[FEATURE REQUEST] Maintain scroll position in file list

changelog/unreleased/4570

@@ -0,0 +1,6 @@
+Feature: Maintain scroll position when user scrolls and navigates in file/folder list
+
+Saves scroll position when user scrolls and navigates in file/folder list
+
+https://github.com/owncloud/android/issues/4528
+https://github.com/owncloud/android/pull/4570

owncloudApp/src/main/java/com/owncloud/android/presentation/files/filelist/MainFileListFragment.kt

@@ -798,10 +798,15 @@ class MainFileListFragment : Fragment(),
         collectLatestLifecycleFlow(mainFileListViewModel.fileListUiState) { fileListUiState ->
             if (fileListUiState !is MainFileListViewModel.FileListUiState.Success) return@collectLatestLifecycleFlow
 
+            saveScrollPosition()
+
             fileListAdapter.updateFileList(
                 filesToAdd = fileListUiState.folderContent,
                 fileListOption = fileListUiState.fileListOption,
             )
+
+            restoreScrollPosition()
+
             showOrHideEmptyView(fileListUiState)
 
             binding.spaceHeader.root.apply {
@@ -994,6 +999,38 @@ class MainFileListFragment : Fragment(),
         _binding = null
     }
 
+    /**
+     * Saves the current scroll position of the RecyclerView by capturing the indices of
+     * the last visible items from the StaggeredGridLayoutManager.
+     *
+     * This position is stored in the ViewModel so it can be restored later,
+     * typically after the adapter data is updated. This ensures continuity
+     * in the user’s scroll experience when navigating between fragments or refreshing data.
+     */
+    private fun saveScrollPosition() {
+        val layoutManager = binding.recyclerViewMainFileList.layoutManager as? StaggeredGridLayoutManager
+        mainFileListViewModel.lastVisibleItemPositions = layoutManager?.findLastVisibleItemPositions(null)
+    }
+
+    /**
+     * Restores the scroll position of the RecyclerView based on the previously
+     * saved positions in the ViewModel. It scrolls to the maximum of the last
+     * visible item positions captured earlier using [saveScrollPosition].
+     *
+     * This method is posted to the queue to ensure it runs after the
+     * RecyclerView has completed its layout pass and the adapter update has been applied.
+     */
+    private fun restoreScrollPosition() {
+        binding.recyclerViewMainFileList.post {
+            mainFileListViewModel.lastVisibleItemPositions?.let { positions ->
+                val maxPosition = positions.maxOrNull() ?: 0
+                binding.recyclerViewMainFileList.scrollToPosition(maxPosition)
+                mainFileListViewModel.lastVisibleItemPositions = null
+            }
+        }
+    }
+
+
     fun updateFileListOption(newFileListOption: FileListOption, file: OCFile) {
         mainFileListViewModel.updateFileListOption(newFileListOption)
         binding.swipeRefreshMainFileList.isEnabled = newFileListOption != FileListOption.AV_OFFLINE

owncloudApp/src/main/java/com/owncloud/android/presentation/files/filelist/MainFileListViewModel.kt

@@ -94,6 +94,7 @@ class MainFileListViewModel(
     fileListOptionParam: FileListOption,
 ) : ViewModel() {
 
+    var lastVisibleItemPositions: IntArray? = null
     private val showHiddenFiles: Boolean = sharedPreferencesProvider.getBoolean(PREF_SHOW_HIDDEN_FILES, false)
 
     val currentFolderDisplayed: MutableStateFlow<OCFile> = MutableStateFlow(initialFolderToDisplay)