DependencyObject Class

The DependencyObject class enables Windows Presentation Foundation (WPF) property system services on its many derived classes.

The property system's primary function is to compute the values of properties, and to provide system notification about values that have changed. Another key class that participates in the property system is DependencyProperty. DependencyProperty enables the registration of dependency properties into the property system, and provides identification and information about each dependency property, whereas DependencyObject as a base class enables objects to use the dependency properties.

DependencyObject services and characteristics include the following:

• Dependency property hosting support. You register a dependency property by calling the Register method, and storing the method's return value as a public static field in your class.

• Attached property hosting support. You register an attached property by calling the RegisterAttached method, and storing the method's return value as a public static read-only field in your class. (There are also additional member requirements; note that this represents a WPF specific implementation for attached properties. For details, see Attached Properties Overview.) Your attached property can then be set on any class that derives from DependencyObject.

• Get, set, and clear utility methods for values of any dependency properties that exist on the DependencyObject.

• Metadata, coerce value support, property changed notification, and override callbacks for dependency properties or attached properties. Also, the DependencyObject class facilitates the per-owner property metadata for a dependency property.

• A common base class for classes derived from ContentElement, Freezable, or Visual. (UIElement, another base element class, has a class hierarchy that includes Visual.)

The following example derives from DependencyObject to create a new abstract class. The class then registers an attached property and includes support members for that attached property.

public abstract class AquariumObject3 : DependencyObject
{
    public enum Bouyancy
    {
        Floats,
        Sinks,
        Drifts
    }
    public static readonly DependencyProperty BouyancyProperty = DependencyProperty.RegisterAttached(
      "Bouyancy",
      typeof(Bouyancy),
      typeof(AquariumObject3),
      new FrameworkPropertyMetadata(Bouyancy.Floats, FrameworkPropertyMetadataOptions.AffectsArrange),
      new ValidateValueCallback(ValidateBouyancy)
    );
    public static void SetBouyancy(UIElement element, Bouyancy value)
    {
        element.SetValue(BouyancyProperty, value);
    }
    public static Bouyancy GetBouyancy(UIElement element)
    {
        return (Bouyancy)element.GetValue(BouyancyProperty);
    }
    private static bool ValidateBouyancy(object value)
    {
        Bouyancy bTest = (Bouyancy) value;
        return (bTest == Bouyancy.Floats || bTest == Bouyancy.Drifts || bTest==Bouyancy.Sinks);
    }
    public static readonly DependencyProperty IsDirtyProperty = DependencyProperty.Register(
      "IsDirty",
      typeof(Boolean),
      typeof(AquariumObject3)
    );
}

.NET Framework

.NET Framework Client Profile

Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Reference

Other Resources