Initial commit

Sources/UIKit/CollectionViewDiffableDataSource.swift

@@ -0,0 +1,133 @@
+#if os(iOS) || os(tvOS)
+
+import UIKit
+import DifferenceKit
+
+/// A class for backporting `UICollectionViewDiffableDataSource` introduced in iOS 13.0+, tvOS 13.0+.
+/// Represents the data model object for `UICollectionView` that can be applies the
+/// changes with automatic diffing.
+open class CollectionViewDiffableDataSource<SectionIdentifierType: Hashable, ItemIdentifierType: Hashable>: NSObject, UICollectionViewDataSource {
+    /// The type of closure providing the cell.
+    public typealias CellProvider = (UICollectionView, IndexPath, ItemIdentifierType) -> UICollectionViewCell?
+
+    /// The type of closure providing the supplementary view for element of kind.
+    public typealias SupplementaryViewProvider = (UICollectionView, String, IndexPath) -> UICollectionReusableView?
+
+    /// A closure to dequeue the views for element of kind.
+    public var supplementaryViewProvider: SupplementaryViewProvider?
+
+    private weak var collectionView: UICollectionView?
+    private let cellProvider: CellProvider
+    private let core = DiffableDataSourceCore<SectionIdentifierType, ItemIdentifierType>()
+
+    /// Creates a new data source.
+    ///
+    /// - Parameters:
+    ///   - collectionView: A collection view instance to be managed.
+    ///   - cellProvider: A closure to dequeue the cell for items.
+    public init(collectionView: UICollectionView, cellProvider: @escaping CellProvider) {
+        self.collectionView = collectionView
+        self.cellProvider = cellProvider
+        super.init()
+
+        collectionView.dataSource = self
+    }
+
+    /// Applies given snapshot to perform automatic diffing update.
+    ///
+    /// - Parameters:
+    ///   - snapshot: A snapshot object to be applied to data model.
+    ///   - animatingDifferences: A Boolean value indicating whether to update with
+    ///                           diffing animation.
+    public func apply(_ snapshot: DiffableDataSourceSnapshot<SectionIdentifierType, ItemIdentifierType>, animatingDifferences: Bool = true) {
+        core.apply(
+            snapshot,
+            view: collectionView,
+            animatingDifferences: animatingDifferences,
+            performUpdates: { collectionView, changeset, setSections in
+                collectionView.reload(using: changeset, setData: setSections)
+        })
+    }
+
+    /// Returns a new snapshot object of current state.
+    ///
+    /// - Returns: A new snapshot object of current state.
+    public func snapshot() -> DiffableDataSourceSnapshot<SectionIdentifierType, ItemIdentifierType> {
+        return core.snapshot()
+    }
+
+    /// Returns an item identifier for given index path.
+    ///
+    /// - Parameters:
+    ///   - indexPath: An index path for the item identifier.
+    ///
+    /// - Returns: An item identifier for given index path.
+    public func itemIdentifier(for indexPath: IndexPath) -> ItemIdentifierType? {
+        return core.itemIdentifier(for: indexPath)
+    }
+
+    /// Returns an index path for given item identifier.
+    ///
+    /// - Parameters:
+    ///   - itemIdentifier: An identifier of item.
+    ///
+    /// - Returns: An index path for given item identifier.
+    public func indexPath(for itemIdentifier: ItemIdentifierType) -> IndexPath? {
+        return core.indexPath(for: itemIdentifier)
+    }
+
+    /// Returns the number of sections in the data source.
+    ///
+    /// - Parameters:
+    ///   - collectionView: A collection view instance managed by `self`.
+    ///
+    /// - Returns: The number of sections in the data source.
+    public func numberOfSections(in collectionView: UICollectionView) -> Int {
+        return core.numberOfSections()
+    }
+
+    /// Returns the number of items in the specified section.
+    ///
+    /// - Parameters:
+    ///   - collectionView: A collection view instance managed by `self`.
+    ///   - section: An index of section.
+    ///
+    /// - Returns: The number of items in the specified section.
+    public func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
+        return core.numberOfItems(inSection: section)
+    }
+
+    /// Returns a cell for item at specified index path.
+    ///
+    /// - Parameters:
+    ///   - collectionView: A collection view instance managed by `self`.
+    ///   - indexPath: An index path for cell.
+    ///
+    /// - Returns: A cell for row at specified index path.
+    open func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
+        let itemIdentifier = core.unsafeItemIdentifier(for: indexPath)
+        guard let cell = cellProvider(collectionView, indexPath, itemIdentifier) else {
+            universalError("UICollectionView dataSource returned a nil cell for item at index path: \(indexPath), collectionView: \(collectionView), itemIdentifier: \(itemIdentifier)")
+        }
+
+        return cell
+    }
+
+    /// Returns a supplementary view for element of kind at specified index path.
+    ///
+    /// - Parameters:
+    ///   - collectionView: A collection view instance managed by `self`.
+    ///   - kind: The kind of element to be display.
+    ///   - indexPath: An index path for supplementary view.
+    ///
+    /// - Returns: A supplementary view for element of kind at specified index path.
+    open func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
+        guard let view = supplementaryViewProvider?(collectionView, kind, indexPath) else {
+            return UICollectionReusableView()
+        }
+
+        return view
+    }
+}
+
+#endif