Markup extensions and WPF XAML

This topic describes the markup extension concepts for XAML, including its syntax rules, purpose, and the underlying class object model. markup extensions are general features of the XAML language and. NET implementations of XAML Services. This topic deals specifically with markup extensions for WPF XAML.

This topic includes the following sections.

• XAML processors and markup extensions
• Basic markup Extension syntax
• Markup extensions for XAML definitions
• WPF-specific markup extensions
• *extension class
• Escape sequences and markup extensions
• Nested markup extensions in XAML usage
• Markup extension and Attribute element syntax
• Related Topics

XAML processors and markup extensions

Typically, a XAML parser can interpret an attribute value as a literal string that can be converted to a primitive, or you can convert an attribute value to an object in some way.One method is to reference a type converter; see the topic for detailsTypeConverters and XAML.However, there are situations where other behaviors are required. For example, you can instruct a XAML processor that the value of an attribute should not generate a new object in the object graph.  

Basic Markup Extension Syntax

You can implement markup extensions to provide values for properties in attribute usages and/or property element usages.

When used to provide an attribute value, the syntax for separating the markup extension sequence from the XAML processor area is the left and right curly braces ({and}). The type of the markup extension is then identified by a string token immediately following the opening brace.

When used in attribute element syntax, the markup extension looks the same as any other element that provides a property element value, that is, a XAML element declaration that refers to a markup extension class as an element and is enclosed in angle brackets (<>).

markup Extensions for XAML definitions

There are several markup extensions that are not specific to the WPF implementation of XAML, but are intrinsic or functional implementations of XAML in the form of a language.These markup extensions are implemented as part of a regular. NET Framework XAML Service in the System.Xaml assembly and are located in the XAML language XAML namespace.x:prefix in the usage. " For common markup usages, these markup extensions are usually identified by the   in the usage, and the x:  prefix.  markupextension base class (also defined in System.Xaml)  provides the pattern of all Markup extensions should use with order to is supported in XAML readers and XAML writers, including in WPF XAML. " The markupextension  base class (also defined in System.Xaml) provides the patterns that all markup extensions should use in order to be supported in XAML readers and XAML writers (including support in WPF XAML).

• x:type supplies the type object for the named Type. " > x:type  provides   for named types; type  objects.   This tool is most commonly used for styles and templates.  x:type Markup Extension. " > For more information, see   x:type Markup extension.

• x:static produces Static values. " > x:static  generate a static value.  x:static Markup Extension. " > For more information, see   x:static Markup extension.

• X:NULL Specifies null as a value for a property and can is used either for The attributes or property element values. > x:null  will   null  is specified as the value of the property, which can be used for attribute or attribute element values.  x:null Markup Extension." > For more information, see   x:null markup extension.

• X:array provides support for the creation of regular arrays in XAML syntax, in cases where the collection support provided by WPF base elements and control models is deliberately not used. For more information, see x:array Markup extension.

Description

x: A typical XAML namespace mapping used for XAML language intrinsics in a XAML file or in the root element of a production. x:mapping. " For example, the Visual Studio template for a WPF application uses this   x:  map to start the XAML file.  x:mapping as a means of identifying those entities that is a defined part of the XAML namespace for the XA ML language, as opposed to the WPF default namespace or other XAML namespaces does related to a specific framework. " > You can choose a different prefix tag in your own XAML namespace mapping, but this document will take the default   x:  the mapping, and it identifies XAML that belongs to the XAML language Those entities that have a defined portion of the namespace, as opposed to the WPF default namespace or other XAML namespaces that are not related to a particular framework.

WPF-specific markup extensions

The most common markup extensions in WPF programming are markup extensions (StaticResource and DynamicResource) that support resource references, and Markup Extensions (bindings) that support data binding.

• StaticResource provides a value for a property by replacing the value of the defined resource. StaticResource Calculations are eventually made when the XAML loads, and there is no permission to access the object graph at run time. For more information, see StaticResource Markup extension.

• DynamicResource provides a value for a property by deferring the value to a run-time reference to the resource. Dynamic resource references force a new lookup every time a resource is accessed and have access to the object graph at run time.to obtain this access, the dependency property in the WPF property system and the computed expression support the DynamicResource concept. therefore, for a dependency property target, you can only use DynamicResource. For more information, see DynamicResource Markup extension.

• The binding uses the data context that is applied to the parent object at run time to provide a data-bound value for the property.  This markup extension is relatively complex because it enables a large number of inline syntax to specify data binding. For more information, see Binding markup extensions.

• RelativeSource provides source information for Binding that can locate several possible relationships in the runtime object Tree . The markup extension above provides a dedicated source for bindings created in a multipurpose template, or for bindings created in code without fully understanding the surrounding object tree. For more information, see RelativeSource MarkupExtension.

• PassTemplateBinding, a control template can define the value of a templated property in a property from the object model of the class from which you want to take advantage of the template. templatebinding Markup Extension. " > For more information, see   TemplateBinding markup extension.  templatebinding, see styling with ControlTemplates Sample." For more information on the actual use of the   templatebinding , see  styling with ControlTemplates Sample (use ControlTemplates to set a style example).

• colorconvertedbitmap supports a relatively advanced imaging scenario. " The colorconvertedbitmap  supports a relatively advanced imaging scheme.  colorconvertedbitmap Markup Extension. " > For more information, see   colorconvertedbitmap markup extension.

• componentresourcekey and themedictionary support aspects of resource Lookup, particularly for resources and themes that is packaged with custom controls. " > componentresourcekey  and   themedictionary  supports various aspects of resource lookups, especially support for finding resources and topics packaged with custom controls.  componentresourcekey Markup Extension, themedictionary Markup Extension, or control Authoring Overview." > For more information, see ComponentResourceKey Markup Extensions, themedictionary markup extensions, or   Control Authoring Overview.

Markup extensions and WPF XAML