Can't find ResourceDictionary in Add New Item Window

Add the following line to Project.csproj

    <ProjectTypeGuids>{60dc8134-eba5-43b8-bcc9-bb4bc16c2548};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>

It should be a child of the <PropertyGroup> tag, like so:

    <Project>
      <PropertyGroup>
        ....
        <ProjectTypeGuids>{guids};{go};{here}</ProjectTypeGuids>
        ...
      </PropertyGroup>
    ...
    </Project>

This post does a good job of explaining why this works.

First of all, I hope you realize this shouldn't stop you since you can easily add any file you want to a project, either from your file system or by copying it from another project. The Add New Item window is just for convenience.

Secondly, when you added the new project to your solution, which project template did you choose? The project template determines the initial set of referenced assemblies that project has. A WPF project makes references to the WPF libraries (WindowsBase, PresentationCore, etc.).

Visual Studio uses your referenced assemblies to generate the possible items you see in the Add New Items dialog.

So I'm assuming you added some other type of project, such as a basic Class Library. You could manually add the references to the WPF assemblies using the Add Reference dialog. Or you could re-create the project as a WPF Custom Control Library.