Articolo
11/18/2011

DependencyObject Class

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Represents an object that participates in the Silverlight dependency property system. DependencyObject is the immediate base class of several other important Silverlight classes, such as UIElement, Geometry, FrameworkTemplate, Style, and ResourceDictionary.

Inheritance Hierarchy

System.Object
System.Windows.DependencyObject
More...

Namespace: System.Windows
Assembly: System.Windows (in System.Windows.dll)

Syntax

'Declaration
Public MustInherit Class DependencyObject

public abstract class DependencyObject

The DependencyObject type exposes the following members.

Constructors

	Name	Description
	DependencyObject	Initializes a new instance of the DependencyObject class.

Top

Properties

	Name	Description
	Dispatcher	Gets the Dispatcher this object is associated with.

Top

Methods

	Name	Description
	CheckAccess	Determines whether the calling thread has access to this object.
	ClearValue	Clears the local value of a dependency property.
	Equals(Object)	Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetAnimationBaseValue	Returns any base value established for a Silverlight dependency property, which would apply in cases where an animation is not active.
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	GetValue	Returns the current effective value of a dependency property from a DependencyObject.
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	ReadLocalValue	Returns the local value of a dependency property, if a local value is set.
	SetValue	Sets the local value of a dependency property on a DependencyObject.
	ToString	Returns a string that represents the current object. (Inherited from Object.)

Top

Remarks

The DependencyObject class enables Silverlight dependency property system services on its many derived classes. For an overview of the dependency property concept, see Dependency Properties Overview.

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, whereas DependencyObject as a base class enables objects to use and set the dependency properties.

DependencyObject services and characteristics include the following:

Dependency property hosting support.
Custom 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 DependencyObject class. Also, the ownerType parameter of Register must be the type of your DependencyObject.
Attached property hosting support.
Custom attached property hosting support. You register a dependency property for the attached property usage by calling the RegisterAttached method, and storing the method's return value as a public static field in your class.
Get and set utility methods for values of any dependency properties that exist on the DependencyObject.
Dispatcher APIs for advanced threading scenarios.
Basic data binding and styling support, by enabling properties to be set as expressions to be evaluated at some later point in an object's lifetime..

It is not typical to derive directly from DependencyObject for most application scenarios. Instead you might derive from a specific control, from one of the control base classes (ContentControl; Control; ItemsControl), from FrameworkElement, or from non-control classes that still participate in UI such as Panel or Grid. Deriving from DependencyObject might be appropriate if you are defining a business or data storage object where you want dependency properties to be active, or if you are creating a service support class that will own attached properties. However, for basic data objects, you might instead implement the interface INotifyPropertyChanged, because by implementing the interface you could base your data on any object. For more information, see Data Binding.

Version Notes

In Silverlight 4 and later, DependencyObject dependency properties can be the target of a data binding. In XAML, you can specify a Binding attribute value for such properties, just like any other case where data binding a property is supported on FrameworkElement. However, DependencyObject does not implement DataContext or SetBinding. Thus, in order to inherit a data context, there must be a containing FrameworkElement that defines that data context. For more information, see Data Binding or Dependency Properties Overview.

If you are specifically targeting Silverlight 3, a property must be a FrameworkElement dependency property in order to be a binding target.

Examples

The following example defines a class that derives from DependencyObject, and defines an attached property along with the identifier field. The scenario for this class is that it is a service class that declares an attached property that other UI elements can set in XAML, and the service potentially acts on the attached property values on those UI elements at run time.

public abstract class AquariumServices : DependencyObject
{
    public enum Bouyancy {Floats,Sinks,Drifts}

    public static readonly DependencyProperty BouyancyProperty = DependencyProperty.RegisterAttached(
      "Bouyancy",
      typeof(Bouyancy),
      typeof(AquariumServices),
      new PropertyMetadata(Bouyancy.Floats)
    );
    public static void SetBouyancy(DependencyObject element, Bouyancy value)
    {
        element.SetValue(BouyancyProperty, value);
    }
    public static Bouyancy GetBouyancy(DependencyObject element)
    {
        return (Bouyancy)element.GetValue(BouyancyProperty);
    }
}

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Inheritance Hierarchy

Condividi tramite

DependencyObject Class

Inheritance Hierarchy

Syntax

Constructors

Properties

Methods

Remarks

Version Notes

Examples

Version Information

Silverlight

Silverlight for Windows Phone

Platforms

Thread Safety

See Also

Reference

Other Resources

Inheritance Hierarchy

Risorse aggiuntive