Channel list performance improvements

Author: martinmitrevski

Sources/StreamChatSwiftUI/ChatChannelList/ChannelHeaderLoader.swift

@@ -17,6 +17,9 @@ open class ChannelHeaderLoader: ObservableObject {
     /// Prevents image requests to be executed if they failed previously.
     private var failedImageLoads = Set<String>()
 
+    /// Batches loaded images for update, to improve performance.
+    private var scheduledUpdate = false
+
     /// Context provided utils.
     internal lazy var imageLoader = utils.imageLoader
     internal lazy var imageCDN = utils.imageCDN
@@ -29,7 +32,17 @@ open class ChannelHeaderLoader: ObservableObject {
     internal lazy var placeholder3 = images.userAvatarPlaceholder3
     internal lazy var placeholder4 = images.userAvatarPlaceholder4
 
-    @Published var loadedImages = [String: UIImage]()
+    var loadedImages = [String: UIImage]() {
+        willSet {
+            if !scheduledUpdate {
+                scheduledUpdate = true
+                DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) { [weak self] in
+                    self?.objectWillChange.send()
+                    self?.scheduledUpdate = false
+                }
+            }
+        }
+    }
 
     public init() {}
 
@@ -38,7 +51,7 @@ open class ChannelHeaderLoader: ObservableObject {
     /// - Parameter channel: the provided channel.
     /// - Returns: the available image.
     public func image(for channel: ChatChannel) -> UIImage {
-        if let image = loadedImages[channel.cid.id] {
+        if let image = loadedImages[channel.cid.rawValue] {
             return image
         }
 
@@ -78,6 +91,10 @@ open class ChannelHeaderLoader: ObservableObject {
     // MARK: - private
 
     private func loadMergedAvatar(from channel: ChatChannel, urls: [URL]) {
+        if failedImageLoads.contains(channel.cid.rawValue) {
+            return
+        }
+        
         imageLoader.loadImages(
             from: urls,
             placeholders: [],
@@ -87,9 +104,13 @@ open class ChannelHeaderLoader: ObservableObject {
         ) { [weak self] images in
             guard let self = self else { return }
             DispatchQueue.global(qos: .userInteractive).async {
-                let image = self.channelAvatarsMerger.createMergedAvatar(from: images) ?? self.placeholder2
+                let image = self.channelAvatarsMerger.createMergedAvatar(from: images)
                 DispatchQueue.main.async {
-                    self.loadedImages[channel.cid.id] = image
+                    if let image = image {
+                        self.loadedImages[channel.cid.rawValue] = image
+                    } else {
+                        self.failedImageLoads.insert(channel.cid.rawValue)
+                    }
                 }
             }
         }
@@ -99,7 +120,7 @@ open class ChannelHeaderLoader: ObservableObject {
         for channel: ChatChannel,
         from url: URL
     ) {
-        if failedImageLoads.contains(channel.cid.id) {
+        if failedImageLoads.contains(channel.cid.rawValue) {
             return
         }
 
@@ -113,10 +134,10 @@ open class ChannelHeaderLoader: ObservableObject {
             switch result {
             case let .success(image):
                 DispatchQueue.main.async {
-                    self.loadedImages[channel.cid.id] = image
+                    self.loadedImages[channel.cid.rawValue] = image
                 }
             case let .failure(error):
-                self.failedImageLoads.insert(channel.cid.id)
+                self.failedImageLoads.insert(channel.cid.rawValue)
                 log.error("error loading image: \(error.localizedDescription)")
             }
         }

Sources/StreamChatSwiftUI/ChatChannelList/ChatChannelList.swift

@@ -176,7 +176,7 @@ extension ChatChannel: Identifiable {
     }
 
     public var id: String {
-        "\(cid.id)-\(lastMessageAt ?? createdAt)-\(lastActiveMembersCount)-\(mutedString)-\(unreadCount.messages)-\(typingUsersString)-\(readUsersId)"
+        "\(cid.id)-\(lastMessageAt ?? createdAt)-\(lastActiveMembersCount)-\(mutedString)-\(typingUsersString)-\(readUsersId)"
     }
 
     private var readUsersId: String {

Sources/StreamChatSwiftUI/ChatChannelList/ChatChannelListViewModel.swift

@@ -123,16 +123,15 @@ open class ChatChannelListViewModel: ObservableObject, ChatChannelListController
     ///
     /// - Parameter index: the currently displayed index.
     public func checkForChannels(index: Int) {
-        if index < (controller?.channels.count ?? 0) - 10 {
+        if index < (controller?.channels.count ?? 0) - 15 {
             return
         }
 
         if !loadingNextChannels {
             loadingNextChannels = true
-            controller?.loadNextChannels { [weak self] _ in
+            controller?.loadNextChannels(limit: 30) { [weak self] _ in
                 guard let self = self else { return }
                 self.loadingNextChannels = false
-                self.updateChannels()
             }
         }
     }
@@ -194,10 +193,6 @@ open class ChatChannelListViewModel: ObservableObject, ChatChannelListController
 
     // MARK: - ChatChannelListControllerDelegate
 
-    public func controllerWillChangeChannels(_ controller: ChatChannelListController) {
-        handleChannelListChanges(controller)
-    }
-    
     public func controller(
         _ controller: ChatChannelListController,
         didChangeChannels changes: [ListChange<ChatChannel>]

Sources/StreamChatSwiftUI/ChatChannelList/ChatChannelSwipeableListItem.swift

@@ -151,7 +151,9 @@ public struct ChatChannelSwipeableListItem<Factory: ViewFactory, ChannelListItem
         }
 
         if horizontalTranslation != 0 {
-            swipedChannelId = channel.id
+            if swipedChannelId != channel.id {
+                swipedChannelId = channel.id
+            }
             offsetX = horizontalTranslation
         } else {
             offsetX = 0

StreamChatSwiftUITests/Tests/ChatChannelList/ChatChannelListViewModel_Tests.swift

@@ -60,7 +60,7 @@ class ChatChannelListViewModel_Tests: StreamChatTestCase {
     func test_channelListVM_onChannelAppear_loadNextChannelsNotCalled() {
         // Given
         var channels = [ChatChannel]()
-        for _ in 0..<15 {
+        for _ in 0..<20 {
             channels.append(ChatChannel.mockDMChannel())
         }
         let channelListController = makeChannelListController(channels: channels)