPanelDidEndDragging(_ vc: FloatingPanelController, withVelocity velocity: CGPoint, targetPosition: FloatingPanelPosition) {}
     func floatingPanelWillBeginDecelerating(_ vc: FloatingPanelController) {}
     func floatingPanelDidEndDecelerating(_ vc: FloatingPanelController) {}
+
+    func floatingPanelDidEndDraggingToRemove(_ vc: FloatingPanelController, withVelocity velocity: CGPoint) {}
+    func floatingPanelDidEndRemove(_ vc: FloatingPanelController) {}
 }
 
 public enum FloatingPanelPosition: Int, CaseIterable {
@@ -81,6 +92,16 @@ public class FloatingPanelController: UIViewController, UIScrollViewDelegate, UI
         return floatingPanel.state
     }
 
+    /// The layout object managed by the controller
+    public var layout: FloatingPanelLayout {
+        return floatingPanel.layoutAdapter.layout
+    }
+
+    /// The behavior object managed by the controller
+    public var behavior: FloatingPanelBehavior {
+        return floatingPanel.behavior
+    }
+
     /// The content insets of the tracking scroll view derived from the safe area of the parent view
     public var adjustedContentInsets: UIEdgeInsets {
         return floatingPanel.layoutAdapter.adjustedContentInsets
@@ -91,7 +112,21 @@ public class FloatingPanelController: UIViewController, UIScrollViewDelegate, UI
     /// This property specifies how the content area of the tracking scroll view is modified using `adjustedContentInsets`. The default value of this property is FloatingPanelController.ContentInsetAdjustmentBehavior.always.
     public var contentInsetAdjustmentBehavior: ContentInsetAdjustmentBehavior = .always
 
+    /// A Boolean value that determines whether the removal interaction is enabled.
+    public var isRemovalInteractionEnabled: Bool {
+        set { floatingPanel.isRemovalInteractionEnabled = newValue }
+        get { return floatingPanel.isRemovalInteractionEnabled }
+    }
+
+    /// The view controller responsible for the content portion of the floating panel.
+    public var contentViewController: UIViewController? {
+        set { set(contentViewController: newValue) }
+        get { return _contentViewController }
+    }
+    private var _contentViewController: UIViewController?
+
     private var floatingPanel: FloatingPanel!
+    private var layoutInsetsObservations: [NSKeyValueObservation] = []
 
     required init?(coder aDecoder: NSCoder) {
         super.init(coder: aDecoder)
@@ -124,13 +159,9 @@ public class FloatingPanelController: UIViewController, UIScrollViewDelegate, UI
         super.willTransition(to: newCollection, with: coordinator)
 
         // Change layout for a new trait collection
-        floatingPanel.layoutAdapter.layout = fetchLayout(for: newCollection)
+        updateLayout(for: newCollection)
+
         floatingPanel.behavior = fetchBehavior(for: newCollection)
-
-        guard let parent = parent else { fatalError() }
-
-        floatingPanel.layoutAdapter.prepareLayout(toParent: parent)
-        floatingPanel.layoutAdapter.activateLayout(of: floatingPanel.state)
     }
 
     public override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
@@ -140,7 +171,6 @@ public class FloatingPanelController: UIViewController, UIScrollViewDelegate, UI
         if let parent = parent {
             self.update(safeAreaInsets: parent.layoutInsets)
         }
-        floatingPanel.backdropView.isHidden = (traitCollection.verticalSizeClass == .compact)
     }
 
     public override func viewDidAppear(_ animated: Bool) {
@@ -168,7 +198,13 @@ public class FloatingPanelController: UIViewController, UIScrollViewDelegate, UI
     }
 
     private func update(safeAreaInsets: UIEdgeInsets) {
+        // preserve the current content offset
+        let contentOffset = scrollView?.contentOffset
+
         floatingPanel.safeAreaInsets = safeAreaInsets
+
+        scrollView?.contentOffset = contentOffset ?? .zero
+
         switch contentInsetAdjustmentBehavior {
         case .always:
             scrollView?.contentInset = adjustedContentInsets
@@ -178,6 +214,15 @@ public class FloatingPanelController: UIViewController, UIScrollViewDelegate, UI
         }
     }
 
+    private func updateLayout(for traitCollection: UITraitCollection) {
+        floatingPanel.layoutAdapter.layout = fetchLayout(for: traitCollection)
+
+        guard let parent = parent else { return }
+
+        floatingPanel.layoutAdapter.prepareLayout(toParent: parent)
+        floatingPanel.layoutAdapter.activateLayout(of: floatingPanel.state)
+    }
+
     // MARK: - Container view controller interface
 
