Added processOnlyVisibleItemsOnAnimatedBatchUpdates for a finer control over animation process.

Author: ekazaev

.jazzy.yaml

@@ -17,7 +17,6 @@ custom_categories:
       - ChatLayoutInvalidationContext
       - ItemKind
       - ItemSize
-      - ItemSize.CaseType
       - ChatItemAlignment
       - InitialAttributesRequestType
 

ChatLayout.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name             = 'ChatLayout'
-  s.version          = '1.2.13'
+  s.version          = '1.2.14'
   s.summary          = 'Chat UI Library. It uses custom UICollectionViewLayout to provide you full control over the presentation.'
   s.swift_version    = '5.7'
 

ChatLayout/Classes/Core/CollectionViewChatLayout.swift

@@ -23,6 +23,8 @@ import UIKit
 ///
 /// `CollectionViewChatLayout.keepContentOffsetAtBottomOnBatchUpdates`
 ///
+/// `CollectionViewChatLayout.processOnlyVisibleItemsOnAnimatedBatchUpdates`
+///
 /// `CollectionViewChatLayout.visibleBounds`
 ///
 /// `CollectionViewChatLayout.layoutFrame`
@@ -58,6 +60,15 @@ public final class CollectionViewChatLayout: UICollectionViewLayout {
     /// the animation starts and wont be able to compensate that change too. It should be done manually.
     public var keepContentOffsetAtBottomOnBatchUpdates: Bool = false
 
+    /// Sometimes `UIScrollView` can behave weirdly if there are too many corrections in it's `contentOffset` during the animation. Especially when content size of the `UIScrollView`
+    // is getting smaller first and then expands again as the newly appearing cells sizes are being calculated. That is why `CollectionViewChatLayout`
+    /// tries to process only the elements that are currently visible on the screen. But often it is not needed. This flag allows you to have fine control over this behaviour.
+    /// It set to `true` by default to keep the compatibility with the older versions of the library.
+    ///
+    /// **NB:**
+    /// This flag is only to provide fine control over the batch updates. If in doubts - keep it `true`.
+    public var processOnlyVisibleItemsOnAnimatedBatchUpdates: Bool = true
+
     /// Represent the currently visible rectangle.
     public var visibleBounds: CGRect {
         guard let collectionView = collectionView else {

ChatLayout/Classes/Core/Model/StateController.swift

@@ -28,6 +28,8 @@ protocol ChatLayoutRepresentation: AnyObject {
 
     var keepContentOffsetAtBottomOnBatchUpdates: Bool { get }
 
+    var processOnlyVisibleItemsOnAnimatedBatchUpdates: Bool { get }
+
     func numberOfItems(in section: Int) -> Int
 
     func configuration(for element: ItemKind, at indexPath: IndexPath) -> ItemModel.Configuration
@@ -764,7 +766,7 @@ final class StateController<Layout: ChatLayoutRepresentation> {
                         let itemPath = ItemPath(item: itemIndex, section: sectionIndex)
                         if let itemFrame = itemFrame(for: itemPath, kind: .cell, at: state, isFinal: true, additionalAttributes: additionalAttributes),
                            check(rect: itemFrame) {
-                            if state == .beforeUpdate || isAnimatedBoundsChange {
+                            if state == .beforeUpdate || isAnimatedBoundsChange || !layoutRepresentation.processOnlyVisibleItemsOnAnimatedBatchUpdates {
                                 allRects.append((frame: itemFrame, indexPath: itemPath, kind: .cell))
                             } else {
                                 var itemWasVisibleBefore: Bool {

ChatLayout/Classes/Extras/EdgeAligningView.swift

@@ -147,7 +147,8 @@ public final class EdgeAligningView<CustomView: UIView>: UIView {
             let layoutConstraint = view.centerXAnchor.constraint(equalTo: layoutMarginsGuide.centerXAnchor)
             addedConstraints.append(layoutConstraint)
             layoutConstraint.isActive = true
-        } else if flexibleEdges.contains(.top), flexibleEdges.contains(.bottom) {
+        }
+        if flexibleEdges.contains(.top), flexibleEdges.contains(.bottom) {
             let layoutConstraint = view.centerYAnchor.constraint(equalTo: layoutMarginsGuide.centerYAnchor)
             addedConstraints.append(layoutConstraint)
             layoutConstraint.isActive = true

