adding collection view support

Author: icanzilb

Example/Example.xcodeproj/project.pbxproj

@@ -7,6 +7,7 @@
 	objects = {
 
 /* Begin PBXBuildFile section */
+		9C326989230B2DDE00E93F9C /* CollectionViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9C326988230B2DDE00E93F9C /* CollectionViewController.swift */; };
 		9C371EE7230356CE00617B57 /* MenuTableViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9C371EE6230356CE00617B57 /* MenuTableViewController.swift */; };
 		9CA4B70D23048B470041CBA4 /* GitHubSearchViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9CA4B70C23048B470041CBA4 /* GitHubSearchViewController.swift */; };
 		9CB630CA22FD510000368A0D /* AppDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9CB630C922FD510000368A0D /* AppDelegate.swift */; };
@@ -19,6 +20,7 @@
 /* End PBXBuildFile section */
 
 /* Begin PBXFileReference section */
+		9C326988230B2DDE00E93F9C /* CollectionViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CollectionViewController.swift; sourceTree = "<group>"; };
 		9C371EE6230356CE00617B57 /* MenuTableViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MenuTableViewController.swift; sourceTree = "<group>"; };
 		9CA4B70C23048B470041CBA4 /* GitHubSearchViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = GitHubSearchViewController.swift; sourceTree = "<group>"; };
 		9CB630C622FD510000368A0D /* Example.app */ = {isa = PBXFileReference; explicitFileType = wrapper.application; includeInIndex = 0; path = Example.app; sourceTree = BUILT_PRODUCTS_DIR; };
@@ -69,6 +71,7 @@
 				9CB630CB22FD510000368A0D /* SceneDelegate.swift */,
 				9C371EE6230356CE00617B57 /* MenuTableViewController.swift */,
 				9CB630CD22FD510000368A0D /* ViewController.swift */,
+				9C326988230B2DDE00E93F9C /* CollectionViewController.swift */,
 				9CA4B70C23048B470041CBA4 /* GitHubSearchViewController.swift */,
 				9CB630CF22FD510000368A0D /* Main.storyboard */,
 				9CB630D222FD510100368A0D /* Assets.xcassets */,
@@ -160,6 +163,7 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				9C326989230B2DDE00E93F9C /* CollectionViewController.swift in Sources */,
 				9C371EE7230356CE00617B57 /* MenuTableViewController.swift in Sources */,
 				9CB630CE22FD510000368A0D /* ViewController.swift in Sources */,
 				9CA4B70D23048B470041CBA4 /* GitHubSearchViewController.swift in Sources */,