     /// Adds the view managed by the controller as a child of the specified view controller.
@@ -191,8 +236,10 @@ public class FloatingPanelController: UIViewController, UIScrollViewDelegate, UI
             return
         }
         precondition((parent is UINavigationController) == false, "UINavigationController displays only one child view controller at a time.")
-        precondition((parent is UITableViewController) == false, "UITableViewController should not be the parent because the view hierarchy will be break in reusing cells.")
-        precondition((parent is UICollectionViewController) == false, "UICollectionViewController should not be the parent because the view hierarchy will be break in reusing cells.")
+        precondition((parent is UITabBarController) == false, "UITabBarController displays child view controllers with a radio-style selection interface")
+        precondition((parent is UISplitViewController) == false, "UISplitViewController manages two child view controllers in a master-detail interface")
+        precondition((parent is UITableViewController) == false, "UITableViewController should not be the parent because the view is a table view so that a floating panel doens't work well")
+        precondition((parent is UICollectionViewController) == false, "UICollectionViewController should not be the parent because the view is a collection view so that a floating panel doens't work well")
 
         view.frame = parent.view.bounds
         if let belowView = belowView {
@@ -201,11 +248,33 @@ public class FloatingPanelController: UIViewController, UIScrollViewDelegate, UI
             parent.view.addSubview(self.view)
         }
 
+        layoutInsetsObservations.removeAll()
+
+        // Must track safeAreaInsets/{top,bottom}LayoutGuide of the `parent.view`
+        // to update floatingPanel.safeAreaInsets`. There are 2 reasons.
+        // 1. The parent VC doesn't call viewSafeAreaInsetsDidChange() on the bottom
+        // inset's update expectedly.
+        // 2. The safe area top inset can be variable on the large title navigation bar.
+        // That's why it needs the observation to keep `adjustedContentInsets` correct.
+        if #available(iOS 11.0, *) {
+            let observaion = parent.observe(\.view.safeAreaInsets) { [weak self] (vc, chaneg) in
+                guard let self = self else { return }
+                self.update(safeAreaInsets: vc.layoutInsets)
+            }
+            layoutInsetsObservations.append(observaion)
+        } else {
+            // KVOs for topLayoutGuide & bottomLayoutGuide are not effective.
+            // Instead, safeAreaInsets will be updated in viewDidAppear()
+        }
+
         parent.addChild(self)
 
         // Must set a layout again here because `self.traitCollection` is applied correctly once it's added to a parent VC
         floatingPanel.layoutAdapter.layout = fetchLayout(for: traitCollection)
-        floatingPanel.layoutViews(in: parent)
+        floatingPanel.behavior = fetchBehavior(for: traitCollection)
+
+        floatingPanel.setUpViews(in: parent)
+
         floatingPanel.present(animated: animated) { [weak self] in
             guard let self = self else { return }
             self.didMove(toParent: parent)
@@ -222,11 +291,14 @@ public class FloatingPanelController: UIViewController, UIScrollViewDelegate, UI
             return
         }
 
+        layoutInsetsObservations.removeAll()
+
         floatingPanel.dismiss(animated: animated) { [weak self] in
             guard let self = self else { return }
 
             self.willMove(toParent: nil)
             self.view.removeFromSuperview()
+	      	self.backdropView.removeFromSuperview()
             self.removeFromParent()
             completion?()
         }
@@ -241,20 +313,36 @@ public class FloatingPanelController: UIViewController, UIScrollViewDelegate, UI
         floatingPanel.move(to: to, animated: animated, completion: completion)
     }
 
