DependencyProperty.RegisterAttachedReadOnly Method (String, Type, Type, PropertyMetadata, ValidateValueCallback)

Registers a read-only attached property, with the specified property type, owner type, property metadata, and a validation callback.

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

public static DependencyPropertyKey RegisterAttachedReadOnly(
	string name,
	Type propertyType,
	Type ownerType,
	PropertyMetadata defaultMetadata,
	ValidateValueCallback validateValueCallback
)

Parameters

name
Type: System.String

The name of the dependency property to register.

propertyType
Type: System.Type

The type of the property.

ownerType
Type: System.Type

The owner type that is registering the dependency property.

defaultMetadata
Type: System.Windows.PropertyMetadata

Property metadata for the dependency property.

validateValueCallback
Type: System.Windows.ValidateValueCallback

A reference to a user-created callback that should perform any custom validation of the dependency property value beyond typical type validation.

Return Value

Type: System.Windows.DependencyPropertyKey
A dependency property key that should be used to set the value of a static read-only field in your class, which is then used to reference the dependency property.

This method returns the type DependencyPropertyKey, whereas RegisterAttached returns the type DependencyProperty. Typically, the keys that represent the type DependencyProperty. Typically, the keys that represent read-only properties are not made public, because the keys can be used to set the dependency property value by calling SetValue(DependencyPropertyKey, Object). Your class design will affect your requirements, but it is generally recommended to limit the access and visibility of any DependencyPropertyKey to only those parts of your code that are necessary to set that dependency property as part of class or application logic. It is also recommended that you expose a dependency property identifier for the read-only dependency property, by exposing the value of DependencyPropertyKey.DependencyProperty as a public static readonly field on your class.

Read-only attached properties are a rare scenario, because the primary scenario for an attached property is its use in XAML. Without a public setter, an attached property cannot be set in XAML syntax.

For more information on dependency property registration, see DependencyProperty.

Use RegisterAttached for Value-inheriting Dependency Properties

One particular scenario for registering a dependency property as attached instead of Register is to support property value inheritance. You should register value-inheriting dependency properties with RegisterAttached even if the class defines property wrapper accessors that expose the dependency property, and even if you do not intend to expose Get* and Set* static methods to provide true attached property support accessors. Although property value inheritance might appear to work for nonattached dependency properties, the inheritance behavior for a nonattached property through certain element boundaries in the runtime tree is undefined. Registering the property as attached effectively makes the attached property a global property to the property system, and assures that property value inheritance works across all boundaries in an element tree. Always use RegisterAttached to register properties where you specify Inherits in the metadata. For more information, see Property Value Inheritance.

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, 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.

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