Example/Example/Base.lproj/Main.storyboard

@@ -0,0 +1,106 @@
+//
+//  For credits and licence check the LICENSE file included in this package.
+//  (c) CombineOpenSource, Created by Marin Todorov.
+//
+
+import UIKit
+import Combine
+import CombineDataSources
+
+class PersonCollectionCell: UICollectionViewCell {
+  @IBOutlet var nameLabel: UILabel!
+  @IBOutlet var image: UIImageView!
+  private var subscriptions = [AnyCancellable]()
+  
+  var imageURL: URL! {
+    didSet {
+      URLSession.shared.dataTaskPublisher(for: imageURL)
+        .compactMap { UIImage(data: $0.data) }
+        .replaceError(with: UIImage())
+        .receive(on: DispatchQueue.main)
+        .assign(to: \.image, on: image)
+        .store(in: &subscriptions)
+    }
+  }
+}
+
+class CollectionViewController: UIViewController {
+  @IBOutlet var collectionView: UICollectionView!
+  
+  // The kind of demo to show
+  var demo: Demo = .plain
+  
+  // Test data set to use
+  let first = [
+    [Person(name: "Julia"), Person(name: "Vicki"), Person(name: "Pete")],
+    [Person(name: "Jim"), Person(name: "Jane")],
+  ]
+  let second = [
+    [Person(name: "Pete")],
+    [Person(name: "Jim")],
+  ]
+  
+  // Publisher to emit data to the table
+  var data = PassthroughSubject<[[Person]], Never>()
+  
+  private var flag = false
+  
+  // Emits values out of `data`
+  func reload() {
+    data.send(flag ? first : second)
+    flag.toggle()
+    
+    DispatchQueue.main.asyncAfter(deadline: .now() + 1) { [weak self] in
+      self?.reload()
+    }
+  }
+
+  override func viewDidLoad() {
+    super.viewDidLoad()
+
+    switch demo {
+    case .plain:
+      // A plain list with a single section -> Publisher<[Person], Never>
+      data
+        .map { $0[0] }
+        .subscribe(collectionView.itemsSubscriber(cellIdentifier: "Cell", cellType: PersonCollectionCell.self, cellConfig: { cell, indexPath, model in
+          cell.nameLabel.text = model.name
+          cell.imageURL = URL(string: "https://api.adorable.io/avatars/100/\(model.name)")!
+        }))
+    
+    case .multiple:
+      // Table with sections -> Publisher<[[Person]], Never>
+      data
+        .subscribe(collectionView.sectionsSubscriber(cellIdentifier: "Cell", cellType: PersonCollectionCell.self, cellConfig: { cell, indexPath, model in
+          cell.nameLabel.text = model.name
+          cell.imageURL = URL(string: "https://api.adorable.io/avatars/100/\(model.name)")!
+        }))
+
+    case .sections:
+      // Table with section driven by `Section` models -> Publisher<[Section<Person>], Never>
+      data
+        .map { sections in
+          return sections.map { persons -> Section<Person> in
+            return Section(items: persons)
+          }
+        }
+        .subscribe(collectionView.sectionsSubscriber(cellIdentifier: "Cell", cellType: PersonCollectionCell.self, cellConfig: { cell, indexPath, model in
+          cell.nameLabel.text = model.name
+          cell.imageURL = URL(string: "https://api.adorable.io/avatars/100/\(model.name)")!
+        }))
+
+    case .noAnimations:
+      // Use custom controller to disable animations
+      let controller = CollectionViewItemsController<[[Person]]>(cellIdentifier: "Cell", cellType: PersonCollectionCell.self) { cell, indexPath, person in
+        cell.nameLabel.text = person.name
+        cell.imageURL = URL(string: "https://api.adorable.io/avatars/100/\(person.name)")!
+      }
+      controller.animated = false
+      
+      data
+        .subscribe(collectionView.sectionsSubscriber(controller))
+    }
+    
+    reload()
+  }
+}

Example/Example/CollectionViewController.swift

@@ -9,5 +9,6 @@ class MenuTableViewController: UITableViewController {
   override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
     let rowIndex = (sender as! UITableViewCell).tag
     (segue.destination as? ViewController)?.demo = Demo(rawValue: rowIndex)!
+    (segue.destination as? CollectionViewController)?.demo = Demo(rawValue: rowIndex)!
   }
 }

Example/Example/MenuTableViewController.swift

@@ -43,6 +43,18 @@ data
 
 ![Plain list updates with CombineDataSources](https://github.com/combineopensource/CombineDataSources/raw/master/Assets/plain-list.gif)
 