-    /// Presents the specified view controller as the content view controller in the surface view interface.
+    /// Sets the view controller responsible for the content portion of the floating panel..
+    public func set(contentViewController: UIViewController?) {
+        if let vc = _contentViewController {
+            vc.willMove(toParent: nil)
+            vc.view.removeFromSuperview()
+            vc.removeFromParent()
+        }
+
+        if let vc = contentViewController {
+            let surfaceView = self.view as! FloatingPanelSurfaceView
+            surfaceView.add(childView: vc.view)
+            addChild(vc)
+            vc.didMove(toParent: self)
+        }
+
+        _contentViewController = contentViewController
+    }
+
+    @available(*, unavailable, renamed: "set(contentViewController:)")
     public override func show(_ vc: UIViewController, sender: Any?) {
-        let surfaceView = self.view as! FloatingPanelSurfaceView
-        surfaceView.contentView.addSubview(vc.view)
-        vc.view.frame = surfaceView.contentView.bounds
-        vc.view.translatesAutoresizingMaskIntoConstraints = false
-        NSLayoutConstraint.activate([
-            vc.view.topAnchor.constraint(equalTo: surfaceView.contentView.topAnchor, constant: 0.0),
-            vc.view.leftAnchor.constraint(equalTo: surfaceView.contentView.leftAnchor, constant: 0.0),
-            vc.view.rightAnchor.constraint(equalTo: surfaceView.contentView.rightAnchor, constant: 0.0),
-            vc.view.bottomAnchor.constraint(equalTo: surfaceView.contentView.bottomAnchor, constant: 0.0),
-            ])
-        addChild(vc)
-        vc.didMove(toParent: self)
+        if let target = self.parent?.targetViewController(forAction: #selector(UIViewController.show(_:sender:)), sender: sender) {
+            target.show(vc, sender: sender)
+        }
+    }
+
+    @available(*, unavailable, renamed: "set(contentViewController:)")
+    public override func showDetailViewController(_ vc: UIViewController, sender: Any?) {
+        if let target = self.parent?.targetViewController(forAction: #selector(UIViewController.showDetailViewController(_:sender:)), sender: sender) {
+            target.showDetailViewController(vc, sender: sender)
+        }
     }
 
     // MARK: - Scroll view tracking
@@ -266,8 +354,10 @@ public class FloatingPanelController: UIViewController, UIScrollViewDelegate, UI
     ///
     public func track(scrollView: UIScrollView) {
         floatingPanel.scrollView = scrollView
-        floatingPanel.userScrollViewDelegate = scrollView.delegate
-        scrollView.delegate = floatingPanel
+        if scrollView.delegate !== floatingPanel {
+            floatingPanel.userScrollViewDelegate = scrollView.delegate
+            scrollView.delegate = floatingPanel
+        }
         switch contentInsetAdjustmentBehavior {
         case .always:
             if #available(iOS 11.0, *) {
@@ -282,7 +372,18 @@ public class FloatingPanelController: UIViewController, UIScrollViewDelegate, UI
         }
     }
 
-    // MARK: - Helpers
+    // MARK: - Utilities
+
+    /// Updates the layout object from the delegate and lays out the views managed
+    /// by the controller immediately.
+    ///
+    /// This method updates the `FloatingPanelLayout` object from the delegate and
+    /// then it calls `layoutIfNeeded()` of the parent's root view to force the view
+    /// to update the floating panel's layout immediately. It can be called in an
+    /// animation block.
+    public func updateLayout() {
+        updateLayout(for: view.traitCollection)
+    }
 
     /// Returns the y-coordinate of the point at the origin of the surface view
     public func originYOfSurface(for pos: FloatingPanelPosition) -> CGFloat {

Framework/Sources/FloatingPanelLayout.swift

@@ -30,16 +30,17 @@ public protocol FloatingPanelLayout: class {
     /// By default, the width of a surface view fits a safe area.
     func prepareLayout(surfaceView: UIView, in view: UIView) -> [NSLayoutConstraint]
 
-    /// Return the backdrop alpha of black color in full position. Default is 0.3.
-    var backdropAlpha: CGFloat { get }
+    /// Returns a CGFloat value to determine the backdrop view's alpha for a position.
+    ///
+    /// Default is 0.3 at full position, otherwise 0.0.
+    func backdropAlphaFor(position: FloatingPanelPosition) -> CGFloat
 }
 
 public extension FloatingPanelLayout {
-    var backdropAlpha: CGFloat { return 0.3 }
     var topInteractionBuffer: CGFloat { return 6.0 }
     var bottomInteractionBuffer: CGFloat { return 6.0 }
 
-    public var supportedPositions: Set<FloatingPanelPosition> {
+    var supportedPositions: Set<FloatingPanelPosition> {
         return Set(FloatingPanelPosition.allCases)
     }
     
@@ -49,6 +50,10 @@ public extension FloatingPanelLayout {
             surfaceView.rightAnchor.constraint(equalTo: view.sideLayoutGuide.rightAnchor, constant: 0.0),
         ]
     }
+
+    func backdropAlphaFor(position: FloatingPanelPosition) -> CGFloat {
+        return position == .full ? 0.3 : 0.0
+    }
 }
 
 public class FloatingPanelDefaultLayout: FloatingPanelLayout {
@@ -80,37 +85,35 @@ public class FloatingPanelDefaultLandscapeLayout: FloatingPanelLayout {
         default: return nil
         }
     }
-
-    public func prepareLayout(surfaceView: UIView, in view: UIView) -> [NSLayoutConstraint] {
-        return [
-            surfaceView.leftAnchor.constraint(equalTo: view.sideLayoutGuide.leftAnchor, constant: 0.0),
-            surfaceView.rightAnchor.constraint(equalTo: view.sideLayoutGuide.rightAnchor, constant: 0.0),
-        ]
-    }
 }
 
 
 class FloatingPanelLayoutAdapter {
+    private weak var parent: UIViewController!
     private weak var surfaceView: FloatingPanelSurfaceView!
-    private weak var backdropVIew: FloatingPanelBackdropView!
+    private weak var backdropView: FloatingPanelBackdropView!
 