Example/ChatLayout/Chat/Controller/ChatControllerDelegate.swift

@@ -14,6 +14,6 @@ import Foundation
 
 protocol ChatControllerDelegate: AnyObject {
 
-    func update(with sections: [Section])
+    func update(with sections: [Section], requiresIsolatedProcess: Bool)
 
 }

Example/ChatLayout/Chat/Controller/DefaultChatController.swift

@@ -193,9 +193,9 @@ final class DefaultChatController: ChatController {
         }
     }
 
-    private func repopulateMessages() {
+    private func repopulateMessages(requiresIsolatedProcess: Bool = false) {
         propagateLatestMessages { sections in
-            self.delegate?.update(with: sections)
+            self.delegate?.update(with: sections, requiresIsolatedProcess: requiresIsolatedProcess)
         }
     }
 
@@ -305,7 +305,7 @@ extension DefaultChatController: EditingAccessoryControllerDelegate {
 
     func deleteMessage(with id: UUID) {
         messages = Array(messages.filter { $0.id != id })
-        repopulateMessages()
+        repopulateMessages(requiresIsolatedProcess: true)
     }
 
 }

Example/ChatLayout/Chat/View/ChatViewController.swift

@@ -32,6 +32,7 @@ final class ChatViewController: UIViewController {
         case scrollingToBottom
         case showingPreview
         case showingAccessory
+        case updatingCollectionInIsolation
     }
 
     private enum ControllerActions {
@@ -124,6 +125,7 @@ final class ChatViewController: UIViewController {
         chatLayout.settings.interSectionSpacing = 8
         chatLayout.settings.additionalInsets = UIEdgeInsets(top: 8, left: 5, bottom: 8, right: 5)
         chatLayout.keepContentOffsetAtBottomOnBatchUpdates = true
+        chatLayout.processOnlyVisibleItemsOnAnimatedBatchUpdates = false
 
         collectionView = UICollectionView(frame: view.frame, collectionViewLayout: chatLayout)
         view.addSubview(collectionView)
@@ -156,7 +158,7 @@ final class ChatViewController: UIViewController {
         currentControllerActions.options.insert(.loadingInitialMessages)
         chatController.loadInitialMessages { sections in
             self.currentControllerActions.options.remove(.loadingInitialMessages)
-            self.processUpdates(with: sections, animated: true)
+            self.processUpdates(with: sections, animated: true, requiresIsolatedProcess: false)
         }
 
         KeyboardListener.shared.add(delegate: self)
@@ -298,7 +300,7 @@ extension ChatViewController: UIScrollViewDelegate {
             }
             // Reloading the content without animation just because it looks better is the scrolling is in process.
             let animated = !self.isUserInitiatedScrolling
-            self.processUpdates(with: sections, animated: animated) {
+            self.processUpdates(with: sections, animated: animated, requiresIsolatedProcess: false) {
                 self.currentControllerActions.options.remove(.loadingPreviousMessages)
             }
         }
@@ -441,11 +443,11 @@ extension ChatViewController: UICollectionViewDelegate {
 
 extension ChatViewController: ChatControllerDelegate {
 
-    func update(with sections: [Section]) {
-        processUpdates(with: sections, animated: true)
+    func update(with sections: [Section], requiresIsolatedProcess: Bool) {
+        processUpdates(with: sections, animated: true, requiresIsolatedProcess: requiresIsolatedProcess)
     }
 
