enhance: select all button.

src/Shared/HandyControl_Shared/Controls/Attach/SelectAllButtonAttach.cs

@@ -0,0 +1,127 @@
+using System.Runtime.CompilerServices;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Controls.Primitives;
+
+namespace HandyControl.Controls;
+
+public class SelectAllButtonAttach
+{
+    private static readonly ConditionalWeakTable<Selector, ToggleButton> SelectorButtonTable = new();
+
+    public static readonly DependencyProperty TargetProperty = DependencyProperty.RegisterAttached(
+        "Target", typeof(Selector), typeof(SelectAllButtonAttach), new PropertyMetadata(null, OnTargetChanged));
+
+    public static void SetTarget(DependencyObject element, Selector value)
+        => element.SetValue(TargetProperty, value);
+
+    public static Selector GetTarget(DependencyObject element)
+        => (Selector) element.GetValue(TargetProperty);
+
+    private static void OnTargetChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
+    {
+        if (d is not ToggleButton button)
+        {
+            return;
+        }
+
+        button.Click -= OnButtonOnClick;
+
+        if (e.OldValue is Selector oldSelector)
+        {
+            oldSelector.SelectionChanged -= OnSelectorSelectionChanged;
+            SelectorButtonTable.Remove(oldSelector);
+        }
+
+        if (e.NewValue is not Selector newSelector)
+        {
+            return;
+        }
+
+        button.Click += OnButtonOnClick;
+        newSelector.SelectionChanged += OnSelectorSelectionChanged;
+
+        if (!SelectorButtonTable.TryGetValue(newSelector, out _))
+        {
+            SelectorButtonTable.Add(newSelector, button);
+        }
+    }
+
+    private static void OnButtonOnClick(object sender, RoutedEventArgs e)
+    {
+        if (sender is not ToggleButton button)
+        {
+            return;
+        }
+
+        if (button.IsChecked == true)
+        {
+            SelectAll(GetTarget(button));
+        }
+        else
+        {
+            UnselectAll(GetTarget(button));
+        }
+    }
+
+    private static void OnSelectorSelectionChanged(object sender, SelectionChangedEventArgs e)
+    {
+        if (sender is not Selector selector)
+        {
+            return;
+        }
+
+        if (!SelectorButtonTable.TryGetValue(selector, out var button))
+        {
+            return;
+        }
+
+        var selectedCount = GetSelectedItemsCount(selector);
+        var totalCount = selector.Items.Count;
+        button.IsChecked = selectedCount switch
+        {
+            0 => false,
+            _ when selectedCount == totalCount => true,
+            _ => null // Indeterminate
+        };
+    }
+
+    private static void SelectAll(Selector selector)
+    {
+        if (selector is MultiSelector multiSelector)
+        {
+            multiSelector.SelectAll();
+        }
+        else if (selector is ListBox listBox)
+        {
+            listBox.SelectAll();
+        }
+    }
+
+    private static void UnselectAll(Selector selector)
+    {
+        if (selector is MultiSelector multiSelector)
+        {
+            multiSelector.UnselectAll();
+        }
+        else if (selector is ListBox listBox)
+        {
+            listBox.UnselectAll();
+        }
+    }
+
+    private static int GetSelectedItemsCount(Selector selector)
+    {
+        if (selector is MultiSelector multiSelector)
+        {
+            return multiSelector.SelectedItems.Count;
+        }
+
+        if (selector is ListBox listBox)
+        {
+            return listBox.SelectedItems.Count;
+        }
+
+        return 0;
+    }
+}