Add new custom reactive event behaviors

Author: wieslawsoltes

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

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+using System.Reactive.Disposables;
+using Avalonia.Xaml.Interactivity;
+
+namespace Avalonia.Xaml.Interactions.Custom;
+
+/// <summary>
+/// A base class for behaviors using ActualThemeVariantChanged event.
+/// </summary>
+/// <typeparam name="T"></typeparam>
+public abstract class ActualThemeVariantChangedBehavior<T> : DisposingBehavior<T> where T : StyledElement
+{
+    private CompositeDisposable? _disposables;
+
+    /// <inheritdoc />
+    protected override void OnAttached(CompositeDisposable disposables)
+    {
+        _disposables = disposables;
+    }
+
+    /// <inheritdoc />
+    protected override void OnActualThemeVariantChangedEvent()
+    {
+        OnActualThemeVariantChangedEvent(_disposables!);
+    }
+
+    /// <summary>
+    /// Called when the <see cref="StyledElementBehavior{T}.AssociatedObject"/> ActualThemeVariantChanged event is raised.
+    /// </summary>
+    /// <param name="disposable">The group of disposable resources that are disposed together</param>
+    protected abstract void OnActualThemeVariantChangedEvent(CompositeDisposable disposable);
+}

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

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+using System.Reactive.Disposables;
+using Avalonia.Xaml.Interactivity;
+
+namespace Avalonia.Xaml.Interactions.Custom;
+
+/// <summary>
+/// A base class for behaviors using DataContextChanged event.
+/// </summary>
+/// <typeparam name="T"></typeparam>
+public abstract class DataContextChangedBehavior<T> : DisposingBehavior<T> where T : StyledElement
+{
+    private CompositeDisposable? _disposables;
+
+    /// <inheritdoc />
+    protected override void OnAttached(CompositeDisposable disposables)
+    {
+        _disposables = disposables;
+    }
+
+    /// <inheritdoc />
+    protected override void OnDataContextChangedEvent()
+    {
+        OnDataContextChangedEvent(_disposables!);
+    }
+
+    /// <summary>
+    /// Called when the <see cref="StyledElementBehavior{T}.AssociatedObject"/> DataContextChanged event is raised.
+    /// </summary>
+    /// <param name="disposable">The group of disposable resources that are disposed together</param>
+    protected abstract void OnDataContextChangedEvent(CompositeDisposable disposable);
+}

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

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+using System.Reactive.Disposables;
+using Avalonia.Xaml.Interactivity;
+
+namespace Avalonia.Xaml.Interactions.Custom;
+
+/// <summary>
+/// A base class for behaviors using Initialized event.
+/// </summary>
+/// <typeparam name="T"></typeparam>
+public abstract class InitializedBehavior<T> : DisposingBehavior<T> where T : StyledElement
+{
+    private CompositeDisposable? _disposables;
+
+    /// <inheritdoc />
+    protected override void OnAttached(CompositeDisposable disposables)
+    {
+        _disposables = disposables;
+    }
+
+    /// <inheritdoc />
+    protected override void OnInitializedEvent()
+    {
+        OnInitializedEvent(_disposables!);
+    }
+
+    /// <summary>
+    /// Called when the <see cref="StyledElementBehavior{T}.AssociatedObject"/> Initialized event is raised.
+    /// </summary>
+    /// <param name="disposable">The group of disposable resources that are disposed together</param>
+    protected abstract void OnInitializedEvent(CompositeDisposable disposable);
+}

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

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+using System.Reactive.Disposables;
+using Avalonia.Xaml.Interactivity;
+
+namespace Avalonia.Xaml.Interactions.Custom;
+
+/// <summary>
+/// A base class for behaviors using ResourcesChanged event.
+/// </summary>
+/// <typeparam name="T"></typeparam>
+public abstract class ResourcesChangedBehavior<T> : DisposingBehavior<T> where T : StyledElement
+{
+    private CompositeDisposable? _disposables;
+
+    /// <inheritdoc />
+    protected override void OnAttached(CompositeDisposable disposables)
+    {
+        _disposables = disposables;
+    }
+
+    /// <inheritdoc />
+    protected override void OnResourcesChangedEvent()
+    {
+        OnResourcesChangedEvent(_disposables!);
+    }
+
+    /// <summary>
+    /// Called when the <see cref="StyledElementBehavior{T}.AssociatedObject"/> ResourcesChanged event is raised.
+    /// </summary>
+    /// <param name="disposable">The group of disposable resources that are disposed together</param>
+    protected abstract void OnResourcesChangedEvent(CompositeDisposable disposable);
+}