MarkupExtension Class

Provides a base class for XAML markup extension implementations that can be supported by .NET Framework XAML Services and its XAML readers and XAML writers.


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

public abstract class MarkupExtension

The MarkupExtension type exposes the following members.

Protected methodMarkupExtensionInitializes a new instance of a class derived from MarkupExtension.

Public methodProvideValueWhen implemented in a derived class, returns an object that is provided as the value of the target property for this markup extension.

Markup extensions return objects based on string attribute values or markup elements in XAML. Markup extensions return objects in a more sophisticated way than type converters alone can accomplish. A XAML object writer invokes a type converter because a type or member has a type converter implementation associated with it. From the CLR frame of reference, this means a type or member is TypeConverterAttribute attributed. From the XAML type system perspective, this means that a XAML type or a XAML member has a value for its TypeConverter property. The invocation of a type converter is tied to the type or property definition, and is always invoked for these cases. In contrast, a markup extension is more under the control of user code and user-produced markup, and can be applied when an application scenario demands it. A markup extension can be invoked and can be used for setting different type-member values so long as the markup extension's return type is assignable to that value.

For information on creating a custom markup extension, see ProvideValue. For more information on markup extensions in general, see Markup Extensions for XAML Overview. If you are building on WPF and using or creating markup extensions for XAML, other relevant information can be found in the topic Markup Extensions and WPF XAML.

The ProvideValue method of each markup extension implementation can use an IServiceProvider at run time that can provide context. This IServiceProvider is then queried for specific services that pass information, such as IProvideValueTarget or IXamlTypeResolver. For more information on service contexts for a markup extension, see Service Contexts Available to Type Converters and Markup Extensions.

Derived classes should be attributed with MarkupExtensionReturnTypeAttribute to inform consumers of the most specific return type available from the markup extension's ProvideValue implementation.

.NET Framework

Supported in: 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1




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