Sync TableView SelectedItems with the always-selected row 0 (#13230)

src/ui/Logic/TableViewExtras.cs

@@ -273,6 +273,18 @@ public static TableView MakeTableView(bool alwaysSelected = true, bool multiSele
 
         UiUtil.ApplyTableViewRowStyle(tableView);
 
+        // SelectionMode.AlwaysSelected picks row 0 the moment ItemsSource is assigned, but that
+        // pick only reaches the internal selection model (and SelectedItem/SelectedIndex) - the
+        // SelectedItems collection stays empty and no SelectionChanged is raised. Repair it
+        // (#13230), see SyncSelectedItemsWithSelection.
+        tableView.PropertyChanged += (_, e) =>
+        {
+            if (e.Property == ItemsControl.ItemsSourceProperty)
+            {
+                SyncSelectedItemsWithSelection(tableView);
+            }
+        };
+
         // Home/End/PageUp/PageDown (and Ctrl+Home/End) list navigation in every grid (#13194).
         // Handlers attached earlier in the routing path (window-level tunnel handlers, shortcut
         // dispatch) still win; this is the fallback when nothing else handled the key.
@@ -281,6 +293,44 @@ public static TableView MakeTableView(bool alwaysSelected = true, bool multiSele
         return tableView;
     }
 
+    /// <summary>
+    /// Puts the rows the control considers selected into its <see cref="SelectingItemsControl.SelectedItems"/>
+    /// collection when that collection is empty but the selection model is not.
+    /// <para>
+    /// <see cref="SelectionMode.AlwaysSelected"/> selects row 0 as soon as ItemsSource is assigned
+    /// to a populated collection. That selection reaches the selection model - the row is drawn
+    /// highlighted and SelectedItem/SelectedIndex point at it - but SelectedItems is left empty and
+    /// no SelectionChanged is raised, and neither a layout pass nor a Selection.Clear()/Select(0)
+    /// repairs it; only moving the selection to a different row does. Everything in Subtitle Edit
+    /// reads the selection through SelectedItems, so the grid showed row 1 highlighted while the
+    /// app saw nothing selected: the edit box, Show and Duration went blank the moment anything
+    /// re-read the selection, and a shift-selection starting at row 1 silently left row 1 out of
+    /// every operation (issue #13230).
+    /// </para>
+    /// </summary>
+    public static void SyncSelectedItemsWithSelection(TableView tableView)
+    {
+        var selectedItems = tableView.SelectedItems;
+        if (selectedItems == null || selectedItems.Count > 0)
+        {
+            return;
+        }
+
+        var selection = tableView.Selection;
+        if (selection.Count == 0)
+        {
+            return;
+        }
+
+        foreach (var item in selection.SelectedItems)
+        {
+            if (item != null)
+            {
+                selectedItems.Add(item);
+            }
+        }
+    }
+
     /// <summary>
     /// A read-only text cell whose flow direction follows its own content, the way the
     /// main subtitle grid's text cells do. Use it for every column showing subtitle text

