Add ObservableTriggerBehavior sample page

README.md

@@ -770,6 +770,8 @@ This section provides an overview of all available classes and their purpose in
 
 - **NavigateAndReset**
   *Navigates to a view model and clears the navigation stack.*
+- **ObservableTriggerBehavior**
+  *Subscribes to an `IObservable` and executes actions whenever the observable emits a value.*
 
 ### TextBox
 - **TextBoxSelectAllOnGotFocusBehavior**  

samples/BehaviorsTestApplication/Views/MainView.axaml

@@ -115,6 +115,9 @@
     <TabItem Header="ExecuteScriptAction">
       <pages:ExecuteScriptActionView />
     </TabItem>
+    <TabItem Header="Observable Trigger">
+      <pages:ObservableTriggerBehaviorView />
+    </TabItem>
     <TabItem Header="Reactive Navigation">
       <pages:ReactiveNavigationView />
     </TabItem>

samples/BehaviorsTestApplication/Views/Pages/ValueChangedTriggerBehaviorView.axaml

@@ -13,9 +13,9 @@
     <TextBlock Name="Text" HorizontalAlignment="Center" VerticalAlignment="Center">
       <Interaction.Behaviors>
         <ValueChangedTriggerBehavior Binding="{Binding Values^}">
-          <ChangePropertyAction TargetObject="Text" 
-                                   PropertyName="Text"
-                                   Value="{Binding Values^, StringFormat={} Value: {0}}" />
+          <ChangePropertyAction TargetObject="Text"
+                                PropertyName="Text"
+                                Value="{Binding Values^, StringFormat={} Value: {0}}" />
         </ValueChangedTriggerBehavior>
       </Interaction.Behaviors>
     </TextBlock>

samples/BehaviorsTestApplication/Views/ReactiveUI/ObservableTriggerBehaviorView.axaml

@@ -0,0 +1,28 @@
+<UserControl x:Class="BehaviorsTestApplication.Views.Pages.ObservableTriggerBehaviorView"
+             xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:vm="using:BehaviorsTestApplication.ViewModels"
+             x:DataType="vm:MainWindowViewModel"
+             mc:Ignorable="d" d:DesignWidth="600" d:DesignHeight="450">
+  <Design.DataContext>
+    <vm:MainWindowViewModel />
+  </Design.DataContext>
+  <Grid>
+    <TextBlock Name="Text"
+               FontSize="20"
+               HorizontalAlignment="Center"
+               VerticalAlignment="Center">
+      <Interaction.Behaviors>
+        <ObservableTriggerBehavior x:Name="Observer"
+                                   x:TypeArguments="x:Int32"
+                                   Observable="{Binding Values}">
+          <ChangePropertyAction TargetObject="Text"
+                                 PropertyName="Text"
+                                 Value="{Binding #Observer.Value, StringFormat={} Value: {0}}" />
+        </ObservableTriggerBehavior>
+      </Interaction.Behaviors>
+    </TextBlock>
+  </Grid>
+</UserControl>

samples/BehaviorsTestApplication/Views/ReactiveUI/ObservableTriggerBehaviorView.axaml.cs

@@ -0,0 +1,18 @@
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace BehaviorsTestApplication.Views.Pages;
+
+public partial class ObservableTriggerBehaviorView : UserControl
+{
+    public ObservableTriggerBehaviorView()
+    {
+        InitializeComponent();
+    }
+
+    private void InitializeComponent()
+    {
+        AvaloniaXamlLoader.Load(this);
+    }
+}
+

src/Avalonia.Xaml.Interactions.Custom/Core/ObservableTriggerBehavior.cs

@@ -0,0 +1,100 @@
+using System;
+using Avalonia.Reactive;
+using Avalonia.Threading;
+using Avalonia.Xaml.Interactivity;
+
+namespace Avalonia.Xaml.Interactions.Custom;
+
+/// <summary>
+/// A trigger that subscribes to an <see cref="IObservable{T}"/> and executes its actions whenever a new value is produced.
+/// The emitted value is exposed through the <see cref="Value"/> property and passed to the actions as a parameter.
+/// </summary>
+/// <typeparam name="T">The type of the observable sequence.</typeparam>
+public class ObservableTriggerBehavior<T> : StyledElementTrigger
+{
+    /// <summary>
+    /// Identifies the <seealso cref="Observable"/> avalonia property.
+    /// </summary>
+    public static readonly StyledProperty<IObservable<T>?> ObservableProperty =
+        AvaloniaProperty.Register<ObservableTriggerBehavior<T>, IObservable<T>?>(nameof(Observable));
+
+    /// <summary>
+    /// Identifies the <seealso cref="Value"/> avalonia property.
+    /// </summary>
+    public static readonly StyledProperty<T?> ValueProperty =
+        AvaloniaProperty.Register<ObservableTriggerBehavior<T>, T?>(nameof(Value));
+
+    private IDisposable? _subscription;
+
+    /// <summary>
+    /// Gets or sets the observable sequence that triggers the actions. This is an avalonia property.
+    /// </summary>
+    public IObservable<T>? Observable
+    {
+        get => GetValue(ObservableProperty);
+        set => SetValue(ObservableProperty, value);
+    }
+
+    /// <summary>
+    /// Gets the last value received from the <see cref="Observable"/>. This is an avalonia property.
+    /// </summary>
+    public T? Value
+    {
+        get => GetValue(ValueProperty);
+        private set => SetCurrentValue(ValueProperty, value);
+    }
+
+    /// <inheritdoc />
+    protected override void OnAttached()
+    {
+        base.OnAttached();
+        Subscribe();
+    }
+
+    /// <inheritdoc />
+    protected override void OnDetaching()
+    {
+        base.OnDetaching();
+        _subscription?.Dispose();
+        _subscription = null;
+    }
+
+    /// <inheritdoc />
+    protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
+    {
+        base.OnPropertyChanged(change);
+
+        if (change.Property == ObservableProperty)
+        {
+            Subscribe();
+        }
+    }
+
+    private void Subscribe()
+    {
+        _subscription?.Dispose();
+        var observable = Observable;
+        if (observable is not null)
+        {
+            _subscription = observable
+                .Subscribe(new AnonymousObserver<T>(value =>
+                {
+                    Dispatcher.UIThread.Invoke(() =>
+                    {
+                        Value = value;
+                        Execute(value);
+                    });
+                }));
+        }
+    }
+
+    private void Execute(object? parameter)
+    {
+        if (AssociatedObject is null || !IsEnabled)
+        {
+            return;
+        }
+
+        Interaction.ExecuteActions(AssociatedObject, Actions, parameter);
+    }
+}