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How to: Register an Attached Property

  • Article

This example shows how to register an attached property and provide public accessors so that you can use the property in both XAML and code. Attached properties are a syntax concept defined by XAML. Most attached properties for WPF types are also implemented as dependency properties. You can use dependency properties on any DependencyObject types.

Example

The following example shows how to register an attached property as a dependency property, by using the RegisterAttached method. The provider class has the option of providing default metadata for the property that is applicable when the property is used on another class, unless that class overrides the metadata. In this example, the default value of the IsBubbleSource property is set to false.

The provider class for an attached property (even if it is not registered as a dependency property) must provide static get and set accessors that follow the naming convention Set[AttachedPropertyName] and Get[AttachedPropertyName]. These accessors are required so that the acting XAML reader can recognize the property as an attribute in XAML and resolve the appropriate types.

public static readonly DependencyProperty IsBubbleSourceProperty = DependencyProperty.RegisterAttached(
  "IsBubbleSource",
  typeof(Boolean),
  typeof(AquariumObject),
  new FrameworkPropertyMetadata(false, FrameworkPropertyMetadataOptions.AffectsRender)
);
public static void SetIsBubbleSource(UIElement element, Boolean value)
{
  element.SetValue(IsBubbleSourceProperty, value);
}
public static Boolean GetIsBubbleSource(UIElement element)
{
  return (Boolean)element.GetValue(IsBubbleSourceProperty);
}

Public Shared ReadOnly IsBubbleSourceProperty As DependencyProperty = DependencyProperty.RegisterAttached("IsBubbleSource", GetType(Boolean), GetType(AquariumObject), New FrameworkPropertyMetadata(False, FrameworkPropertyMetadataOptions.AffectsRender))
Public Shared Sub SetIsBubbleSource(ByVal element As UIElement, ByVal value As Boolean)
    element.SetValue(IsBubbleSourceProperty, value)
End Sub
Public Shared Function GetIsBubbleSource(ByVal element As UIElement) As Boolean
    Return CType(element.GetValue(IsBubbleSourceProperty), Boolean)
End Function

See also