/// <summary>
/// Registers a notification function for listening to changes to a tree of DependencyProperties relative to this DependencyObject instance.
/// </summary>
/// <param name="instance">The DependencyObject instance the dependency property tree starts at.</param>
/// <param name="callback">A callback based on the PropertyChangedCallback delegate, which the system invokes when the value of any of the specified properties changes.</param>
/// <param name="properties">The tree of dependency property to register for property-changed notification.</param>
/// <returns>A disposable that will unregister the callback when disposed.</returns>
/// <remarks>
/// <para>Each node of the dependency property tree is represented by an array describing the path of the dependency property relative to the given dependency object instance.</para>
/// <para>For example, to register for notifications to changes to the Color of a TextBlock's Foreground:</para>
/// <code>var disposable = myTextBlock.RegisterDisposableNestedPropertyChangedCallback(callback, new [] { TextBlock.ForegroundProperty, SolidColorBrush.ColorProperty });</code>
/// </remarks>
internal static IDisposable RegisterDisposableNestedPropertyChangedCallback(this DependencyObject instance, PropertyChangedCallback callback, params DependencyProperty[][] properties)
{
if (instance == null)
{
return(Disposable.Empty);
}
return(properties
.Where(Enumerable.Any)
.GroupBy(Enumerable.First, propertyPath => propertyPath.Skip(1).ToArray())
.Where(Enumerable.Any)
.Where(group => group.Key != null)
.Select(group =>
{
var property = group.Key;
var subProperties = group.ToArray();
// Validate the property owner type
if (!instance.GetType().Is(property.OwnerType) && !property.IsAttached)
{
return Disposable.Empty;
}
var childDisposable = new SerialDisposable();
childDisposable.Disposable = (instance.GetValue(property) as DependencyObject)?.RegisterDisposableNestedPropertyChangedCallback(callback, subProperties);
var disposable = instance.RegisterDisposablePropertyChangedCallback(property, (s, e) =>
{
callback(s, e);
childDisposable.Disposable = s?.RegisterDisposableNestedPropertyChangedCallback(callback, subProperties);
});
return new CompositeDisposable(disposable, childDisposable);
})
.Apply(disposables => new CompositeDisposable(disposables)));
}