x: meaning in xaml

I see a lot statements like

<TextBox x:Name="txtInput" />

or like

<BooleanToVisibilityConverter x:Key="boolToVis" />

Why the x: is needed and what it gives me.

<DockPanel.Resources>
  <c:MyData x:Key="myDataSource"/>
</DockPanel.Resources>

And here we have also the c:

Thanks for help

It is nothing more than shortcuts to the different namespaces for XML. You can choose them as you like. If you look at the upper lines in your XAML you will find the line:

xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

Change the 'x' to 'wpf' for instance and you will see that you need to change all the 'x:' prefixes in your code to 'wpf:' to make it compile.

The 'c:' prefix references code of your own. Say you have a class library that compiles to MyLib.dll. This library contains a class named MyData. To be able to reference the MyData class you need something like:

xmlns:c="clr-namespace:MyClasses;assembly=MyLib"

in your XAML header.

You can then reference the MyData class in you XAML with c:MyData. But you are entirely free to change the 'c' to 'myfabulousclasses' or anything else you fancy.

The purpose of this? To distinguish classes or members that have the same name, but belong to different dll's.

The x: Prefix

In the previous root element example, the prefix x: was used to map the XAML namespace http://schemas.microsoft.com/winfx/2006/xaml, which is the dedicated XAML namespace that supports XAML language constructs. This x: prefix is used for mapping this XAML namespace in the templates for projects. The XAML namespace for the XAML language contain several programming constructs that you will use very frequently in your XAML. The following is a listing of the most common x: prefix programming constructs you will use:

x:Key: Sets a unique key for each resource in a ResourceDictionary (or similar dictionary concepts in other frameworks). x:Key will probably account for 90% of the x: usages you will see in a typical WPF application's markup.

x:Class: Specifies the CLR namespace and class name for the class that provides code-behind for a XAML page. You must have such a class to support code-behind per the WPF programming model, and therefore you almost always see x: mapped, even if there are no resources.

x:Name: Specifies a run-time object name for the instance that exists in run-time code after an object element is processed. In general, you will frequently use a WPF-defined equivalent property for x:Name. Such properties map specifically to a CLR backing property and are thus more convenient for application programming, where you frequently use run time code to find the named elements from initialized XAML. The most common such property is FrameworkElement.Name. You might still use x:Name when the equivalent WPF framework-level Name property is not supported in a particular type. This occurs in certain animation scenarios.

x:Static: Enables a reference that returns a static value that is not otherwise a XAML-compatible property.

x:Type: Constructs a Type reference based on a type name. This is used to specify attributes that take Type, such as Style.TargetType, although frequently the property has native string-to-Type conversion in such a way that the x:Type markup extension usage is optional.

http://msdn.microsoft.com/en-us/library/ms752059.aspx http://msdn.microsoft.com/en-us/library/ms753327.aspx

It is part of a namespace. In your example the c: prefix is used to indicate that the MyData tag belongs to this namespace. You may take a look at the following article on MSDN which explains the x: prefix in XAML.