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DependencyObject.GetValue, méthode

Returns the current effective value of a dependency property on this instance of a DependencyObject.

Espace de noms: System.Windows
Assembly : WindowsBase (dans windowsbase.dll)

public Object GetValue (
	DependencyProperty dp
)
public Object GetValue (
	DependencyProperty dp
)
public function GetValue (
	dp : DependencyProperty
) : Object
Vous ne pouvez pas utiliser des méthodes dans XAML.

Paramètres

dp

The DependencyProperty identifier of the property to retrieve the value for.

Valeur de retour

Returns the current effective value.

Type d'exceptionCondition

InvalidOperationException

The specified dp or its value were invalid, or the specified dp does not exist.

The effective value is the value of the property that is returned by the property system to any caller that is requesting the value. The effective value is the result of the property system having evaluated all the possible inputs that participate in the property system value precedence. For more information, see Dependency Property Value Precedence.

This method will never return UnsetValue.

If you are not sure what the property's type should be, you can query the identifier of the requested dependency property to determine whether there is a more specific PropertyType that the return value can be converted to.

This example shows how to back a common language runtime (CLR) property with a DependencyProperty field, thus defining a dependency property. When you define your own properties and want them to support many aspects of Windows Presentation Foundation (WPF) functionality, including styles, data binding, inheritance, animation, and default values, you should implement them as a dependency property.

The following example first registers a dependency property by calling the Register method. The name of the identifier field that you use to store the name and characteristics of the dependency property must be the Name you chose for the dependency property as part of the Register call, appended by the literal string Property. For instance, if you register a dependency property with a Name of Location, then the identifier field that you define for the dependency property must be named LocationProperty.

In this example, the name of the dependency property and its CLR accessor is State; the identifier field is StateProperty; the type of the property is Boolean; and the type that registers the dependency property is MyStateControl.

If you fail to follow this naming pattern, designers might not report your property correctly, and certain aspects of property system style application might not behave as expected.

You can also specify default metadata for a dependency property. This example registers the default value of the State dependency property to be false.

public class MyStateControl : ButtonBase
{
  public MyStateControl() : base() { }
  public Boolean State
  {
    get { return (Boolean)this.GetValue(StateProperty); }
    set { this.SetValue(StateProperty, value); } 
  }
  public static readonly DependencyProperty StateProperty = DependencyProperty.Register(
    "State", typeof(Boolean), typeof(MyStateControl),new PropertyMetadata(false));
}

For the complete sample, see Custom Classes with Dependency Properties Sample.

For more information about how and why to implement a dependency property, as opposed to just backing a CLR property with a private field, see Dependency Properties Overview.

Davantage de code

How to: Register an Attached Property

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

Microsoft .NET Framework 3.0 est pris en charge sur Windows Vista, Microsoft Windows XP SP2 et Windows Server 2003 SP1.

.NET Framework

Prise en charge dans : 3.0

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