Add Auto-Scroll Support for RecyclerView in Multiselect View

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

@@ -345,6 +345,8 @@ open class CardBrowser :
         launchCatchingTask {
             if (viewModel.isInMultiSelectMode) {
                 viewModel.toggleRowSelection(id)
+                viewModel.saveScrollingState(id)
+                viewModel.oldCardTopOffset = calculateTopOffset(viewModel.lastSelectedPosition)
             } else {
                 val cardId = viewModel.queryDataForCardEdit(id)
                 openNoteEditorForCard(cardId)
@@ -357,6 +359,8 @@ open class CardBrowser :
         if (viewModel.isInMultiSelectMode && viewModel.lastSelectedId != null) {
             viewModel.selectRowsBetween(viewModel.lastSelectedId!!, id)
         } else {
+            viewModel.saveScrollingState(id)
+            viewModel.oldCardTopOffset = calculateTopOffset(viewModel.lastSelectedPosition)
             viewModel.toggleRowSelection(id)
         }
     }
@@ -509,6 +513,7 @@ open class CardBrowser :
                 // Due to the ripple on long press, we set padding
                 browserColumnHeadings.updatePaddingRelative(start = 48.dp)
                 multiSelectOnBackPressedCallback.isEnabled = true
+                autoScrollTo(viewModel.lastSelectedPosition, viewModel.oldCardTopOffset)
             } else {
                 Timber.d("end multiselect mode")
                 // update adapter to remove check boxes
@@ -517,6 +522,7 @@ open class CardBrowser :
                 actionBarTitle.visibility = View.GONE
                 browserColumnHeadings.updatePaddingRelative(start = 0.dp)
                 multiSelectOnBackPressedCallback.isEnabled = false
+                autoScrollTo(viewModel.lastSelectedPosition, viewModel.oldCardTopOffset)
             }
             // reload the actionbar using the multi-select mode actionbar
             invalidateOptionsMenu()
@@ -1865,6 +1871,20 @@ open class CardBrowser :
             viewModel: CardBrowserViewModel,
         ): Intent = NoteEditorLauncher.AddNoteFromCardBrowser(viewModel).getIntent(context)
     }
+
+    private fun calculateTopOffset(cardPosition: Int): Int {
+        val layoutManager = cardsListView.layoutManager as LinearLayoutManager
+        val firstVisiblePosition = layoutManager.findFirstVisibleItemPosition()
+        val view = cardsListView.getChildAt(cardPosition - firstVisiblePosition)
+        return view?.top ?: 0
+    }
+
+    private fun autoScrollTo(
+        newPosition: Int,
+        offset: Int,
+    ) {
+        (cardsListView.layoutManager as LinearLayoutManager).scrollToPositionWithOffset(newPosition, offset)
+    }
 }
 
 suspend fun searchForRows(

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

@@ -101,6 +101,9 @@ class CardBrowserViewModel(
     private val manualInit: Boolean = false,
 ) : ViewModel(),
     SharedPreferencesProvider by preferences {
+    var lastSelectedPosition: Int = 0
+    var oldCardTopOffset: Int = 0
+
     // TODO: abstract so we can use a `Context` and `pref_display_filenames_in_browser_key`
     val showMediaFilenames = sharedPrefs().getBoolean("card_browser_show_media_filenames", false)
 
@@ -1030,6 +1033,12 @@ class CardBrowserViewModel(
             val error: String,
         ) : SearchState
     }
+
+    fun saveScrollingState(id: CardOrNoteId) {
+        cards.indexOf(id).takeIf { it >= 0 }?.let { position ->
+            lastSelectedPosition = position
+        }
+    }
 }
 
 enum class SaveSearchResult {

AnkiDroid/src/test/java/com/ichi2/anki/CardBrowserTest.kt

@@ -936,6 +936,23 @@ class CardBrowserTest : RobolectricTest() {
             assertThat(cardBrowser.viewModel.rowCount, equalTo(3))
         }
 
+    @Test
+    fun checkIfScrollPositionSavedOnLongPress() =
+        runTest {
+            val cardBrowser = getBrowserWithNotes(10)
+            cardBrowser.longClickRowAtPosition(5)
+            assertThat(cardBrowser.viewModel.lastSelectedPosition, equalTo(5))
+        }
+
+    @Test
+    fun checkIfScrollPositionSavedOnTap() =
+        runTest {
+            val cardBrowser = getBrowserWithNotes(10)
+            cardBrowser.longClickRowAtPosition(1)
+            cardBrowser.clickRowAtPosition(5)
+            assertThat(cardBrowser.viewModel.lastSelectedPosition, equalTo(5))
+        }
+
     @Test
     fun `column spinner positions are set if no preferences exist`() =
         runBlocking {