---
title: "x:Uid Directive"
ms.date: "03/30/2017"
helpviewer_keywords: 
  - "XAML [XAML Services], localizable content attribute"
  - "XAML [XAML Services], x:Uid attribute"
  - "x:Uid attribute [XAML Services]"
  - "Uid attribute [XAML Services]"
ms.assetid: 81defade-483b-4a89-b76d-9b25bba34010
---
# x:Uid Directive

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

## XAML Attribute Usage

```xaml
<object x:Uid="identifier"... />
```

## XAML Values

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

## Remarks

In [MS-XAML], `x:Uid` is defined as a directive. For more information, see [\[MS-XAML\] Section 5.3.6](/previous-versions/msp-n-p/ff650760(v=pandp.10)).

`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 <xref:System.Windows.Markup.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, .NET XAML Services API typically throws <xref:System.Xaml.XamlDuplicateMemberException> for this case.

## WPF Usage Notes

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](../framework/wpf/advanced/globalization-for-wpf.md) or <xref:System.Windows.Markup.Localizer.BamlLocalizableResourceKey.Uid%2A>

## See also

- <xref:System.Windows.Markup.Localizer.BamlLocalizableResourceKey.Uid%2A>
- <xref:Microsoft.Build.Tasks.Windows.UidManager>
- [Globalization for WPF](../framework/wpf/advanced/globalization-for-wpf.md)