feat: implement MultiAutoCompleteSelectionAdapter for enhanced selection handling

src/Ursa/Controls/AutoCompleteBox/MultiAutoCompleteBox.cs

@@ -539,7 +539,7 @@ public partial class MultiAutoCompleteBox : TemplatedControl, IInnerContentContr
             adapter = selector as ISelectionAdapter;
             if (adapter == null)
                 // Built in support for wrapping a Selector control
-                adapter = new SelectingItemsControlSelectionAdapter(selector);
+                adapter = new MultiAutoCompleteSelectionAdapter(selector);
         }
 
         if (adapter == null) adapter = nameScope.Find<ISelectionAdapter>(ElementSelectionAdapter);

src/Ursa/Controls/AutoCompleteBox/MultiAutoCompleteSelectionAdapter.cs

@@ -0,0 +1,298 @@
+using System.Collections;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
+using Avalonia.Controls.Utils;
+using Avalonia.Input;
+using Avalonia.Interactivity;
+using Avalonia.LogicalTree;
+
+namespace Ursa.Controls;
+
+public class MultiAutoCompleteSelectionAdapter : ISelectionAdapter
+{
+    /// <summary>
+    ///     The SelectingItemsControl instance.
+    /// </summary>
+    private SelectingItemsControl? _selector;
+
+    private object? _previewSelectedItem;
+    private object? _selectedItem;
+
+    /// <summary>
+    ///     Initializes a new instance of the
+    ///     <see cref="T:Avalonia.Controls.Utils.SelectingItemsControlSelectionAdapter" />
+    ///     class.
+    /// </summary>
+    public MultiAutoCompleteSelectionAdapter()
+    {
+    }
+
+    /// <summary>
+    ///     Initializes a new instance of the
+    ///     <see cref="T:Avalonia.Controls.Utils.SelectingItemsControlSelectionAdapterr" />
+    ///     class with the specified
+    ///     <see cref="T:Avalonia.Controls.Primitives.SelectingItemsControl" />
+    ///     control.
+    /// </summary>
+    /// <param name="selector">
+    ///     The
+    ///     <see cref="T:Avalonia.Controls.Primitives.SelectingItemsControl" /> control
+    ///     to wrap as a
+    ///     <see cref="T:Avalonia.Controls.Utils.SelectingItemsControlSelectionAdapter" />.
+    /// </param>
+    public MultiAutoCompleteSelectionAdapter(SelectingItemsControl selector)
+    {
+        SelectorControl = selector;
+    }
+
+
+    /// <summary>
+    ///     Gets or sets a value indicating whether the selection change event
+    ///     should not be fired.
+    /// </summary>
+    private bool IgnoringSelectionChanged { get; set; }
+
+    /// <summary>
+    ///     Gets or sets the underlying
+    ///     <see cref="T:Avalonia.Controls.Primitives.SelectingItemsControl" />
+    ///     control.
+    /// </summary>
+    /// <value>
+    ///     The underlying
+    ///     <see cref="T:Avalonia.Controls.Primitives.SelectingItemsControl" />
+    ///     control.
+    /// </value>
+    public SelectingItemsControl? SelectorControl
+    {
+        get => _selector;
+
+        set
+        {
+            if (_selector != null)
+            {
+                _selector.SelectionChanged -= OnSelectionChanged;
+                _selector.PointerReleased -= OnSelectorPointerReleased;
+            }
+
+            _selector = value;
+
+            if (_selector != null)
+            {
+                _selector.SelectionChanged += OnSelectionChanged;
+                _selector.PointerReleased += OnSelectorPointerReleased;
+            }
+        }
+    }
+
+    /// <summary>
+    ///     Occurs when the
+    ///     <see cref="P:Avalonia.Controls.Utils.SelectingItemsControlSelectionAdapter.SelectedItem" />
+    ///     property value changes.
+    /// </summary>
+    public event EventHandler<SelectionChangedEventArgs>? SelectionChanged;
+
+    /// <summary>
+    ///     Occurs when an item is selected and is committed to the underlying
+    ///     <see cref="T:Avalonia.Controls.Primitives.SelectingItemsControl" />
+    ///     control.
+    /// </summary>
+    public event EventHandler<RoutedEventArgs>? Commit;
+
+    /// <summary>
+    ///     Occurs when a selection is canceled before it is committed.
+    /// </summary>
+    public event EventHandler<RoutedEventArgs>? Cancel;
+
+    /// <summary>
+    ///     Gets or sets the selected item of the selection adapter.
+    /// </summary>
+    /// <value>The selected item of the underlying selection adapter.</value>
+    public object? SelectedItem
+    {
+        get => _selectedItem;
+
+        set
+        {
+            IgnoringSelectionChanged = true;
+            if (SelectorControl != null)
+            {
+                _selectedItem = value;
+                SelectorControl.SelectedItem = value;
+            }
+            // Attempt to reset the scroll viewer's position
+            if (value == null) ResetScrollViewer();
+            IgnoringSelectionChanged = false;
+        }
+    }
+
+    /// <summary>
+    ///     Gets or sets a collection that is used to generate the content of
+    ///     the selection adapter.
+    /// </summary>
+    /// <value>
+    ///     The collection used to generate content for the selection
+    ///     adapter.
+    /// </value>
+    public IEnumerable? ItemsSource
+    {
+        get => SelectorControl?.ItemsSource;
+        set
+        {