-    private func processUpdates(with sections: [Section], animated: Bool = true, completion: (() -> Void)? = nil) {
+    private func processUpdates(with sections: [Section], animated: Bool = true, requiresIsolatedProcess: Bool, completion: (() -> Void)? = nil) {
         guard isViewLoaded else {
             dataSource.sections = sections
             return
@@ -459,7 +461,7 @@ extension ChatViewController: ChatControllerDelegate {
                                                                                        guard let self = self else {
                                                                                            return
                                                                                        }
-                                                                                       self.processUpdates(with: sections, animated: animated, completion: completion)
+                                                                                       self.processUpdates(with: sections, animated: animated, requiresIsolatedProcess: requiresIsolatedProcess, completion: completion)
                                                                                    })
             currentInterfaceActions.add(reaction: reaction)
             return
@@ -475,6 +477,10 @@ extension ChatViewController: ChatControllerDelegate {
                 return
             }
 
+            if requiresIsolatedProcess {
+                chatLayout.processOnlyVisibleItemsOnAnimatedBatchUpdates = true
+                currentInterfaceActions.options.insert(.updatingCollectionInIsolation)
+            }
             currentControllerActions.options.insert(.updatingCollection)
             collectionView.reload(using: changeSet,
                                   interrupt: { changeSet in
@@ -491,6 +497,10 @@ extension ChatViewController: ChatControllerDelegate {
                                   },
                                   completion: { _ in
                                       DispatchQueue.main.async {
+                                          self.chatLayout.processOnlyVisibleItemsOnAnimatedBatchUpdates = false
+                                          if requiresIsolatedProcess {
+                                              self.currentInterfaceActions.options.remove(.updatingCollectionInIsolation)
+                                          }
                                           completion?()
                                           self.currentControllerActions.options.remove(.updatingCollection)
                                       }
@@ -595,7 +605,7 @@ extension ChatViewController: InputBarAccessoryViewDelegate {
             self.scrollToBottom(completion: {
                 self.chatController.sendMessage(.text(messageText)) { sections in
                     self.currentInterfaceActions.options.remove(.sendingMessage)
-                    self.processUpdates(with: sections, animated: true)
+                    self.processUpdates(with: sections, animated: true, requiresIsolatedProcess: false)
                 }
             })
         }

Example/Podfile.lock

@@ -1,10 +1,10 @@
 PODS:
-  - ChatLayout (1.2.13):
-    - ChatLayout/Ultimate (= 1.2.13)
-  - ChatLayout/Core (1.2.13)
-  - ChatLayout/Extras (1.2.13):
+  - ChatLayout (1.2.14):
+    - ChatLayout/Ultimate (= 1.2.14)
+  - ChatLayout/Core (1.2.14)
+  - ChatLayout/Extras (1.2.14):
     - ChatLayout/Core
-  - ChatLayout/Ultimate (1.2.13):
+  - ChatLayout/Ultimate (1.2.14):
     - ChatLayout/Core
     - ChatLayout/Extras
   - DifferenceKit (1.3.0):
@@ -35,7 +35,7 @@ EXTERNAL SOURCES:
     :path: "../"
 
 SPEC CHECKSUMS:
-  ChatLayout: c37e188edd9a922d4c19d259703a29c63e0d18c6
+  ChatLayout: 0dabcfbceffa95f2a9a11c3bed1439457f89bc77
   DifferenceKit: ab185c4d7f9cef8af3fcf593e5b387fb81e999ca
   FPSCounter: 884afec377de66637808c4f52ecc3b85a404732b
   InputBarAccessoryView: 1d7b0a672b36e370f01f264b3907ef39d03328e3

Example/Tests/MockCollectionLayout.swift

@@ -45,6 +45,8 @@ class MockCollectionLayout: ChatLayoutRepresentation, ChatLayoutDelegate {
 
     let keepContentOffsetAtBottomOnBatchUpdates: Bool = true
 
+    let processOnlyVisibleItemsOnAnimatedBatchUpdates: Bool = true
+
     func numberOfItems(in section: Int) -> Int {
         numberOfItemsInSection[section] ?? 0
     }