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x:Uid Directive

Provides a unique identifier for markup elements. In many scenarios, this unique identifier is used by XAML localization processes and tools.

<object x:Uid="identifier"... />

identifier

A manually created or autogenerated string that should be unique in a file when it is interpreted by an x:Uid consumer.

In [MS-XAML], x:Uid is defined as a directive. For more information, see [MS-XAML] Section 5.3.6.

x:Uid is discrete from x:Name both because of the stated XAML localization scenario and so that identifiers that are used for localization have no dependencies on the programming model implications of x:Name. Also, x:Name is governed by the XAML namescope; however, x:Uid is not governed by any XAML language defined concept of uniqueness enforcement. XAML processors in a broad sense (processors that are not part of the localization process) are not expected to enforce uniqueness of x:Uid values. That responsibility is conceptually on the originator of the values. The expectation of uniqueness of x:Uid values within a single XAML source is reasonable for consumers of the values, such as dedicated globalization processes or tools. The typical uniqueness model is that x:Uid values are unique within an XML-encoded file that represents XAML.

Tools that have significant knowledge of a particular XAML schema can choose to apply x:Uid only for true localizable strings, instead of for all cases where a text string value is encountered in markup.

Frameworks can specify a particular property in their object model to be an alias for x:Uid by applying the attribute UidPropertyAttribute to the defining type. If a framework specifies a particular property, it is not valid to specify both x:Uid and the aliased member on the same object. If both x:Uid and the aliased member are specified, the .NET Framework XAML Services API typically throws XamlDuplicateMemberException for this case.

For more information about the role of x:Uid in the WPF localization process and in the BAML form of XAML, see Globalization for WPF or Uid

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