ios: fix switching to another chat prevents marking items as unread (#4652)

apps/ios/Shared/Model/ChatModel.swift

@@ -910,6 +910,12 @@ final class Chat: ObservableObject, Identifiable, ChatLike {
             chatStats: chatStats ?? self.chatStats
         )
     }
+    
+    func copyFrom(_ c: Chat) {
+        self.chatInfo = c.chatInfo
+        self.chatItems = c.chatItems
+        self.chatStats = c.chatStats
+    }
 
     var userCanSend: Bool {
         switch chatInfo {

apps/ios/Shared/Views/Chat/ChatView.swift

@@ -21,6 +21,7 @@ struct ChatView: View {
     @Environment(\.colorScheme) var colorScheme
     @Environment(\.presentationMode) var presentationMode
     @Environment(\.scenePhase) var scenePhase
+    // chat cannot be assigned, as it breaks observation in chat items
     @State @ObservedObject var chat: Chat
     @StateObject private var scrollModel = ReverseListScrollModel<ChatItem>()
     @StateObject private var floatingButtonModel = FloatingButtonModel()
@@ -141,7 +142,8 @@ struct ChatView: View {
             if let cId {
                 selectedChatItems = nil
                 if let c = chatModel.getChat(cId) {
-                    chat = c
+                    // chat cannot be assigned, as it breaks observation in chat items
+                    chat.copyFrom(c)
                 }
                 initChatView()
                 theme = buildTheme()
@@ -407,7 +409,8 @@ struct ChatView: View {
             }
             .onChange(of: chatModel.chatId) { chatId in
                 if let chatId, let c = chatModel.getChat(chatId) {
-                    chat = c
+                    // chat cannot be assigned, as it breaks observation in chat items
+                    chat.copyFrom(c)
                     showChatInfoSheet = false
                     loadChat(chat: c)
                 }