Merge pull request #75 from diegosanchezr/dev

Allows customizing index paths to calculate offset after update

Chatto/Source/ChatController/BaseChatViewController+Changes.swift

@@ -118,7 +118,8 @@ extension BaseChatViewController: ChatDataSourceDelegateProtocol {
         updateType: UpdateType,
         completion: () -> Void) {
             let shouldScrollToBottom = updateType != .Pagination && self.isScrolledAtBottom()
-            let oldRect = self.rectAtIndexPath(changes.movedIndexPaths.first?.indexPathOld)
+            let (oldReferenceIndexPath, newReferenceIndexPath) = self.referenceIndexPathsToRestoreScrollPositionOnUpdate(itemsBeforeUpdate: self.chatItemCompanionCollection, changes: changes)
+            let oldRect = self.rectAtIndexPath(oldReferenceIndexPath)
             let myCompletion = {
                 // Found that cells may not match correct index paths here yet! (see comment below)
                 // Waiting for next loop seems to fix the issue
@@ -156,7 +157,7 @@ extension BaseChatViewController: ChatDataSourceDelegateProtocol {
             if shouldScrollToBottom {
                 self.scrollToBottom(animated: updateType == .Normal)
             } else {
-                let newRect = self.rectAtIndexPath(changes.movedIndexPaths.first?.indexPathNew)
+                let newRect = self.rectAtIndexPath(newReferenceIndexPath)
                 self.scrollToPreservePosition(oldRefRect: oldRect, newRefRect: newRect)
             }
     }

Chatto/Source/ChatController/BaseChatViewController.swift

@@ -187,16 +187,6 @@ public class BaseChatViewController: UIViewController, UICollectionViewDataSourc
     let presentersByCell = NSMapTable(keyOptions: .WeakMemory, valueOptions: .WeakMemory)
     var updateQueue: SerialTaskQueueProtocol = SerialTaskQueue()
 
-    public func createPresenterBuilders() -> [ChatItemType: [ChatItemPresenterBuilderProtocol]] {
-        assert(false, "Override in subclass")
-        return [ChatItemType: [ChatItemPresenterBuilderProtocol]]()
-    }
-
-    public func createChatInputView() -> UIView {
-        assert(false, "Override in subclass")
-        return UIView()
-    }
-
     /**
      - You can use a decorator to:
         - Provide the ChatCollectionViewLayout with margins between messages
@@ -212,6 +202,28 @@ public class BaseChatViewController: UIViewController, UICollectionViewDataSourc
     }
 
     var layoutModel = ChatCollectionViewLayoutModel.createModel(0, itemsLayoutData: [])
+
+
+    // MARK: Subclass overrides
+
+    public func createPresenterBuilders() -> [ChatItemType: [ChatItemPresenterBuilderProtocol]] {
+        assert(false, "Override in subclass")
+        return [ChatItemType: [ChatItemPresenterBuilderProtocol]]()
+    }
+
+    public func createChatInputView() -> UIView {
+        assert(false, "Override in subclass")
+        return UIView()
+    }
+
+    /**
+        When paginating up we need to change the scroll position as the content is pushed down.
+        We take distance to top from beforeUpdate indexPath and then we make afterUpdate indexPath to appear at the same distance
+    */
+    public func referenceIndexPathsToRestoreScrollPositionOnUpdate(itemsBeforeUpdate itemsBeforeUpdate: ChatItemCompanionCollection, changes: CollectionChanges) -> (beforeUpdate: NSIndexPath?, afterUpdate: NSIndexPath?) {
+        let firstItemMoved = changes.movedIndexPaths.first
+        return (firstItemMoved?.indexPathOld, firstItemMoved?.indexPathNew)
+    }
 }
 
 extension BaseChatViewController { // Rotation

Chatto/Source/ChatController/CollectionChanges.swift

@@ -28,25 +28,25 @@ public protocol UniqueIdentificable {
     var uid: String { get }
 }
 
-struct CollectionChangeMove: Equatable, Hashable {
-    let indexPathOld: NSIndexPath
-    let indexPathNew: NSIndexPath
-    init(indexPathOld: NSIndexPath, indexPathNew: NSIndexPath) {
+public struct CollectionChangeMove: Equatable, Hashable {
+    public let indexPathOld: NSIndexPath
+    public let indexPathNew: NSIndexPath
+    public init(indexPathOld: NSIndexPath, indexPathNew: NSIndexPath) {
         self.indexPathOld = indexPathOld
         self.indexPathNew = indexPathNew
     }
 
-    var hashValue: Int { return indexPathOld.hash ^ indexPathNew.hash }
+    public var hashValue: Int { return indexPathOld.hash ^ indexPathNew.hash }
 }
 
-func == (lhs: CollectionChangeMove, rhs: CollectionChangeMove) -> Bool {
+public func == (lhs: CollectionChangeMove, rhs: CollectionChangeMove) -> Bool {
     return lhs.indexPathOld == rhs.indexPathOld && lhs.indexPathNew == rhs.indexPathNew
 }
 
-struct CollectionChanges {
-    let insertedIndexPaths: Set<NSIndexPath>
-    let deletedIndexPaths: Set<NSIndexPath>
-    let movedIndexPaths: [CollectionChangeMove]
+public struct CollectionChanges {
+    public let insertedIndexPaths: Set<NSIndexPath>
+    public let deletedIndexPaths: Set<NSIndexPath>
+    public let movedIndexPaths: [CollectionChangeMove]
 
     init(insertedIndexPaths: Set<NSIndexPath>, deletedIndexPaths: Set<NSIndexPath>, movedIndexPaths: [CollectionChangeMove]) {
         self.insertedIndexPaths = insertedIndexPaths