fix(card-browser): end multiselect position

If ending multiselect using navigation it felt best to 'anchor'
 the list on the first visible selected row (so it stays in the same
 position)

If there is no selected item in view, the item at the top of the list
 is maintained

Author: david-allison

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

@@ -52,6 +52,7 @@ import com.ichi2.anki.launchCatchingTask
 import com.ichi2.anki.observability.ChangeManager
 import com.ichi2.anki.snackbar.showSnackbar
 import com.ichi2.anki.ui.attachFastScroller
+import com.ichi2.anki.utils.ext.visibleItemPositions
 import com.ichi2.utils.HandlerUtils
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.launch
@@ -72,6 +73,10 @@ class CardBrowserFragment :
     @VisibleForTesting
     lateinit var cardsListView: RecyclerView
 
+    /** LayoutManager for [cardsListView] */
+    val layoutManager: LinearLayoutManager
+        get() = cardsListView.layoutManager as LinearLayoutManager
+
     @VisibleForTesting
     lateinit var browserColumnHeadings: ViewGroup
 
@@ -144,9 +149,26 @@ class CardBrowserFragment :
             // update adapter to remove check boxes
             cardsAdapter.notifyDataSetChanged()
             if (modeChange is SingleSelectCause.DeselectRow) {
+                cardsAdapter.notifyDataSetChanged()
                 autoScrollTo(modeChange.selection)
             } else if (modeChange is MultiSelectCause.RowSelected) {
+                cardsAdapter.notifyDataSetChanged()
                 autoScrollTo(modeChange.selection)
+            } else if (modeChange is SingleSelectCause && !modeChange.previouslySelectedRowIds.isNullOrEmpty()) {
+                // if any visible rows are selected, anchor on the first row
+
+                // obtain the offset of the row before we call notifyDataSetChanged
+                val rowPositionAndOffset =
+                    try {
+                        val visibleRowIds = layoutManager.visibleItemPositions.map { viewModel.getRowAtPosition(it) }
+                        val firstVisibleRowId = visibleRowIds.firstOrNull { modeChange.previouslySelectedRowIds!!.contains(it) }
+                        firstVisibleRowId?.let { firstVisibleRowId.toRowSelection() }
+                    } catch (e: Exception) {
+                        Timber.w(e)
+                        null
+                    }
+                cardsAdapter.notifyDataSetChanged()
+                rowPositionAndOffset?.let { autoScrollTo(it) }
             }
         }
 
@@ -276,15 +298,14 @@ class CardBrowserFragment :
         }
 
     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(rowSelection: RowSelection) {
         val newPosition = viewModel.getPositionOfId(rowSelection.rowId) ?: return
-        (cardsListView.layoutManager as LinearLayoutManager).scrollToPositionWithOffset(newPosition, rowSelection.topOffset)
+        layoutManager.scrollToPositionWithOffset(newPosition, rowSelection.topOffset)
     }
 
     private fun CardOrNoteId.toRowSelection() =

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

@@ -598,8 +598,12 @@ class CardBrowserViewModel(
     fun selectNone(): Job? {
         if (_selectedRows.isEmpty()) return null
         Timber.d("selecting none")
+        val removalReason =
+            SingleSelectCause.Other.apply {
+                this.previouslySelectedRowIds = _selectedRows.toSet()
+            }
         _selectedRows.clear()
-        return onRemoveSelectedRows(disableMultiSelectIfEmpty = false, reason = SingleSelectCause.Other)
+        return onRemoveSelectedRows(disableMultiSelectIfEmpty = false, reason = removalReason)
     }
 
     /**
@@ -1075,6 +1079,7 @@ class CardBrowserViewModel(
      * Turn off [Multi-Select Mode][isInMultiSelectMode] and return to normal state
      */
     fun endMultiSelectMode(reason: SingleSelectCause) {
+        reason.previouslySelectedRowIds = _selectedRows.toSet()
         _selectedRows.clear()
         flowOfMultiSelectModeChanged.value = reason
     }
@@ -1286,6 +1291,8 @@ class CardBrowserViewModel(
             data object NavigateBack : SingleSelectCause()
 
             data object Other : SingleSelectCause()
+
+            var previouslySelectedRowIds: Set<CardOrNoteId>? = null
         }
 
         sealed class MultiSelectCause : ChangeMultiSelectMode() {

AnkiDroid/src/main/java/com/ichi2/anki/utils/ext/LinearLayoutManager.kt

@@ -0,0 +1,37 @@
+/*
+ *  Copyright (c) 2025 David Allison <davidallisongithub@gmail.com>
+ *
+ *  This program is free software; you can redistribute it and/or modify it under
+ *  the terms of the GNU General Public License as published by the Free Software
+ *  Foundation; either version 3 of the License, or (at your option) any later
+ *  version.
+ *
+ *  This program is distributed in the hope that it will be useful, but WITHOUT ANY
+ *  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ *  PARTICULAR PURPOSE. See the GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along with
+ *  this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.ichi2.anki.utils.ext
+
+import androidx.recyclerview.widget.LinearLayoutManager
+import androidx.recyclerview.widget.RecyclerView
+
+/**
+ * Returns range of adapter positions of the visible items.
+ *
+ * This position does not include adapter changes that were dispatched after the last layout pass.
+ *
+ * Returns [IntRange.EMPTY] if the [LinearLayoutManager] contains no items.
+ */
+val LinearLayoutManager.visibleItemPositions: IntRange
+    get() {
+        val first = findFirstVisibleItemPosition()
+        val last = findLastVisibleItemPosition()
+        if (first == RecyclerView.NO_POSITION || last == RecyclerView.NO_POSITION) {
+            return IntRange.EMPTY
+        }
+        return first..last
+    }