Coming from the WPF world, finding out that Silverlight lacked the feature of distributing application resources among separate files was one of those kick in a head moments. Well, not anymore. Silverlight 3, like its big brother WPF, now supports partitioning resources through merged dictionaries.

Merged resource dictionaries can be included as external files (build action = Content), as included resources (build action = Resource), or as referenced assembly resources (e.g. theming).

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="Themes/Theme1.xaml" />
            <ResourceDictionary Source="Themes/Theme2.xaml" />
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Application.Resources>

Merged resource dictionaries come in useful when:

• providing different themes for the application (like in the sample below)
• providing a new style/template for existing control
• providing a style/template for a custom control

Run the sample online

Source code below: