Fix missing auto-scroll feature in RecyclerView when switching to multiselectview

Author: Scapesfear

AnkiDroid/src/main/java/com/ichi2/anki/CardBrowser.kt

@@ -153,6 +153,13 @@ open class CardBrowser :
      * When the list is changed, the position member of its elements should get changed. */
     private val cards get() = viewModel.cards
     private lateinit var deckSpinnerSelection: DeckSpinnerSelection
+    private var lastSelectedPosition
+        get() = viewModel.lastSelectedPosition
+        set(value) {
+            viewModel.lastSelectedPosition = value
+        }
+    private var oldCardTopOffset: Int = 0
+    private var oldCardId: Long? = null
 
     @VisibleForTesting
     lateinit var cardsListView: RecyclerView
@@ -349,11 +356,23 @@ open class CardBrowser :
 
     @VisibleForTesting
     fun onLongPress(id: CardOrNoteId) {
-        // click on whole cell triggers select
+        // Cell select triggers multi-select mode
         if (viewModel.isInMultiSelectMode && viewModel.lastSelectedId != null) {
+            // Select rows between the last selected ID and the current ID
             viewModel.selectRowsBetween(viewModel.lastSelectedId!!, id)
         } else {
-            viewModel.toggleRowSelection(id)
+            launchCatchingTask {
+                val position = getPositionForId(id)
+                // Save scrolling state to preserve UI consistency
+                lastSelectedPosition = position
+                saveScrollingState(position)
+
+                // Toggle selection of the card
+                viewModel.toggleRowSelection(id)
+
+                // Notify adapter about changes
+                cardsAdapter.notifyDataSetChanged()
+            }
         }
     }
 
@@ -484,6 +503,7 @@ open class CardBrowser :
                 // show title and hide spinner
                 actionBarTitle.visibility = View.VISIBLE
                 deckSpinnerSelection.setSpinnerVisibility(View.GONE)
+                autoScrollTo(lastSelectedPosition)
             } else {
                 Timber.d("end multiselect mode")
                 // update adapter to remove check boxes
@@ -1909,6 +1929,35 @@ open class CardBrowser :
             viewModel: CardBrowserViewModel,
         ): Intent = NoteEditorLauncher.AddNoteFromCardBrowser(viewModel).getIntent(context)
     }
+
+    private suspend fun saveScrollingState(position: Int) {
+        // Save the current card id and its top offset
+        oldCardId = viewModel.queryCardIdAtPosition(position)
+        oldCardTopOffset = calculateTopOffset(position)
+    }
+
+    private fun calculateTopOffset(cardPosition: Int): Int {
+        // Calculate the top offset of the card at the given position
+        val layoutManager = cardsListView.layoutManager as? LinearLayoutManager ?: return 0
+        val firstVisiblePosition = layoutManager.findFirstVisibleItemPosition()
+        val view = cardsListView.getChildAt(cardPosition - firstVisiblePosition)
+        return view?.top ?: 0
+    }
+
+    private fun autoScrollTo(newPosition: Int) {
+        (cardsListView.layoutManager as? LinearLayoutManager)?.scrollToPositionWithOffset(newPosition, oldCardTopOffset)
+    }
+
+    fun getPositionForId(id: CardOrNoteId): Int {
+        // Search through rowCollection for the CardOrNoteId and return its position
+        val rowCollection = cardsAdapter.rowCollection
+        for (position in 0 until rowCollection.size) {
+            if (rowCollection[position] == id) {
+                return position
+            }
+        }
+        return RecyclerView.NO_POSITION
+    }
 }
 
 suspend fun searchForRows(

AnkiDroid/src/main/java/com/ichi2/anki/browser/BrowserMultiColumnAdapter.kt

@@ -63,7 +63,7 @@ class BrowserMultiColumnAdapter(
     val fontSizeScalePercent =
         sharedPrefs().getInt("relativeCardBrowserFontSize", DEFAULT_FONT_SIZE_RATIO)
 
-    private val rowCollection: BrowserRowCollection
+    val rowCollection: BrowserRowCollection
         get() = viewModel.cards
 
     private var originalTextSize = -1.0f

AnkiDroid/src/main/java/com/ichi2/anki/browser/CardBrowserViewModel.kt

@@ -181,7 +181,7 @@ class CardBrowserViewModel(
     internal suspend fun queryAllCardIds() = cards.queryCardIds()
 
     var lastSelectedId: CardOrNoteId? = null
-
+    var lastSelectedPosition = 0
     val flowOfIsInMultiSelectMode =
         flowOfSelectedRows
             .map { it.isNotEmpty() }