ResourceDictionary in a separate assembly

Check out the pack URI syntax. You want something like this:

<ResourceDictionary Source="pack://application:,,,/YourAssembly;component/Subfolder/YourResourceFile.xaml"/>

An example, just to make this a 15 seconds answer -

Say you have "styles.xaml" in a WPF library named "common" and you want to use it from your main application project:

1. Add a reference from the main project to "common" project
2. Your app.xaml should contain:

---

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="pack://application:,,,/Common;component/styles.xaml"/>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Application.Resources>

---

I'm working with .NET 4.5 and couldn't get this working... I was using WPF Custom Control Library. This worked for me in the end...

<ResourceDictionary Source="/MyAssembly;component/mytheme.xaml" />

source: http://social.msdn.microsoft.com/Forums/en-US/wpf/thread/11a42336-8d87-4656-91a3-275413d3cc19