+Respectively for a collection view:
+
+```swift
+data
+  .subscribe(collectionView.itemsSubscriber(cellIdentifier: "Cell", cellType: PersonCollectionCell.self, cellConfig: { cell, indexPath, model in
+    cell.nameLabel.text = model.name
+    cell.imageURL = URL(string: "https://api.adorable.io/avatars/100/\(model.name)")!
+  }))
+```
+
+![Plain list updates for a collection view](https://github.com/combineopensource/CombineDataSources/raw/master/Assets/plain-collection.gif)
+
 #### Bind a list of Section models
 
 ```swift

README.md

@@ -0,0 +1,113 @@
+//
+//  For credits and licence check the LICENSE file included in this package.
+//  (c) CombineOpenSource, Created by Marin Todorov.
+//
+
+import UIKit
+import Combine
+
+/// A collection view controller acting as data source.
+/// `CollectionType` needs to be a collection of collections to represent sections containing rows.
+public class CollectionViewItemsController<CollectionType>: NSObject, UICollectionViewDataSource
+  where CollectionType: RandomAccessCollection,
+  CollectionType.Index == Int,
+  CollectionType.Element: Equatable,
+  CollectionType.Element: RandomAccessCollection,
+  CollectionType.Element.Index == Int,
+  CollectionType.Element.Element: Equatable {
+  
+  public typealias Element = CollectionType.Element.Element
+  public typealias CellFactory<Element: Equatable> = (CollectionViewItemsController<CollectionType>, UICollectionView, IndexPath, Element) -> UICollectionViewCell
+  public typealias CellConfig<Element, Cell> = (Cell, IndexPath, Element) -> Void
+  
+  private let cellFactory: CellFactory<Element>
+  private var collection: CollectionType!
+  
+  /// Should the table updates be animated or static.
+  public var animated = true
+  
+  /// The collection view for the data source
+  var collectionView: UICollectionView!
+  
+  /// A fallback data source to implement custom logic like indexes, dragging, etc.
+  public var dataSource: UICollectionViewDataSource?
+  
+  // MARK: - Init
+  public init<CellType>(cellIdentifier: String, cellType: CellType.Type, cellConfig: @escaping CellConfig<Element, CellType>) where CellType: UICollectionViewCell {
+    cellFactory = { dataSource, collectionView, indexPath, value in
+      let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellIdentifier, for: indexPath) as! CellType
+      cellConfig(cell, indexPath, value)
+      return cell
+    }
+  }
+  
+  private init(cellFactory: @escaping CellFactory<Element>) {
+    self.cellFactory = cellFactory
+  }
+  
+  deinit {
+    debugPrint("Controller is released")
+  }
+  
+  // MARK: - Update collection
+  private let fromRow = {(section: Int) in return {(row: Int) in return IndexPath(row: row, section: section)}}
+  
+  func updateCollection(_ items: CollectionType) {
+    // If the changes are not animatable, reload the table
+    guard animated, collection != nil, items.count == collection.count else {
+      collection = items
+      collectionView.reloadData()
+      return
+    }
+    
+    // Commit the changes to the collection view sections
+    collectionView.performBatchUpdates({[unowned self] in
+      for sectionIndex in 0..<items.count {
+        let changes = delta(newList: items[sectionIndex], oldList: collection[sectionIndex])
+        collectionView.deleteItems(at: changes.removals.map(self.fromRow(sectionIndex)))
+        collectionView.insertItems(at: changes.insertions.map(self.fromRow(sectionIndex)))
+      }
+      collection = items
+    }, completion: nil)
+  }
+  
+  private func delta<T>(newList: T, oldList: T) -> (insertions: [Int], removals: [Int])
+    where T: RandomAccessCollection, T.Element: Equatable {
+      
+      let changes = newList.difference(from: oldList)
+      
+      let insertIndexes = changes.compactMap { change -> Int? in
+        guard case CollectionDifference<T.Element>.Change.insert(let offset, _, _) = change else {
+          return nil
+        }
+        return offset
+      }
+      let deleteIndexes = changes.compactMap { change -> Int? in
+        guard case CollectionDifference<T.Element>.Change.remove(let offset, _, _) = change else {
+          return nil
+        }
+        return offset
+      }
+      
+      return (insertions: insertIndexes, removals: deleteIndexes)
+  }
+  
+  // MARK: - UITableViewDataSource protocol
+  public func numberOfSections(in collectionView: UICollectionView) -> Int {
+    guard collection != nil else { return 0 }
+    return collection.count
+  }