     var layout: FloatingPanelLayout {
-        didSet { checkConsistance(of: layout) }
+        didSet {
+            checkLayoutConsistance()
+        }
     }
 
     var safeAreaInsets: UIEdgeInsets = .zero {
         didSet {
             updateHeight()
+            checkLayoutConsistance()
         }
     }
 
+    private var parentHeight: CGFloat = 0.0
     private var heightBuffer: CGFloat = 88.0 // For bounce
     private var fixedConstraints: [NSLayoutConstraint] = []
     private var fullConstraints: [NSLayoutConstraint] = []
     private var halfConstraints: [NSLayoutConstraint] = []
     private var tipConstraints: [NSLayoutConstraint] = []
     private var offConstraints: [NSLayoutConstraint] = []
-    private var heightConstraints: NSLayoutConstraint? = nil
+    private var heightConstraints: [NSLayoutConstraint] = []
 
     private var fullInset: CGFloat {
         return layout.insetFor(position: .full) ?? 0.0
@@ -142,6 +145,10 @@ class FloatingPanelLayoutAdapter {
         }
     }
 
+    var safeAreaBottomY: CGFloat {
+        return surfaceView.superview!.bounds.height - (safeAreaInsets.bottom)
+    }
+
     var adjustedContentInsets: UIEdgeInsets {
         return UIEdgeInsets(top: 0.0,
                             left: 0.0,
@@ -163,28 +170,30 @@ class FloatingPanelLayoutAdapter {
     init(surfaceView: FloatingPanelSurfaceView, backdropView: FloatingPanelBackdropView, layout: FloatingPanelLayout) {
         self.layout = layout
         self.surfaceView = surfaceView
-        self.backdropVIew = backdropView
+        self.backdropView = backdropView
     }
 
     func prepareLayout(toParent parent: UIViewController) {
+        self.parent = parent
+
         surfaceView.translatesAutoresizingMaskIntoConstraints = false
-        backdropVIew.translatesAutoresizingMaskIntoConstraints = false
+        backdropView.translatesAutoresizingMaskIntoConstraints = false
 
         NSLayoutConstraint.deactivate(fixedConstraints + fullConstraints + halfConstraints + tipConstraints + offConstraints)
 
         // Fixed constraints of surface and backdrop views
         let surfaceConstraints = layout.prepareLayout(surfaceView: surfaceView, in: parent.view!)
-        let backdroptConstraints = [
-            backdropVIew.topAnchor.constraint(equalTo: parent.view.topAnchor,
+        let backdropConstraints = [
+            backdropView.topAnchor.constraint(equalTo: parent.view.topAnchor,
                                               constant: 0.0),
-            backdropVIew.leftAnchor.constraint(equalTo: parent.view.leftAnchor,
+            backdropView.leftAnchor.constraint(equalTo: parent.view.leftAnchor,
                                                constant: 0.0),
-            backdropVIew.rightAnchor.constraint(equalTo: parent.view.rightAnchor,
+            backdropView.rightAnchor.constraint(equalTo: parent.view.rightAnchor,
                                                 constant: 0.0),
-            backdropVIew.bottomAnchor.constraint(equalTo: parent.view.bottomAnchor,
+            backdropView.bottomAnchor.constraint(equalTo: parent.view.bottomAnchor,
                                                  constant: 0.0),
             ]
-        fixedConstraints = surfaceConstraints + backdroptConstraints
+        fixedConstraints = surfaceConstraints + backdropConstraints
 
         // Flexible surface constarints for full, half, tip and off
         fullConstraints = [
@@ -200,7 +209,7 @@ class FloatingPanelLayoutAdapter {
                                              constant: -tipInset),
         ]
         offConstraints = [
-            surfaceView.topAnchor.constraint(equalTo: parent.layoutGuide.bottomAnchor, constant: 0.0),
+            surfaceView.topAnchor.constraint(equalTo: parent.view.bottomAnchor, constant: 0.0),
         ]
     }
 