tests/UI/Logic/TableViewSelectionSyncTests.cs

@@ -0,0 +1,146 @@
+using Avalonia.Controls;
+using Avalonia.Data;
+using Avalonia.Headless.XUnit;
+using Nikse.SubtitleEdit.Logic;
+using System.Collections.ObjectModel;
+using System.ComponentModel;
+
+namespace UITests.Logic;
+
+/// <summary>
+/// SelectionMode.AlwaysSelected picks row 0 when ItemsSource is assigned without ever filling the
+/// control's SelectedItems collection. Subtitle Edit reads every selection through SelectedItems,
+/// so the grid showed the first row highlighted while the app saw nothing selected - the edit box
+/// and time codes went blank and a selection starting at row 1 left row 1 out (issue #13230).
+/// <see cref="TableViewExtras.MakeTableView"/> repairs the collection on every ItemsSource change.
+/// </summary>
+public class TableViewSelectionSyncTests
+{
+    private sealed class Row
+    {
+        public string Text { get; set; } = string.Empty;
+    }
+
+    private sealed class Vm : INotifyPropertyChanged
+    {
+        private object? _selected;
+        private int? _selectedIndex;
+
+        public object? Selected
+        {
+            get => _selected;
+            set
+            {
+                _selected = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Selected)));
+            }
+        }
+
+        public int? SelectedIndex
+        {
+            get => _selectedIndex;
+            set
+            {
+                _selectedIndex = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(SelectedIndex)));
+            }
+        }
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+    }
+
+    /// <summary>
+    /// The main subtitle grid: multi-select, always selected, with the view model's current row and
+    /// index bound two-way - and filled the way SetSubtitles fills it (detach, fill, re-attach).
+    /// </summary>
+    private static (TableView Grid, Vm Vm, ObservableCollection<Row> Items) MakeGridWithRows(int rowCount)
+    {
+        var items = new ObservableCollection<Row>();
+        var vm = new Vm();
+
+        var grid = TableViewExtras.MakeTableView();
+        grid.Columns.Add(new TableViewColumn { Header = "Text", Binding = new Binding(nameof(Row.Text)) });
+        grid.ItemsSource = items;
+        grid[!TableView.SelectedItemProperty] = new Binding(nameof(vm.Selected)) { Mode = BindingMode.TwoWay, Source = vm };
+        grid[!TableView.SelectedIndexProperty] = new Binding(nameof(vm.SelectedIndex)) { Mode = BindingMode.TwoWay, Source = vm };
+
+        new Window { Width = 400, Height = 300, Content = grid }.Show();
+
+        grid.ItemsSource = null;
+        for (var i = 1; i <= rowCount; i++)
+        {
+            items.Add(new Row { Text = "line " + i });
+        }
+
+        grid.ItemsSource = items;
+
+        return (grid, vm, items);
+    }
+
+    [AvaloniaFact]
+    public void FirstRowIsInSelectedItemsAfterFillingTheGrid()
+    {
+        var (grid, vm, items) = MakeGridWithRows(20);
+
+        Assert.Same(items[0], grid.SelectedItem);
+        Assert.Same(items[0], vm.Selected);
+        Assert.Equal(1, grid.Selection.Count);
+
+        // Without the repair this is empty: the row is highlighted but nothing is selected as far
+        // as the rest of the application can tell.
+        Assert.Single(grid.SelectedItems!);
+        Assert.Same(items[0], grid.SelectedItems![0]);
+    }
+
+    [AvaloniaFact]
+    public void SelectingARangeFromTheFirstRowKeepsTheFirstRow()
+    {
+        var (grid, _, items) = MakeGridWithRows(20);
+
+        // How the main grid applies a shift-selection (SelectGridRange).
+        grid.Selection.BeginBatchUpdate();
+        grid.Selection.Clear();
+        grid.Selection.Select(4);
+        grid.Selection.SelectRange(0, 4);
+        grid.Selection.EndBatchUpdate();
+
+        Assert.Equal(5, grid.Selection.Count);
+
+        // Without the repair row 0 is missing here, so italic/copy/delete skipped the first line.
+        var selected = grid.SelectedItems!.Cast<Row>().Select(r => r.Text).Order().ToArray();
+        Assert.Equal(new[] { "line 1", "line 2", "line 3", "line 4", "line 5" }, selected);
+        Assert.Contains(items[0], grid.SelectedItems!.Cast<Row>());
+    }
+
+    [AvaloniaFact]
+    public void EmptyGridSelectsNothing()
+    {
+        var (grid, vm, _) = MakeGridWithRows(0);
+
+        Assert.Equal(0, grid.Selection.Count);
+        Assert.Empty(grid.SelectedItems!);
+        Assert.Null(grid.SelectedItem);
+        Assert.Null(vm.Selected);
+    }
+
+    [AvaloniaFact]
+    public void RefillingTheGridKeepsSelectedItemsInSync()
+    {
+        var (grid, vm, _) = MakeGridWithRows(20);
+
+        // A later reload (format change, undo, import, ...) goes through the same detach/fill/attach.
+        var newItems = new ObservableCollection<Row>();
+        for (var i = 1; i <= 5; i++)
+        {
+            newItems.Add(new Row { Text = "new " + i });
+        }
+
+        grid.ItemsSource = null;
+        grid.ItemsSource = newItems;
+
+        Assert.Same(newItems[0], grid.SelectedItem);
+        Assert.Same(newItems[0], vm.Selected);
+        Assert.Single(grid.SelectedItems!);
+        Assert.Same(newItems[0], grid.SelectedItems![0]);
+    }
+}