Question

I am developing a user control and use it inside an ElementHost. I define the resource dictionary as follows:

<UserControl.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="/Themes/Classic.xaml"/>
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary> 
    </UserControl.Resources>

In my VS explorer, I have this

Project (the user control library)
  |_ Themes
       |__ Generic.xaml  (Build Action = Page)
       |__ Classic.xaml  (Build Action = Page)

There’s no compilation error and the VS designer seems to pick up the resources defined in Classic.xaml

However, it crashes at runtime with the following exception:

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. —> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. —> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. —> System.Windows.Markup.XamlParseException: ‘Set property ‘System.Windows.ResourceDictionary.Source’ threw an exception.’ Line number ’16’ and line position ’18’. —> System.IO.IOException: Cannot locate resource ‘themes/classic.xaml’.

What’s going on?

Answer 1

I ended up having to use the syntax that includes the assembly name… don’t ask me why

<UserControl.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="/assemblyname;component/Themes/Classic.xaml"/>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary> 
</UserControl.Resources>