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DependencyPropertyKey Class

Provides a dependency property identifier for limited write access to a read-only dependency property.

Namespace:  System.Windows
Assembly:  WindowsBase (in WindowsBase.dll)
public sealed class DependencyPropertyKey
You cannot directly create an instance of this class in XAML.

DependencyPropertyKey instances are obtained as the return value of a dependency property registration call using the methods RegisterReadOnly or RegisterAttachedReadOnly.

The types that register a dependency property can use the DependencyPropertyKey in calls to SetValue and ClearValue that adjust the property's value as part of class logic. If permitted by the access level of the key, related classes can use the key and the dependency property also. For instance, you can declare the key as internal, and other types within the same assembly can also set that dependency property.

The DependencyPropertyKey returned by read-only dependency property registration should not be made public, because exposing the key makes the property settable, thus defeating the point of registering it as a read-only dependency property. Also, exposing the key causes a mismatch between the available dependency property behaviors and its common language runtime (CLR) property wrapper implementations, which is bad class design.

Instead of exposing the key itself, you should instead expose the DependencyProperty value of the DependencyPropertyKey as a public static readonly DependencyProperty on your class. This enables the property to return a valid dependency property identifier for certain property system operations such as enumerating locally set values. However, the identifier thus obtained does not have the full capabilities of a DependencyProperty for many property system operations.

The following example registers a read-only dependency property, and also uses the key for two purposes in other class members: implementing the get "wrapper", and as the identifier for a protected determination operation that sets the value based on calculations of other property values.

internal static readonly DependencyPropertyKey AquariumSizeKey = DependencyProperty.RegisterReadOnly(
  "AquariumSize",
  typeof(double),
  typeof(Aquarium),
  new PropertyMetadata(double.NaN)
);
public static readonly DependencyProperty AquariumSizeProperty =
  AquariumSizeKey.DependencyProperty;
public double AquariumSize
{
  get { return (double)GetValue(AquariumSizeProperty); }
}
System.Object
  System.Windows.DependencyPropertyKey
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

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

.NET Framework

Supported in: 3.5, 3.0
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