@@ -213,22 +222,24 @@ class FloatingPanelLayoutAdapter {
             }
         }
 
-        if let consts = self.heightConstraints {
-            NSLayoutConstraint.deactivate([consts])
-        }
-
-        let height = UIScreen.main.bounds.height - (safeAreaInsets.top + fullInset)
-        let consts = surfaceView.heightAnchor.constraint(equalToConstant: height)
-
-        NSLayoutConstraint.activate([consts])
-        heightConstraints = consts
-        surfaceView.bottomOverflow = heightBuffer
+        NSLayoutConstraint.deactivate(heightConstraints)
+        // Must use the parent height, not the screen height because safe area insets
+        // of the parent are relative values. For example, a view controller in
+        // Navigation controller's safe area insets and frame can be changed whether
+        // the navigation bar is translucent or not.
+        let height = self.parent.view.bounds.height - (safeAreaInsets.top + fullInset)
+        heightConstraints = [
+            surfaceView.heightAnchor.constraint(equalToConstant: height)
+        ]
+        NSLayoutConstraint.activate(heightConstraints)
+        surfaceView.set(bottomOverflow: heightBuffer)
     }
 
     func activateLayout(of state: FloatingPanelPosition?) {
         defer {
             surfaceView.superview!.layoutIfNeeded()
         }
+        setBackdropAlpha(of: state)
 
         NSLayoutConstraint.activate(fixedConstraints)
 
@@ -256,15 +267,27 @@ class FloatingPanelLayoutAdapter {
         }
     }
 
-    private func checkConsistance(of layout: FloatingPanelLayout) {
+    func setBackdropAlpha(of target: FloatingPanelPosition?) {
+        if let target = target {
+            self.backdropView.alpha = layout.backdropAlphaFor(position: target)
+        } else {
+            self.backdropView.alpha = 0.0
+        }
+    }
+
+    func checkLayoutConsistance() {
         // Verify layout configurations
-        assert(layout.supportedPositions.count > 1)
-        assert(layout.supportedPositions.contains(layout.initialPosition),
-               "Does not include an initial potision(\(layout.initialPosition)) in supportedPositions(\(layout.supportedPositions))")
-        layout.supportedPositions.forEach { (pos) in
+        let supportedPositions = layout.supportedPositions
+
+        assert(supportedPositions.count > 0)
+        assert(supportedPositions.contains(layout.initialPosition),
+               "Does not include an initial potision(\(layout.initialPosition)) in supportedPositions(\(supportedPositions))")
+
+        supportedPositions.forEach { pos in
             assert(layout.insetFor(position: pos) != nil,
                    "Undefined an inset for a pos(\(pos))")
         }
+
         if halfInset > 0 {
             assert(halfInset > tipInset, "Invalid half and tip insets")
         }

Framework/Sources/FloatingPanelSurfaceView.swift

@@ -21,15 +21,12 @@ public class FloatingPanelSurfaceView: UIView {
     /// A UIView object that can have the surface view added to it.
     public var contentView: UIView!
 
-    private var color: UIColor? = .white { didSet { setNeedsDisplay() } }
-    var bottomOverflow: CGFloat = 0.0 { didSet { setNeedsDisplay() }}
+    private var color: UIColor? = .white { didSet { setNeedsLayout() } }
+    private var bottomOverflow: CGFloat = 0.0 // Must not call setNeedsLayout()
 
     public override var backgroundColor: UIColor? {
         get { return color }
-        set {
-            color = newValue
-            setNeedsDisplay()
-        }
+        set { color = newValue }
     }
 
     /// The radius to use when drawing top rounded corners.
@@ -59,7 +56,7 @@ public class FloatingPanelSurfaceView: UIView {
     /// The color of the surface border.
     public var borderWidth: CGFloat = 0.0  { didSet { setNeedsLayout() } }
 
-    private var shadowLayer: CAShapeLayer!  { didSet { setNeedsLayout() } }
+    private var backgroundLayer: CAShapeLayer!  { didSet { setNeedsLayout() } }
 
     private struct Default {
         public static let grabberTopPadding: CGFloat = 6.0
@@ -79,10 +76,14 @@ public class FloatingPanelSurfaceView: UIView {
         super.backgroundColor = .clear
         self.clipsToBounds = false
 
