Add SelectingItemsControlSearchBehavior behavior

samples/BehaviorsTestApplication/Controls/SingleSelectionTabControl.cs

@@ -0,0 +1,14 @@
+using System;
+using Avalonia.Controls;
+
+namespace BehaviorsTestApplication.Controls;
+
+public class SingleSelectionTabControl : TabControl
+{
+    protected override Type StyleKeyOverride => typeof(TabControl);
+
+    static SingleSelectionTabControl()
+    {
+        SelectionModeProperty.OverrideDefaultValue<SingleSelectionTabControl>(SelectionMode.Single);
+    }
+}

samples/BehaviorsTestApplication/Views/MainView.axaml

@@ -13,17 +13,20 @@
     </Style>
   </UserControl.Styles>
   <DockPanel>
-    <TextBox x:Name="SearchBox" 
-             Watermark="Search pages..." 
-             Margin="0,0,0,8" 
-             TextChanged="OnSearchTextChanged"
+    <TextBox x:Name="SearchBox"
+             Watermark="Search pages..."
+             Margin="0,0,0,8"
              DockPanel.Dock="Top"  />
     <TextBlock x:Name="NoMatchesText" 
                Text="No pages match the search." 
                Margin="0,0,0,8" 
                IsVisible="False"
                DockPanel.Dock="Top" />
-    <TabControl x:Name="PagesTabControl" Classes="sidebar">
+    <SingleSelectionTabControl x:Name="PagesTabControl" SelectedIndex="0" Classes="sidebar">
+      <Interaction.Behaviors>
+        <SelectingItemsControlSearchBehavior SearchBox="SearchBox"
+                                             NoMatchesControl="NoMatchesText" />
+      </Interaction.Behaviors>
       <TabItem Header="CallMethodAction">
         <pages:CallMethodActionView />
       </TabItem>
@@ -150,6 +153,6 @@
       <TabItem Header="Reactive Navigation">
         <pages:ReactiveNavigationView />
       </TabItem>
-    </TabControl>
+    </SingleSelectionTabControl>
   </DockPanel>
 </UserControl>

samples/BehaviorsTestApplication/Views/MainView.axaml.cs

@@ -1,5 +1,4 @@
-using Avalonia.Controls;
-using System.Linq;
+using Avalonia.Controls;
 
 namespace BehaviorsTestApplication.Views;
 
@@ -9,28 +8,4 @@ public MainView()
     {
         InitializeComponent();
     }
-
-    private void OnSearchTextChanged(object? sender, Avalonia.Interactivity.RoutedEventArgs e)
-    {
-        var query = SearchBox.Text?.ToLowerInvariant() ?? string.Empty;
-        var visibleCount = 0;
-
-        var tabItems = PagesTabControl.Items.OfType<TabItem>().ToList();
-
-        foreach (var item in tabItems)
-        {
-            var header = item.Header?.ToString()?.ToLowerInvariant() ?? string.Empty;
-            var visible = header.Contains(query);
-            item.IsVisible = visible;
-
-            if (visible)
-            {
-                visibleCount++;
-            }
-        }
-
-        PagesTabControl.SelectedItem = tabItems.FirstOrDefault(x => x.IsVisible);
-
-        NoMatchesText.IsVisible = visibleCount == 0;
-    }
 }

src/Avalonia.Xaml.Interactions.Custom/SelectingItemsControl/SelectingItemsControlSearchBehavior.cs

@@ -0,0 +1,96 @@
+using System.Linq;
+using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
+using Avalonia.Input;
+using Avalonia.Interactivity;
+using Avalonia.Xaml.Interactivity;
+
+namespace Avalonia.Xaml.Interactions.Custom;
+
+/// <summary>
+/// Filters <see cref="SelectingItemsControl"/> items based on the text of a search box.
+/// </summary>
+public sealed class SelectingItemsControlSearchBehavior : StyledElementBehavior<SelectingItemsControl>
+{
+    /// <summary>
+    /// Identifies the <seealso cref="SearchBox"/> avalonia property.
+    /// </summary>
+    public static readonly StyledProperty<TextBox?> SearchBoxProperty =
+        AvaloniaProperty.Register<SelectingItemsControlSearchBehavior, TextBox?>(nameof(SearchBox));
+
+    /// <summary>
+    /// Identifies the <seealso cref="NoMatchesControl"/> avalonia property.
+    /// </summary>
+    public static readonly StyledProperty<TextBlock?> NoMatchesControlProperty =
+        AvaloniaProperty.Register<SelectingItemsControlSearchBehavior, TextBlock?>(nameof(NoMatchesControl));
+
+    /// <summary>
+    /// Gets or sets the search box control.
+    /// </summary>
+    [ResolveByName]
+    public TextBox? SearchBox
+    {
+        get => GetValue(SearchBoxProperty);
+        set => SetValue(SearchBoxProperty, value);
+    }
+
+    /// <summary>
+    /// Gets or sets the control displayed when no matches are found.
+    /// </summary>
+    [ResolveByName]
+    public Control? NoMatchesControl
+    {
+        get => GetValue(NoMatchesControlProperty);
+        set => SetValue(NoMatchesControlProperty, value);
+    }
+
+    /// <inheritdoc />
+    protected override void OnAttachedToVisualTree()
+    {
+        if (SearchBox is not null)
+        {
+            SearchBox.AddHandler(InputElement.TextInputEvent, SearchBox_TextChanged, RoutingStrategies.Bubble);
+            SearchBox.AddHandler(TextBox.TextChangedEvent, SearchBox_TextChanged, RoutingStrategies.Bubble);
+        }
+    }
+
+    /// <inheritdoc />
+    protected override void OnDetachedFromVisualTree()
+    {
+        if (SearchBox is not null)
+        {
+            SearchBox.RemoveHandler(InputElement.TextInputEvent, SearchBox_TextChanged);
+            SearchBox.RemoveHandler(TextBox.TextChangedEvent, SearchBox_TextChanged);
+        }
+    }
+
+    private void SearchBox_TextChanged(object? sender, RoutedEventArgs e)
+    {
+        if (AssociatedObject is null)
+        {
+            return;
+        }
+
+        var query = SearchBox?.Text?.ToLowerInvariant() ?? string.Empty;
+        var visibleCount = 0;
+        var tabItems = AssociatedObject.Items.OfType<TabItem>().ToList();
+
+        foreach (var item in tabItems)
+        {
+            var header = item.Header?.ToString()?.ToLowerInvariant() ?? string.Empty;
+            var visible = header.Contains(query);
+            item.IsVisible = visible;
+            if (visible)
+            {
+                visibleCount++;
+            }
+        }
+
+        AssociatedObject.SelectedItem = tabItems.FirstOrDefault(x => x.IsVisible);
+
+        if (NoMatchesControl is not null)
+        {
+            NoMatchesControl.IsVisible = visibleCount == 0;
+        }
+    }
+}