+            if (SelectorControl != null) SelectorControl.ItemsSource = value;
+        }
+    }
+
+    /// <summary>
+    ///     Provides handling for the
+    ///     <see cref="E:Avalonia.Input.InputElement.KeyDown" /> event that occurs
+    ///     when a key is pressed while the drop-down portion of the
+    ///     <see cref="T:Avalonia.Controls.AutoCompleteBox" /> has focus.
+    /// </summary>
+    /// <param name="e">
+    ///     A <see cref="T:Avalonia.Input.KeyEventArgs" />
+    ///     that contains data about the
+    ///     <see cref="E:Avalonia.Input.InputElement.KeyDown" /> event.
+    /// </param>
+    public void HandleKeyDown(KeyEventArgs e)
+    {
+        switch (e.Key)
+        {
+            case Key.Enter:
+                OnCommit();
+                e.Handled = true;
+                break;
+
+            case Key.Up:
+                SelectedIndexDecrement();
+                e.Handled = true;
+                break;
+
+            case Key.Down:
+                if ((e.KeyModifiers & KeyModifiers.Alt) == KeyModifiers.None)
+                {
+                    SelectedIndexIncrement();
+                    e.Handled = true;
+                }
+
+                break;
+
+            case Key.Escape:
+                OnCancel();
+                e.Handled = true;
+                break;
+        }
+    }
+
+    /// <summary>
+    ///     If the control contains a ScrollViewer, this will reset the viewer
+    ///     to be scrolled to the top.
+    /// </summary>
+    private void ResetScrollViewer()
+    {
+        if (SelectorControl != null)
+        {
+            var sv = SelectorControl.GetLogicalDescendants().OfType<ScrollViewer>().FirstOrDefault();
+            if (sv != null) sv.Offset = new Vector(0, 0);
+        }
+    }
+
+    /// <summary>
+    ///     Handles the mouse left button up event on the selector control.
+    /// </summary>
+    /// <param name="sender">The source object.</param>
+    /// <param name="e">The event data.</param>
+    private void OnSelectorPointerReleased(object? sender, PointerReleasedEventArgs e)
+    {
+        if (e.InitialPressMouseButton == MouseButton.Left) OnCommit();
+    }
+
+    /// <summary>
+    ///     Handles the SelectionChanged event on the SelectingItemsControl control.
+    /// </summary>
+    /// <param name="sender">The source object.</param>
+    /// <param name="e">The selection changed event data.</param>
+    private void OnSelectionChanged(object? sender, SelectionChangedEventArgs e)
+    {
+        if (IgnoringSelectionChanged) return;
+        _previewSelectedItem = SelectorControl?.SelectedItem;
+    }
+
+    /// <summary>
+    ///     Increments the
+    ///     <see cref="P:Avalonia.Controls.Primitives.SelectingItemsControl.SelectedIndex" />
+    ///     property of the underlying
+    ///     <see cref="T:Avalonia.Controls.Primitives.SelectingItemsControl" />
+    ///     control.
+    /// </summary>
+    protected void SelectedIndexIncrement()
+    {
+        if (SelectorControl != null)
+            SelectorControl.SelectedIndex = SelectorControl.SelectedIndex + 1 >= SelectorControl.ItemCount
+                ? -1
+                : SelectorControl.SelectedIndex + 1;
+    }
+
+    /// <summary>
+    ///     Decrements the
+    ///     <see cref="P:Avalonia.Controls.Primitives.SelectingItemsControl.SelectedIndex" />
+    ///     property of the underlying
+    ///     <see cref="T:Avalonia.Controls.Primitives.SelectingItemsControl" />
+    ///     control.
+    /// </summary>
+    protected void SelectedIndexDecrement()
+    {
+        if (SelectorControl != null)
+        {
+            var index = SelectorControl.SelectedIndex;
+            if (index >= 0)
+                SelectorControl.SelectedIndex--;
+            else if (index == -1) SelectorControl.SelectedIndex = SelectorControl.ItemCount - 1;
+        }
+    }
+
+    /// <summary>
+    ///     Raises the
+    ///     <see cref="E:Avalonia.Controls.Utils.SelectingItemsControlSelectionAdapter.Commit" />
+    ///     event.
+    /// </summary>
+    internal void OnCommit()
+    {
+        SelectedItem = _previewSelectedItem;
+        SelectionChanged?.Invoke(this,
+            new SelectionChangedEventArgs(
+                SelectingItemsControl.SelectionChangedEvent,
+                new List<object?>(),
+                new List<object?> { SelectedItem }
+            )
+        );
+        Commit?.Invoke(this, new RoutedEventArgs());
+        AfterAdapterAction();
+    }
+
+    /// <summary>
+    ///     Raises the
+    ///     <see cref="E:Avalonia.Controls.Utils.SelectingItemsControlSelectionAdapter.Cancel" />
+    ///     event.
+    /// </summary>
+    private void OnCancel()
+    {
+        Cancel?.Invoke(this, new RoutedEventArgs());
+        AfterAdapterAction();
+    }
+    
+    /// <summary>
+    ///     Change the selection after the actions are complete.
+    /// </summary>
+    private void AfterAdapterAction()
+    {
+        IgnoringSelectionChanged = true;
+        if (SelectorControl != null)
+        {
+            SelectorControl.SelectedItem = null;
+            SelectorControl.SelectedIndex = -1;
+            _previewSelectedItem = null;
+        }
+        IgnoringSelectionChanged = false;
+    }
+}