+        let backgroundLayer = CAShapeLayer()
+        layer.insertSublayer(backgroundLayer, at: 0)
+        self.backgroundLayer = backgroundLayer
+
         let contentView = FloatingPanelSurfaceContentView()
         addSubview(contentView)
         self.contentView = contentView as UIView
-        // contentView.backgroundColor = .lightGray
+        contentView.backgroundColor = color
         contentView.translatesAutoresizingMaskIntoConstraints = false
         NSLayoutConstraint.activate([
             contentView.topAnchor.constraint(equalTo: topAnchor, constant: 0.0),
@@ -102,17 +103,39 @@ public class FloatingPanelSurfaceView: UIView {
             grabberHandle.heightAnchor.constraint(equalToConstant: grabberHandle.frame.height),
             grabberHandle.centerXAnchor.constraint(equalTo: centerXAnchor),
             ])
-
-        let shadowLayer = CAShapeLayer()
-        layer.insertSublayer(shadowLayer, at: 0)
-        self.shadowLayer = shadowLayer
     }
 
     public override func layoutSubviews() {
         super.layoutSubviews()
 
-        updateShadowLayer()
+        updateLayers()
+        updateContentViewMask()
 
+        contentView.layer.borderColor = borderColor?.cgColor
+        contentView.layer.borderWidth = borderWidth
+        contentView.backgroundColor = color
+    }
+
+    private func updateLayers() {
+        log.debug("SurfaceView bounds", bounds)
+        
+        var rect = bounds
+        rect.size.height += bottomOverflow // Expand the height for overflow buffer
+        let path = UIBezierPath(roundedRect: rect,
+                                byRoundingCorners: [.topLeft, .topRight],
+                                cornerRadii: CGSize(width: cornerRadius, height: cornerRadius))
+        backgroundLayer.path = path.cgPath
+        backgroundLayer.fillColor = color?.cgColor
+		
+        if shadowHidden == false {
+            layer.shadowColor = shadowColor.cgColor
+            layer.shadowOffset = shadowOffset
+            layer.shadowOpacity = shadowOpacity
+            layer.shadowRadius = shadowRadius
+        }
+    }
+
+    private func updateContentViewMask() {
         if #available(iOS 11, *) {
             // Don't use `contentView.clipToBounds` because it prevents content view from expanding the height of a subview of it
             // for the bottom overflow like Auto Layout settings of UIVisualEffectView in Main.storyborad of Example/Maps.
@@ -129,26 +152,24 @@ public class FloatingPanelSurfaceView: UIView {
             // Don't use `contentView.layer.mask` because of a UIVisualEffectView issue in iOS 10, https://forums.developer.apple.com/thread/50854
             // Instead, a user can mask the content view manually in an application.
         }
-
-        contentView.layer.borderColor = borderColor?.cgColor
-        contentView.layer.borderWidth = borderWidth
     }
 
-    private func updateShadowLayer() {
-        log.debug("SurfaceView bounds", bounds)
-        var rect = bounds
-        rect.size.height += bottomOverflow // Expand the height for overflow buffer
-        let path = UIBezierPath(roundedRect: rect,
-                                byRoundingCorners: [.topLeft, .topRight],
-                                cornerRadii: CGSize(width: cornerRadius, height: cornerRadius))
-        shadowLayer.path = path.cgPath
-        shadowLayer.fillColor = color?.cgColor
-        if shadowHidden == false {
-            shadowLayer.shadowPath = shadowLayer.path
-            shadowLayer.shadowColor = shadowColor.cgColor
-            shadowLayer.shadowOffset = shadowOffset
-            shadowLayer.shadowOpacity = shadowOpacity
-            shadowLayer.shadowRadius = shadowRadius
-        }
+    func set(bottomOverflow: CGFloat) {
+        self.bottomOverflow = bottomOverflow
+        updateLayers()
+        updateContentViewMask()
+    }
+
+
+    func add(childView: UIView) {
+        contentView.addSubview(childView)
+        childView.frame = contentView.bounds
+        childView.translatesAutoresizingMaskIntoConstraints = false
+        NSLayoutConstraint.activate([
+            childView.topAnchor.constraint(equalTo: contentView.topAnchor, constant: 0.0),
+            childView.leftAnchor.constraint(equalTo: contentView.leftAnchor, constant: 0.0),
+            childView.rightAnchor.constraint(equalTo: contentView.rightAnchor, constant: 0.0),
+            childView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: 0.0),
+            ])
     }
 }

Framework/Sources/GrabberHandleView.swift

@@ -24,8 +24,14 @@ public class GrabberHandleView: UIView {
         self.backgroundColor = Default.barColor
         render()
     }
+
     private func render() {
         self.layer.masksToBounds = true
         self.layer.cornerRadius = frame.size.height * 0.5
     }
+
+    public override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
+        let view = super.hitTest(point, with: event)
+        return view == self ? nil : view
+    }
 }

