From 9d593bcaff33ec73d4608cafb458b56ebde3b5c8 Mon Sep 17 00:00:00 2001
From: Jeffrey Starke <jeffrey@signal.org>
Date: Thu, 24 Apr 2025 11:21:09 -0400
Subject: [PATCH] Fix chat folders flickering during drag and drop.

Fixes the UI flickering that occurs when reordering chat folders. The issue was caused by the ViewModel updating the database each time a list item position changes when we were already updating list order in the UI state manually at the same time.
---
 .../app/chats/folders/ChatFoldersFragment.kt  | 16 +++++++-----
 .../app/chats/folders/ChatFoldersViewModel.kt | 26 ++++++++++++-------
 2 files changed, 25 insertions(+), 17 deletions(-)

diff --git a/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/chats/folders/ChatFoldersFragment.kt b/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/chats/folders/ChatFoldersFragment.kt
index d430e8f0df..209e945b9d 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/chats/folders/ChatFoldersFragment.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/chats/folders/ChatFoldersFragment.kt
@@ -101,7 +101,13 @@ class ChatFoldersFragment : ComposeFragment() {
         onDeleteDismissed = {
           viewModel.showDeleteDialog(false)
         },
-        onPositionUpdated = { fromIndex, toIndex -> viewModel.updatePosition(fromIndex, toIndex) }
+        onDragAndDropEvent = { event ->
+          when (event) {
+            is DragAndDropEvent.OnItemMove -> viewModel.updateItemPosition(event.fromIndex, event.toIndex)
+            is DragAndDropEvent.OnItemDrop -> viewModel.saveItemPositions()
+            is DragAndDropEvent.OnDragCancel -> {}
+          }
+        }
       )
     }
   }
@@ -117,16 +123,12 @@ fun FoldersScreen(
   onDeleteClicked: (ChatFolderRecord) -> Unit = {},
   onDeleteConfirmed: () -> Unit = {},
   onDeleteDismissed: () -> Unit = {},
-  onPositionUpdated: (Int, Int) -> Unit = { _, _ -> }
+  onDragAndDropEvent: (DragAndDropEvent) -> Unit = {}
 ) {
   val screenWidth = LocalConfiguration.current.screenWidthDp.dp
   val isRtl = ViewUtil.isRtl(LocalContext.current)
   val listState = rememberLazyListState()
-  val dragDropState = rememberDragDropState(listState, includeHeader = true, includeFooter = true) { event ->
-    if (event is DragAndDropEvent.OnItemMove) {
-      onPositionUpdated(event.fromIndex, event.toIndex)
-    }
-  }
+  val dragDropState = rememberDragDropState(listState, includeHeader = true, includeFooter = true, onEvent = onDragAndDropEvent)
 
   LaunchedEffect(Unit) {
     if (!SignalStore.uiHints.hasSeenChatFoldersEducationSheet) {
diff --git a/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/chats/folders/ChatFoldersViewModel.kt b/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/chats/folders/ChatFoldersViewModel.kt
index 5912a604f5..897650b91d 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/chats/folders/ChatFoldersViewModel.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/chats/folders/ChatFoldersViewModel.kt
@@ -8,6 +8,7 @@ import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.launch
+import org.signal.core.util.swap
 import org.thoughtcrime.securesms.R
 import org.thoughtcrime.securesms.contacts.paged.ChatType
 import org.thoughtcrime.securesms.database.SignalDatabase
@@ -177,17 +178,22 @@ class ChatFoldersViewModel : ViewModel() {
     }
   }
 
-  fun updatePosition(fromIndex: Int, toIndex: Int) {
-    viewModelScope.launch(Dispatchers.IO) {
-      val folders = state.value.folders.toMutableList().apply { add(toIndex, removeAt(fromIndex)) }
-      val updatedFolders = folders.mapIndexed { index, chatFolderRecord ->
-        chatFolderRecord.copy(position = index)
-      }
-      ChatFoldersRepository.updatePositions(updatedFolders)
+  fun updateItemPosition(fromIndex: Int, toIndex: Int) {
+    val folders = state.value.folders.swap(fromIndex, toIndex)
+    val updatedFolders = folders.mapIndexed { index, chatFolderRecord ->
+      chatFolderRecord.copy(position = index)
+    }
+    internalState.update {
+      it.copy(folders = updatedFolders)
+    }
+  }
 
-      internalState.update {
-        it.copy(folders = updatedFolders)
-      }
+  fun saveItemPositions() {
+    val updatedFolders = state.value.folders.mapIndexed { index, chatFolderRecord ->
+      chatFolderRecord.copy(position = index)
+    }
+    viewModelScope.launch(Dispatchers.IO) {
+      ChatFoldersRepository.updatePositions(updatedFolders)
     }
   }