Question

I’m dipping my toe in the WPF custom control library pool for the first time. I created a project in a separate solution for my custom control which just derives from Control.

In the target App where I want to use the custom control, it works but doesn’t seem to be able to access the default style unless I specifically add a reference in the App.xaml file. I’ve added the xmlns property so the control itself is available. I’m hoping I’m missing some setting that makes the control more self-contained. So in my target WPF app everything works (function and style) if I add the line shown after the comment in App.xaml:

    <Application.Resources>
     <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="MyStandardStuff.xaml" />
            <!-- How do I avoid having everyone who uses the control having to add the following line?-->
            <ResourceDictionary Source="/MyNewControl;component/Themes/Generic.xaml" />
        </ResourceDictionary.MergedDictionaries>
     </ResourceDictionary>
</Application.Resources>

Given that my custom control library has a Themes folder with a Generic.xaml file containing a style of this form:

<Style TargetType="{x:Type local:MyNewControl}">
 <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type local:MyNewControl}">
  ...

Is there some way to make it work without adding the explicit reference in App.xaml?

EDIT

Here’s the ThemeInfo attribute that was created with the project.

[assembly: ThemeInfo(
ResourceDictionaryLocation.None, //where theme specific resource dictionaries are located
//(used if a resource is not found in the page, 
// or application resource dictionaries)
ResourceDictionaryLocation.SourceAssembly //where the generic resource dictionary is located
//(used if a resource is not found in the page, 
// app, or any theme specific resource dictionaries)
)]

Specifics on the Answer

I’m not sure this question will come up again because it turns out I did something stupid, but in case it does… I created the WPF Custom Control Library using the VS template. Then I copied and pasted my control class over the the default class that Visual studio created. What I didn’t notice is that VS created a static constructor that was doing something very important. This was pointed out in a comment to the answer below. The static constructor should look like this

    static MyNewControl()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(MyNewControl),
            new FrameworkPropertyMetadata(typeof(MyNewControl)));
    }

Once this was in place I could remove the code I added to the target’s resource dictionary.

Answer 1

I would make sure that the xaml file in your control assembly is marked as Page and also make sure that you have the ThemeInfo attribute in the assemblyinfo.cs for your control assembly.