I am trying to create dynamic tabs in WPF, and I'm trying to write a content template that will only apply to some tab items. I want to be able to create an identifier for the content template so that I can reference it in the code behind, and so that I can selectively apply it to only some tabs in a single TabControl. However, I am confused about these three different xaml identifiers. What is the difference, and which one is best for my purposes?
The 'x:' specifies the namespace, which would in your case most likely be "http://schemas.microsoft.com/winfx/2006/xaml" You will see the alias declared at the top of your Window.Xaml file. x:Key, x:Name, etc are all directives in that namespace.
In contrast, the 'Name' attribute (without the x:) is a dependency property declared in the FrameworkElement class.
x:Key
Uniquely identifies elements that are created and referenced in a XAML-defined dictionary. Adding an x:Key value to a XAML object element is the most common way to identify a resource in a resource dictionary, for example in a WPF ResourceDictionary.
x:Name
Uniquely identifies XAML-defined elements in a XAML namescope. XAML namescopes and their uniqueness models can be applied to the instantiated objects, when frameworks provide APIs or implement behaviors that access the XAML-created object graph at run time.
x:Uid
Provides a unique identifier for markup elements. In many scenarios, this unique identifier is used by XAML localization processes and tools.
Notes
I have only seen x:Uid when a app must support different languages with a resource dictionary.
For the other two (x:Key and x:Name), a basic rule of thumb is to use x:Name for Framework elements and x:Key for styles, templates, and so on. So for your question, if you are naming a template itself, you would use the x:Key directive. Controls declared within the template would use the x:Name directive.
A complete list of all Xaml directives is given at Xaml Namespace