AmbientAttribute Class

Definition

Namespace:

System.Windows.Markup

Assembly:

System.Xaml.dll

Specifies that a property or type should be treated as ambient. The ambient concept relates to how XAML processors determine type owners of members.

public ref class AmbientAttribute sealed : Attribute

[System.AttributeUsage(System.AttributeTargets.Class | System.AttributeTargets.Method | System.AttributeTargets.Property, Inherited=true)]
public sealed class AmbientAttribute : Attribute

[<System.AttributeUsage(System.AttributeTargets.Class | System.AttributeTargets.Method | System.AttributeTargets.Property, Inherited=true)>]
type AmbientAttribute = class
    inherit Attribute

Public NotInheritable Class AmbientAttribute
Inherits Attribute

Inheritance

Object

Attribute

AmbientAttribute

Attributes

AttributeUsageAttribute

Remarks

An ambient property is a property where the value is expected to be available in the parser context when creating an object graph, but where typical type-member lookup is suspended for purposes of the immediate XAML node set being created. There are two main scenarios for the ambient concept:

• Some other property of the same object influences and qualifies how that object-property lookup should work.

• The property represents a larger deferral mechanism and the ambient capabilities for looking up a member value extend to all objects contained within the current object.

This attribute can be applied to specific properties that have expected containers that enable an ambient property lookup behavior, or can be applied to a class to enable the ambient property behavior in all cases of that value type for a property.

AmbientAttribute can also be applied to a CLR method, to support attributing a XAML attachable property as ambient. This is potentially necessary because in a CLR implementation a XAML attached property is implemented/represented to reflection as an accessor pattern with get and set methods. No actual CLR property to attribute exists, so restricting usage for AttributeTargets to Property would not have enabled specifying an attachable member as ambient. For an attachable member that you want to report as ambient, attribute the get accessor. You should not attempt to attribute methods that are not specifically support methods of attachable members.

In previous versions of the .NET Framework, this class existed in the WPF-specific assembly WindowsBase. In .NET Framework 4, AmbientAttribute is in the System.Xaml assembly. For more information, see Types Migrated from WPF to System.Xaml.

Ambient types (types where AmbientAttribute is applied at type level) can be used for certain XAML processing situations where the type of a property needs to be resolved out of order.

Object Writer Scenarios

If you are defining a XAML object writer, and you encounter a property, method or type where AmbientAttribute is applied, you typically must access a service to determine the intended ambient property lookup behavior that is needed for writing out objects. For more information, see IAmbientProvider.

Value Converters

Type converters or markup extensions might need to know the ambient information in order to process properties that represent indirect type mappings, such as properties that specify members or types by string names with or without qualification. In this scenario, AmbientAttribute is not intended to be used directly for value converter code logic. Rather, the value converter should rely on the XAML writer processing behavior, which will pass IAmbientProvider in its service contexts to your value converter methods when called.

WPF Scenarios for AmbientAttribute

• A property of a Style (TargetType) can qualify the necessary property name lookups that are needed to find the backing references for property names in Setter.Property values.

• All content within a Resources property (items of a ResourceDictionary) as well as template content, should be able to access other peers as values. Declaring the entire Resources property as ambient invokes logic that enables this in the WPF XAML parser.

See ResourceDictionary for an example of a scenario for setting AmbientAttribute at type level.

Constructors

AmbientAttribute()

Initializes a new instance of the AmbientAttribute class.

Properties

TypeId

When implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute)

Methods

Equals(Object)	Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute)
GetHashCode()	Returns the hash code for this instance. (Inherited from Attribute)
GetType()	Gets the Type of the current instance. (Inherited from Object)
IsDefaultAttribute()	When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute)
Match(Object)	When overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
ToString()	Returns a string that represents the current object. (Inherited from Object)

See also

• IsAmbient
• XamlMember
• IAmbientProvider
• XAML-related CLR attributes for custom types and libraries
• Define custom types for use with .NET XAML Services
• XAML Services