Some URI Properties
Often, in WPF/Silverlight there are objects with a Source property – Frame, Image, ResourceDictionary, and NavigationWindow are some of them – which enable you to refer to an image or another XAML file to load.
IUriContext
XAML/WPF introduced IUriContext, which is used in 2 ways by XAML:
- Any object that implements IUriContext will have IUriContext.BaseUri set during XAML/BAML load.
- Any type converter or markupextension can access IUriContext as one of the 3 service providers available in .NET 3.x to type converters or markup extensions.
For properties of type Uri, the Uri type converter helps convert the specified uri string into a Uri object. The UriConverter is not aware of IUriContext, so your component may need to combine the IUriContext.BaseUri with the relative Uri specified as the Source property.
xml:base
In .NET 3, XAML doesn’t support xml:base to set a different base Uri. Current builds of .NET 4 do…
xml:base=”http://someplace.com”
Tooling Difficulty
Since some properties (Image.Source) have XAML text syntaxes which allow a URI, but aren’t of type System.Uri, there is currently no way for XAML based tools to understand the complete set of properties that can take a URI text syntax. We hope to address this in the future. For now, tools need to hard code the fact that there are several type converters that really just want to take a URI text syntax.
Type Converters that support URI text syntax:
(I’ll grow this list over time)
Why this came up
Mike Shim (a PM on the XAML team) and I were discussing options for a bug in .NET 4 that came our way yesterday…NavigationWindow was relying on an attached property for the BaseUri…instead of IUriContext. For now, we plan to fix NavigationWindow to use IUriContext…and determine the complete solution for v3 compat with the attached property next milestone.
Summary
Given this info, you should be able to build a XAML Vocabulary which uses relative Uris…or just understand how WPF does it.
Related Content
Ashish Shetty describing Resources in WPF Applications and Silverlight 2: Demystifying URI references for app resources
MSDN: Pack URIs in WPF
Shawn Wildermuth’s Silverlight XAML Relative URI’s and “Site of Origin”