adding item moves to collection updates

Author: icanzilb

Example/Example/CollectionViewController.swift

@@ -36,7 +36,7 @@ class CollectionViewController: UIViewController {
     [Person(name: "Jim"), Person(name: "Jane")],
   ]
   let second = [
-    [Person(name: "Pete")],
+    [Person(name: "Pete"), Person(name: "Vicki")],
     [Person(name: "Jim")],
   ]
 

Example/Example/GitHubSearchViewController.swift

@@ -7,7 +7,7 @@ import UIKit
 import Combine
 import CombineDataSources
 
-struct Repo: Codable, Equatable {
+struct Repo: Codable, Hashable {
   let name: String
   let description: String?
 }

Example/Example/ViewController.swift

@@ -7,7 +7,7 @@ import UIKit
 import Combine
 import CombineDataSources
 
-struct Person: Equatable {
+struct Person: Hashable {
   let name: String
 }
 
@@ -28,10 +28,10 @@ class ViewController: UIViewController {
   // Test data set to use
   let first = [
     [Person(name: "Julia"), Person(name: "Vicki"), Person(name: "Pete")],
-    [Person(name: "Jim"), Person(name: "Jane")],
+    [Person(name: "Jane"), Person(name: "Jim")],
   ]
   let second = [
-    [Person(name: "Vicki")],
+    [Person(name: "Pete"), Person(name: "Vicki")],
     [Person(name: "Jim")],
   ]
 

Sources/CombineDataSources/CollectionViewItemsController.swift

@@ -11,10 +11,10 @@ import Combine
 public class CollectionViewItemsController<CollectionType>: NSObject, UICollectionViewDataSource
   where CollectionType: RandomAccessCollection,
   CollectionType.Index == Int,
-  CollectionType.Element: Equatable,
+  CollectionType.Element: Hashable,
   CollectionType.Element: RandomAccessCollection,
   CollectionType.Element.Index == Int,
-  CollectionType.Element.Element: Equatable {
+  CollectionType.Element.Element: Hashable {
 
   public typealias Element = CollectionType.Element.Element
   public typealias CellFactory<Element: Equatable> = (CollectionViewItemsController<CollectionType>, UICollectionView, IndexPath, Element) -> UICollectionViewCell
@@ -63,35 +63,19 @@ public class CollectionViewItemsController<CollectionType>: NSObject, UICollecti
     // Commit the changes to the collection view sections
     collectionView.performBatchUpdates({[unowned self] in
       for sectionIndex in 0..<items.count {
+        let rowAtIndex = self.fromRow(sectionIndex)
         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)))
+        
+        collectionView.deleteItems(at: changes.removals.map(rowAtIndex))
+        collectionView.insertItems(at: changes.insertions.map(rowAtIndex))
+        for move in changes.moves {
+          collectionView.moveItem(at: rowAtIndex(move.0), to: rowAtIndex(move.1))
+        }
       }
       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 }

Sources/CombineDataSources/Section.swift

@@ -13,7 +13,7 @@ public protocol SectionProtocol {
   var items: [Element] { get }
 }
 
-public struct Section<Element: Equatable>: SectionProtocol, Identifiable {
+public struct Section<Element: Hashable>: SectionProtocol, Identifiable {
   public init(header: String? = nil, items: [Element], footer: String? = nil, id: String? = nil) {
     self.id = id ?? header ?? UUID().uuidString
     self.header = header
@@ -34,6 +34,12 @@ extension Section: Equatable {
   }
 }
 
+extension Section: Hashable {
+  public func hash(into hasher: inout Hasher) {
+    hasher.combine(id)
+  }
+}
+
 extension Section: RandomAccessCollection {
   public var startIndex: Int {
     return items.startIndex

Sources/CombineDataSources/TableViewItemsController.swift

@@ -11,10 +11,10 @@ import Combine
 public class TableViewItemsController<CollectionType>: NSObject, UITableViewDataSource
   where CollectionType: RandomAccessCollection,
   CollectionType.Index == Int,
-  CollectionType.Element: Equatable,
+  CollectionType.Element: Hashable,
   CollectionType.Element: RandomAccessCollection,
   CollectionType.Element.Index == Int,
-  CollectionType.Element.Element: Equatable {
+  CollectionType.Element.Element: Hashable {
 
   public typealias Element = CollectionType.Element.Element
   public typealias CellFactory<Element: Equatable> = (TableViewItemsController<CollectionType>, UITableView, IndexPath, Element) -> UITableViewCell
@@ -70,35 +70,18 @@ public class TableViewItemsController<CollectionType>: NSObject, UITableViewData
     // Commit the changes to the table view sections
     tableView.beginUpdates()
     for sectionIndex in 0..<items.count {
+      let rowAtIndex = fromRow(sectionIndex)
       let changes = delta(newList: items[sectionIndex], oldList: collection[sectionIndex])
-      tableView.deleteRows(at: changes.removals.map(fromRow(sectionIndex)), with: rowAnimations.delete)
-      tableView.insertRows(at: changes.insertions.map(fromRow(sectionIndex)), with: rowAnimations.insert)
+      tableView.deleteRows(at: changes.removals.map(rowAtIndex), with: rowAnimations.delete)
+      tableView.insertRows(at: changes.insertions.map(rowAtIndex), with: rowAnimations.insert)
+      for move in changes.moves {
+        tableView.moveRow(at: rowAtIndex(move.0), to: rowAtIndex(move.1))
+      }
     }
     collection = items
     tableView.endUpdates()
   }
 
-  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 tableView: UITableView) -> Int {
     guard collection != nil else { return 0 }
@@ -132,3 +115,29 @@ public class TableViewItemsController<CollectionType>: NSObject, UITableViewData
     return dataSource
   }
 }
+
+internal func delta<T>(newList: T, oldList: T) -> (insertions: [Int], removals: [Int], moves: [(Int, Int)])
+  where T: RandomAccessCollection, T.Element: Hashable {
+    
+    let changes = newList.difference(from: oldList).inferringMoves()
+    
+    var insertions = [Int]()
+    var removals = [Int]()
+    var moves = [(Int, Int)]()
+    
+    for change in changes {
+      switch change {
+      case .insert(offset: let index, element: _, associatedWith: let associatedIndex):
+        if let fromIndex = associatedIndex {
+          moves.append((fromIndex, index))
+        } else {
+          insertions.append(index)
+        }
+      case .remove(offset: let index, element: _, associatedWith: let associatedIndex):
+        if associatedIndex == nil {
+          removals.append(index)
+        }
+      }
+    }
+    return (insertions: insertions, removals: removals, moves: moves)
+}