Merge pull request #228 from SCENEE/fix-unexpected-layout-update

Fix an unexpected layout update on iOS13

Framework/Sources/FloatingPanelController.swift

@@ -196,7 +196,7 @@ open class FloatingPanelController: UIViewController, UIScrollViewDelegate, UIGe
         self.view = view as UIView
     }
 
-    open  override func viewDidLayoutSubviews() {
+    open override func viewDidLayoutSubviews() {
         super.viewDidLayoutSubviews()
         if #available(iOS 11.0, *) {}
         else {
@@ -207,7 +207,7 @@ open class FloatingPanelController: UIViewController, UIScrollViewDelegate, UIGe
         }
     }
 
-    open  override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
+    open override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
         super.viewWillTransition(to: size, with: coordinator)
 
         if view.translatesAutoresizingMaskIntoConstraints {
@@ -216,14 +216,9 @@ open class FloatingPanelController: UIViewController, UIScrollViewDelegate, UIGe
         }
     }
 
-    open  override func willTransition(to newCollection: UITraitCollection, with coordinator: UIViewControllerTransitionCoordinator) {
+    open override func willTransition(to newCollection: UITraitCollection, with coordinator: UIViewControllerTransitionCoordinator) {
         super.willTransition(to: newCollection, with: coordinator)
-
-        // Change layout for a new trait collection
-        reloadLayout(for: newCollection)
-        setUpLayout()
-
-        floatingPanel.behavior = fetchBehavior(for: newCollection)
+        self.prepare(for: newCollection)
     }
 
     open override func viewWillDisappear(_ animated: Bool) {
@@ -231,6 +226,15 @@ open class FloatingPanelController: UIViewController, UIScrollViewDelegate, UIGe
         safeAreaInsetsObservation = nil
     }
 
+    // MARK:- Internals
+    func prepare(for newCollection: UITraitCollection) {
+        guard newCollection.shouldUpdateLayout(from: traitCollection) else { return }
+        // Change a layout & behavior for a new trait collection
+        reloadLayout(for: newCollection)
+        activateLayout()
+        floatingPanel.behavior = fetchBehavior(for: newCollection)
+    }
+
     // MARK:- Privates
 
     private func fetchLayout(for traitCollection: UITraitCollection) -> FloatingPanelLayout {
@@ -257,7 +261,7 @@ open class FloatingPanelController: UIViewController, UIScrollViewDelegate, UIGe
         // Prevent an infinite loop on iOS 10: setUpLayout() -> viewDidLayoutSubviews() -> setUpLayout()
         preSafeAreaInsets = safeAreaInsets
 
-        setUpLayout()
+        activateLayout()
 
         switch contentInsetAdjustmentBehavior {
         case .always:
@@ -282,7 +286,7 @@ open class FloatingPanelController: UIViewController, UIScrollViewDelegate, UIGe
         }
     }
 
-    private func setUpLayout() {
+    private func activateLayout() {
         // preserve the current content offset
         let contentOffset = scrollView?.contentOffset
 
@@ -298,7 +302,7 @@ open class FloatingPanelController: UIViewController, UIScrollViewDelegate, UIGe
     public func show(animated: Bool = false, completion: (() -> Void)? = nil) {
         // Must apply the current layout here
         reloadLayout(for: traitCollection)
-        setUpLayout()
+        activateLayout()
 
         if #available(iOS 11.0, *) {
             // Must track the safeAreaInsets of `self.view` to update the layout.
@@ -513,7 +517,7 @@ open class FloatingPanelController: UIViewController, UIScrollViewDelegate, UIGe
     /// animation block.
     public func updateLayout() {
         reloadLayout(for: traitCollection)
-        setUpLayout()
+        activateLayout()
     }
 
     /// Returns the y-coordinate of the point at the origin of the surface view.

Framework/Sources/UIExtensions.swift

@@ -124,3 +124,12 @@ extension CGPoint {
                        y: CGFloat.nan)
     }
 }
+
+extension UITraitCollection {
+    func shouldUpdateLayout(from previous: UITraitCollection) -> Bool {
+        return previous.horizontalSizeClass != horizontalSizeClass
+            || previous.verticalSizeClass != verticalSizeClass
+            || previous.preferredContentSizeCategory != preferredContentSizeCategory
+            || previous.layoutDirection != layoutDirection
+    }
+}

Framework/Tests/FloatingPanelControllerTests.swift

@@ -28,7 +28,6 @@ class FloatingPanelControllerTests: XCTestCase {
 
     func test_addPanel() {
         guard let rootVC = UIApplication.shared.keyWindow?.rootViewController else { fatalError() }
-
         let fpc = FloatingPanelController()
         fpc.addPanel(toParent: rootVC)
 
@@ -39,6 +38,24 @@ class FloatingPanelControllerTests: XCTestCase {
         waitRunLoop(secs: 1.0)
         XCTAssert(fpc.surfaceView.frame.minY == (fpc.view.bounds.height - fpc.layoutInsets.bottom) - fpc.layout.insetFor(position: .tip)!)
     }
+
+    @available(iOS 12.0, *)
+    func test_updateLayout_willTransition() {
+        class MyDelegate: FloatingPanelControllerDelegate {
+            func floatingPanel(_ vc: FloatingPanelController, layoutFor newCollection: UITraitCollection) -> FloatingPanelLayout? {
+                if newCollection.userInterfaceStyle == .dark {
+                    XCTFail()
+                }
+                return nil
+            }
+        }
+        let myDelegate = MyDelegate()
+        let fpc = FloatingPanelController(delegate: myDelegate)
+        let traitCollection = UITraitCollection(traitsFrom: [fpc.traitCollection,
+                                                             UITraitCollection(userInterfaceStyle: .dark)])
+        XCTAssertEqual(traitCollection.userInterfaceStyle, .dark)
+        fpc.prepare(for: traitCollection)
+    }
 }
 
 func waitRunLoop(secs: TimeInterval = 0) {