Framework/Sources/UIExtensions.swift

@@ -50,6 +50,8 @@ protocol SideLayoutGuideProvider {
 extension UIView: SideLayoutGuideProvider {}
 extension UILayoutGuide: SideLayoutGuideProvider {}
 
+// The reason why UIView has no extensions of safe area insets and top/bottom guides
+// is for iOS10 compat.
 extension UIView {
     var sideLayoutGuide: SideLayoutGuideProvider {
         if #available(iOS 11.0, *) {

README.md

@@ -24,15 +24,18 @@ The new interface displays the related contents and utilities in parallel as a u
   - [Carthage](#carthage)
 - [Getting Started](#getting-started)
 - [Usage](#usage)
-  - [Customize the layout of a floating panel with  `FloatingPanelLayout` protocol](#customize-the-layout-of-a-floating-panel-with--floatingpanellayout-protocol)
-    - [Change the initial position, supported positions and height](#change-the-initial-position-supported-positions-and-height)
+  - [Customize the layout with `FloatingPanelLayout` protocol](#customize-the-layout-with-floatingpanellayout-protocol)
+    - [Change the initial position and height](#change-the-initial-position-and-height)
     - [Support your landscape layout](#support-your-landscape-layout)
   - [Customize the behavior with `FloatingPanelBehavior` protocol](#customize-the-behavior-with-floatingpanelbehavior-protocol)
     - [Modify your floating panel's interaction](#modify-your-floating-panels-interaction)
+  - [Use a custom grabber handle](#use-a-custom-grabber-handle)
+  - [Add tap gestures to the surface or backdrop views](#add-tap-gestures-to-the-surface-or-backdrop-views)
   - [Create an additional floating panel for a detail](#create-an-additional-floating-panel-for-a-detail)
   - [Move a position with an animation](#move-a-position-with-an-animation)
-  - [Make your contents correspond with a floating panel behavior](#make-your-contents-correspond-with-a-floating-panel-behavior)
+  - [Work your contents together with a floating panel behavior](#work-your-contents-together-with-a-floating-panel-behavior)
 - [Notes](#notes)
+  - ['Show' or 'Show Detail' Segues from `FloatingPanelController`'s content view controller](#show-or-show-detail-segues-from-floatingpanelcontrollers-content-view-controller)
   - [FloatingPanelSurfaceView's issue on iOS 10](#floatingpanelsurfaceviews-issue-on-ios-10)
 - [Author](#author)
 - [License](#license)
@@ -45,7 +48,7 @@ The new interface displays the related contents and utilities in parallel as a u
 - [x] Fluid animation and gesture handling
 - [x] Scroll view tracking
 - [x] Common UI elements: Grabber handle, Backdrop and Surface rounding corners
-- [x] 2 or 3 anchor positions(full, half, tip)
+- [x] 1~3 anchor positions(full, half, tip)
 - [x] Layout customization for all trait environments(i.e. Landscape orientation support)
 - [x] Behavior customization
 - [x] Free from common issues of Auto Layout and gesture handling
@@ -96,14 +99,14 @@ class ViewController: UIViewController, FloatingPanelControllerDelegate {
         // Assign self as the delegate of the controller.
         fpc.delegate = self // Optional
 
-        // Add a content view controller.
+        // Set a content view controller.
         let contentVC = ContentViewController()
-        fpc.show(contentVC, sender: nil)
+        fpc.set(contentViewController: contentVC)
 
         // Track a scroll view(or the siblings) in the content view controller.
         fpc.track(scrollView: contentVC.tableView)
 
-        // Add the views managed by the `FloatingPanelController` object to self.view.
+        // Add and show the views managed by the `FloatingPanelController` object to self.view.
         fpc.addPanel(toParent: self)
     }
 
@@ -118,7 +121,7 @@ class ViewController: UIViewController, FloatingPanelControllerDelegate {
 
 ## Usage
 
-### Customize the layout of a floating panel with  `FloatingPanelLayout` protocol
+### Customize the layout with `FloatingPanelLayout` protocol
 
