Docs update

Sources/DiffableDataSource.CollectionView-UIKit.swift

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+//
+//  DiffableDataSource.CollectionView-UIKit.swift
+//  CoreStore
+//
+//  Copyright © 2018 John Rommel Estropia
+//
+//  Permission is hereby granted, free of charge, to any person obtaining a copy
+//  of this software and associated documentation files (the "Software"), to deal
+//  in the Software without restriction, including without limitation the rights
+//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//  copies of the Software, and to permit persons to whom the Software is
+//  furnished to do so, subject to the following conditions:
+//
+//  The above copyright notice and this permission notice shall be included in all
+//  copies or substantial portions of the Software.
+//
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+//  SOFTWARE.
+//
+
+#if canImport(UIKit) && (os(iOS) || os(tvOS))
+
+import UIKit
+import CoreData
+
+
+// MARK: - DiffableDataSource
+
+extension DiffableDataSource {
+
+    // MARK: - CollectionView
+    
+    /**
+     The `DiffableDataSource.CollectionView` serves as a `UICollectionViewDataSource` that handles `ListPublisher` snapshots for a `UICollectionView`. Subclasses of `DiffableDataSource.CollectionView` may override some `UICollectionViewDataSource` methods as needed.
+     The `DiffableDataSource.CollectionView` instance needs to be held on (retained) for as long as the `UICollectionView`'s lifecycle.
+     ```
+     self.dataSource = DiffableDataSource.CollectionView<Person>(
+         collectionView: self.collectionView,
+         dataStack: CoreStoreDefaults.dataStack,
+         cellProvider: { (collectionView, indexPath, person) in
+             let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "PersonCell") as! PersonCell
+             cell.setPerson(person)
+             return cell
+         }
+     )
+     ```
+     The dataSource can then apply changes from a `ListPublisher` as shown:
+     ```
+     listPublisher.addObserver(self) { [weak self] (listPublisher) in
+        self?.dataSource?.apply(
+            listPublisher.snapshot,
+            animatingDifferences: true
+        )
+     }
+     ```
+     `DiffableDataSource.CollectionView` fully handles the reload animations.
+     */
+    open class CollectionView<O: DynamicObject>: NSObject, UICollectionViewDataSource {
+
+        // MARK: Public
+        
+        /**
+         The object type represented by this dataSource
+         */
+        public typealias ObjectType = O
+        
+        /**
+         Initializes the `DiffableDataSource.CollectionView`. This instance needs to be held on (retained) for as long as the `UICollectionView`'s lifecycle.
+         ```
+         self.dataSource = DiffableDataSource.CollectionView<Person>(
+             collectionView: self.collectionView,
+             dataStack: CoreStoreDefaults.dataStack,
+             cellProvider: { (collectionView, indexPath, person) in
+                 let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "PersonCell") as! PersonCell
+                 cell.setPerson(person)
+                 return cell
+             }
+         )
+         ```
+         - parameter collectionView: the `UICollectionView` to set the `dataSource` of. This instance is not retained by the `DiffableDataSource.CollectionView`.
+         - parameter dataStack: the `DataStack` instance that the dataSource will fetch objects from
+         - parameter cellProvider: a closure that configures and returns the `UICollectionViewCell` for the object
+         - parameter supplementaryViewProvider: an optional closure for providing `UICollectionReusableView` supplementary views. If not set, defaults to returning `nil`
+         */
+        @nonobjc
+        public init(collectionView: UICollectionView, dataStack: DataStack, cellProvider: @escaping (UICollectionView, IndexPath, O) -> UICollectionViewCell?, supplementaryViewProvider: @escaping (UICollectionView, String, IndexPath) -> UICollectionReusableView? = { _, _, _ in nil }) {
+
+            self.collectionView = collectionView
+            self.cellProvider = cellProvider
+            self.supplementaryViewProvider = supplementaryViewProvider
+            self.dataStack = dataStack
+            self.dispatcher = Internals.DiffableDataUIDispatcher<O>(dataStack: dataStack)
+
+            super.init()
+
+            collectionView.dataSource = self
+        }
+        
+        /**
+         Reloads the `UICollectionView` using a `ListSnapshot`. This is typically from the `snapshot` property of a `ListPublisher`:
+         ```
+         listPublisher.addObserver(self) { [weak self] (listPublisher) in
+            self?.dataSource?.apply(
+                listPublisher.snapshot,
+                animatingDifferences: true
+            )
+         }
+         ```
+         
+         - parameter snapshot: the `ListSnapshot` used to reload the `UITableView` with. This is typically from the `snapshot` property of a `ListPublisher`.
+         - parameter animatingDifferences: if `true`, animations will be applied as configured by the `defaultRowAnimation` value. Defaults to `true`.