+  
+  public func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
+    return collection[section].count
+  }
+  
+  public func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
+    cellFactory(self, collectionView, indexPath, collection[indexPath.section][indexPath.row])
+  }
+  
+  // MARK: - Fallback data source object
+  override public func forwardingTarget(for aSelector: Selector!) -> Any? {
+    return dataSource
+  }
+}

Sources/CombineDataSources/CollectionViewItemsController.swift

@@ -0,0 +1,87 @@
+//
+//  For credits and licence check the LICENSE file included in this package.
+//  (c) CombineOpenSource, Created by Marin Todorov.
+//
+
+import UIKit
+import Combine
+
+extension UICollectionView {
+  
+  /// A collection view specific `Subscriber` that receives `[[Element]]` input and updates a sectioned collection view.
+  /// - Parameter cellIdentifier: The Cell ID to use for dequeueing table cells.
+  /// - Parameter cellType: The required cell type for table rows.
+  /// - Parameter cellConfig: A closure that receives an initialized cell and a collection element
+  ///     and configures the cell for displaying in its containing table view.
+  public func sectionsSubscriber<CellType, Items>(cellIdentifier: String, cellType: CellType.Type, cellConfig: @escaping CollectionViewItemsController<Items>.CellConfig<Items.Element.Element, CellType>)
+    -> AnySubscriber<Items, Never> where CellType: UICollectionViewCell,
+    Items: RandomAccessCollection,
+    Items.Element: RandomAccessCollection,
+    Items.Element: Equatable {
+      
+      return sectionsSubscriber(.init(cellIdentifier: cellIdentifier, cellType: cellType, cellConfig: cellConfig))
+  }
+  
+  /// A table view specific `Subscriber` that receives `[[Element]]` input and updates a sectioned table view.
+  /// - Parameter source: A configured `CollectionViewItemsController<Items>` instance.
+  public func sectionsSubscriber<Items>(_ source: CollectionViewItemsController<Items>)
+    -> AnySubscriber<Items, Never> where
+    Items: RandomAccessCollection,
+    Items.Element: RandomAccessCollection,
+    Items.Element: Equatable {
+      
+      source.collectionView = self
+      dataSource = source
+      
+      return AnySubscriber<Items, Never>(receiveSubscription: { subscription in
+        subscription.request(.unlimited)
+      }, receiveValue: { [weak self] items -> Subscribers.Demand in
+        guard let self = self else { return .none }
+        
+        if self.dataSource == nil {
+          self.dataSource = source
+        }
+        
+        source.updateCollection(items)
+        return .unlimited
+      }) { _ in }
+  }
+  
+  /// A table view specific `Subscriber` that receives `[Element]` input and updates a single section table view.
+  /// - Parameter cellIdentifier: The Cell ID to use for dequeueing table cells.
+  /// - Parameter cellType: The required cell type for table rows.
+  /// - Parameter cellConfig: A closure that receives an initialized cell and a collection element
+  ///     and configures the cell for displaying in its containing table view.
+  public func itemsSubscriber<CellType, Items>(cellIdentifier: String, cellType: CellType.Type, cellConfig: @escaping CollectionViewItemsController<[Items]>.CellConfig<Items.Element, CellType>)
+    -> AnySubscriber<Items, Never> where CellType: UICollectionViewCell,
+    Items: RandomAccessCollection,
+    Items: Equatable {
+      
+      return itemsSubscriber(.init(cellIdentifier: cellIdentifier, cellType: cellType, cellConfig: cellConfig))
+  }
+  
+  /// A table view specific `Subscriber` that receives `[Element]` input and updates a single section table view.
+  /// - Parameter source: A configured `CollectionViewItemsController<Items>` instance.
+  public func itemsSubscriber<Items>(_ source: CollectionViewItemsController<[Items]>)
+    -> AnySubscriber<Items, Never> where
+    Items: RandomAccessCollection,
+    Items: Equatable {
+      
+      source.collectionView = self
+      dataSource = source
+      
+      return AnySubscriber<Items, Never>(receiveSubscription: { subscription in
+        subscription.request(.unlimited)
+      }, receiveValue: { [weak self] items -> Subscribers.Demand in
+        guard let self = self else { return .none }
+        
+        if self.dataSource == nil {
+          self.dataSource = source
+        }
+        
+        source.updateCollection([items])
+        return .unlimited
+      }) { _ in }
+  }
+}
+