 #### Change the initial position and height
 
@@ -210,6 +213,45 @@ class FloatingPanelStocksBehavior: FloatingPanelBehavior {
 }
 ```
 
+### Use a custom grabber handle
+
+```swift
+class ViewController: UIViewController {
+    ...
+    override func viewDidLoad() {
+        ...
+        let myGrabberHandleView = MyGrabberHandleView()
+        fpc.surfaceView.grabberHandle.isHidden = true
+        fpc.surfaceView.addSubview(myGrabberHandleView)
+    }
+    ...
+}
+```
+
+### Add tap gestures to the surface or backdrop views
+
+```swift
+class ViewController: UIViewController, FloatingPanelControllerDelegate {
+    ...
+    override func viewDidLoad() {
+        ...
+        surfaceTapGesture = UITapGestureRecognizer(target: self, action: #selector(handleSurface(tapGesture:)))
+        fpc.surfaceView.addGestureRecognizer(surfaceTapGesture)
+
+        backdropTapGesture = UITapGestureRecognizer(target: self, action: #selector(handleBackdrop(tapGesture:)))
+        fpc.backdropView.addGestureRecognizer(backdropTapGesture)
+
+        surfaceTapGesture.isEnabled = (fpc.position == .tip)
+        ...
+    }
+    ...
+    // Enable `surfaceTapGesture` only at `tip` position
+    func floatingPanelDidChangePosition(_ vc: FloatingPanelController) {
+        surfaceTapGesture.isEnabled = (vc.position == .tip)
+    }
+}
+```
+
 ### Create an additional floating panel for a detail
 
 ```swift
@@ -222,7 +264,7 @@ class ViewController: UIViewController, FloatingPanelControllerDelegate {
         self.searchPanelVC = FloatingPanelController()
 
         let searchVC = SearchViewController()
-        self.searchPanelVC.show(searchVC, sender: nil)
+        self.searchPanelVC.set(contentViewController: searchVC)
         self.searchPanelVC.track(scrollView: contentVC.tableView)
 
         self.searchPanelVC.addPanel(toParent: self)
@@ -231,7 +273,7 @@ class ViewController: UIViewController, FloatingPanelControllerDelegate {
         self.detailPanelVC = FloatingPanelController()
 
         let contentVC = ContentViewController()
-        self.detailPanelVC.show(contentVC, sender: nil)
+        self.detailPanelVC.set(contentViewController: contentVC)
         self.detailPanelVC.track(scrollView: contentVC.scrollView)
 
         self.detailPanelVC.addPanel(toParent: self)
@@ -256,7 +298,7 @@ In the following example, I move a floating panel to full or half position while
     }
 ```
 
-### Make your contents correspond with a floating panel behavior
+### Work your contents together with a floating panel behavior
 
 ```swift
 class ViewController: UIViewController, FloatingPanelControllerDelegate {
@@ -279,7 +321,40 @@ class ViewController: UIViewController, FloatingPanelControllerDelegate {
 
 ## Notes
 
-###  FloatingPanelSurfaceView's issue on iOS 10
+### 'Show' or 'Show Detail' Segues from `FloatingPanelController`'s content view controller
+
+'Show' or 'Show Detail' segues from a content view controller will be managed by a view controller(hereinafter called 'master VC') adding a floating panel. Because a floating panel is just a subview of the master VC.
+
+`FloatingPanelController` has no way to manage a stack of view controllers like `UINavigationController`. If so, it would be so complicated and the interface will become `UINavigationController`. This component should not have the responsibility to manage the stack.
+
+By the way, a content view controller can present a view controller modally with `present(_:animated:completion:)` or 'Present Modally' segue.
+
+However, sometimes you want to show a destination view controller of 'Show' or 'Show Detail' segue with another floating panel. It's possible to override `show(_:sender)` of the master VC!
+
+Here is an example.
+
+```swift
+class ViewController: UIViewController {
+    var fpc: FloatingPanelController!
+    var secondFpc: FloatingPanelController!
+
+    ...
+    override func show(_ vc: UIViewController, sender: Any?) {
+        secondFpc = FloatingPanelController()
+
+        secondFpc.set(contentViewController: vc)
+
+        secondFpc.addPanel(toParent: self)
+    }
+    ...
+}
+```
+
+A `FloatingPanelController` object proxies an action for `show(_:sender)` to the master VC. That's why the master VC can handle a destination view controller of a 'Show' or 'Show Detail' segue and you can hook `show(_:sender)` to show a secondally floating panel set the destination view controller to the content.
+
+It's a great way to decouple between a floating panel and the content VC.
+
+### FloatingPanelSurfaceView's issue on iOS 10
 
 * On iOS 10,   `FloatingPanelSurfaceView.cornerRadius` isn't not automatically masked with the top rounded corners  because of UIVisualEffectView issue. See https://forums.developer.apple.com/thread/50854. 
 So you need to draw top rounding corners of your content.  Here is an example in Examples/Maps.