+         */
+        public func apply(_ snapshot: ListSnapshot<O>, animatingDifferences: Bool = true) {
+
+            let diffableSnapshot = snapshot.diffableSnapshot
+            self.dispatcher.apply(
+                diffableSnapshot as! Internals.DiffableDataSourceSnapshot,
+                view: self.collectionView,
+                animatingDifferences: animatingDifferences,
+                performUpdates: { collectionView, changeset, setSections in
+
+                    collectionView.reload(
+                        using: changeset,
+                        setData: setSections
+                    )
+                }
+            )
+        }
+        
+        /**
+         Returns the object identifier for the item at the specified `IndexPath`, or `nil` if not found
+         
+         - parameter indexPath: the `IndexPath` to search for
+         - returns: the object identifier for the item at the specified `IndexPath`, or `nil` if not found
+         */
+        @nonobjc
+        public func itemID(for indexPath: IndexPath) -> O.ObjectID? {
+
+            return self.dispatcher.itemIdentifier(for: indexPath)
+        }
+        
+        /**
+         Returns the `IndexPath` for the item with the specified object identifier, or `nil` if not found
+         
+         - parameter itemID: the object identifier to search for
+         - returns: the `IndexPath` for the item with the specified object identifier, or `nil` if not found
+         */
+        @nonobjc
+        public func indexPath(for itemID: O.ObjectID) -> IndexPath? {
+
+            return self.dispatcher.indexPath(for: itemID)
+        }
+
+
+        // MARK: - UICollectionViewDataSource
+
+        @objc
+        public dynamic func numberOfSections(in collectionView: UICollectionView) -> Int {
+
+            return self.dispatcher.numberOfSections()
+        }
+
+        @objc
+        public dynamic func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
+
+            return self.dispatcher.numberOfItems(inSection: section)
+        }
+
+        @objc
+        open dynamic func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
+
+            guard let objectID = self.dispatcher.itemIdentifier(for: indexPath) else {
+
+                Internals.abort("Object at \(Internals.typeName(IndexPath.self)) \(indexPath) already removed from list")
+            }
+            guard let object = self.dataStack.fetchExisting(objectID) as O? else {
+
+                Internals.abort("Object at \(Internals.typeName(IndexPath.self)) \(indexPath) has been deleted")
+            }
+            guard let cell = self.cellProvider(collectionView, indexPath, object) else {
+
+                Internals.abort("\(Internals.typeName(UICollectionViewDataSource.self)) returned a `nil` cell for \(Internals.typeName(IndexPath.self)) \(indexPath)")
+            }
+            return cell
+        }
+
+        @objc
+        open dynamic func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
+
+            guard let view = self.supplementaryViewProvider(collectionView, kind, indexPath) else {
+
+                return UICollectionReusableView()
+            }
+            return view
+        }
+
+
+        // MARK: Private
+
+        private weak var collectionView: UICollectionView?
+
+        private let dataStack: DataStack
+        private let cellProvider: (UICollectionView, IndexPath, O) -> UICollectionViewCell?
+        private let supplementaryViewProvider: (UICollectionView, String, IndexPath) -> UICollectionReusableView?
+        private let dispatcher: Internals.DiffableDataUIDispatcher<O>
+    }
+}
+
+
+// MARK: - UICollectionView
+
+extension UICollectionView {
+
+    // MARK: FilePrivate
+
+    @nonobjc
+    fileprivate func reload<C, O>(
+        using stagedChangeset: Internals.DiffableDataUIDispatcher<O>.StagedChangeset<C>,
+        interrupt: ((Internals.DiffableDataUIDispatcher<O>.Changeset<C>) -> Bool)? = nil,
+        setData: (C) -> Void
+    ) {
+
+        if case .none = window, let data = stagedChangeset.last?.data {
+
+            setData(data)
+            self.reloadData()
+            return
+        }
+        for changeset in stagedChangeset {
+
+            if let interrupt = interrupt, interrupt(changeset), let data = stagedChangeset.last?.data {
+
+                setData(data)
+                self.reloadData()
+                return
+            }
+            self.performBatchUpdates(
+                {
+                    setData(changeset.data)
+
+                    if !changeset.sectionDeleted.isEmpty {
+
+                        self.deleteSections(IndexSet(changeset.sectionDeleted))
+                    }
+                    if !changeset.sectionInserted.isEmpty {
+
+                        self.insertSections(IndexSet(changeset.sectionInserted))
+                    }
+                    if !changeset.sectionUpdated.isEmpty {
+
+                        self.reloadSections(IndexSet(changeset.sectionUpdated))
+                    }
+                    for (source, target) in changeset.sectionMoved {
+
+                        self.moveSection(source, toSection: target)
+                    }
+                    if !changeset.elementDeleted.isEmpty {
+
+                        self.deleteItems(
+                            at: changeset.elementDeleted.map { IndexPath(item: $0.element, section: $0.section) }
+                        )
+                    }
+                    if !changeset.elementInserted.isEmpty {
+
+                        self.insertItems(
+                            at: changeset.elementInserted.map { IndexPath(item: $0.element, section: $0.section) }
+                        )
+                    }
+                    if !changeset.elementUpdated.isEmpty {
+
+                        self.reloadItems(
+                            at: changeset.elementUpdated.map { IndexPath(item: $0.element, section: $0.section) }
+                        )
+                    }
+                    for (source, target) in changeset.elementMoved {
+
+                        self.moveItem(
+                            at: IndexPath(item: source.element, section: source.section),
+                            to: IndexPath(item: target.element, section: target.section)
+                        )
+                    }
+                },
+                completion: nil
+            )
+        }
+    }
+}
+
+
+#endif