< Application x:Class="WpfApplication1.App"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    StartupUri="Window1.xaml" >
    < Application.Resources >

    < /Application.Resources >
< /Application >

But what if you want to use a window from another project (class library)? The pack URI scheme, used by WPF, allows you to identify and load files from:

• the current assembly
• a referenced assembly
• a location relative to an assembly
• the site of origin for the application

The format of the pack URI is pack://authority/path. The authority identifies the type of package and the path the location of a part inside a package. There are two authorities supported by WPF:

• application:/// identifies application data files (known at compile time)
• siteoforigin:/// identifies site of origin files

To use resource files from a referenced assembly you need to use the application:/// authority, and the path must have the form AssemblyShortName[;Version][;PublicKey];component/Path. Version and PublicKey are optional.

Let’s say you want to use a XAML called SampleWindow.xaml from a referenced assembly called WpfDemoLib. The App.xaml file should look like this:

< Application x:Class="WpfApplication1.App"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    StartupUri="pack://application:,,,/WpfDemoLib;component/SampleWindow.xaml" >
    < Application.Resources >

    < /Application.Resources >
< /Application >

You can learn more about pack URIs in WPF from MSDN.