WPF Resource Dictionary using code behind file can’t be found

Question

When I include an assembly containing a ResourceDictionary using the following pack syntax:

"pack://application:,,,/WpfCore;component/ResourceDictionaries/ThemedControls.xaml"

It works as expected, but as soon as I add a code behind file to the XAML of the ResourceDictionary, the following error is thrown: “An error occurred while finding the resource dictionary”

The code behind is added to the XAML in the usual way:

< ResourceDictionary x:Class="com.mycompany.WpfCore.ResourceDictionaries.ThemedControls"
                    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
                    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006">
</ResourceDictionary>

and looks like this:

namespace com.mycompany.WpfCore.ResourceDictionaries
{
    public partial class ThemedControls : ResourceDictionary
    {
        public ThemedControls ()
        {
            InitializeComponent();
        }
    }
}

Intuition tells me this is a namespace problem, but all the variations I've tried fail. What am I doing wrong or is this a limitation of WPF ResourceDictionaries?

Edit:

Seems the question detail was called out and found to be wanting.

The initial example had the namespace simplified. The default namespace for the WpfCore project is com.mycompany.WpfCore which I have now added into the code examples above.

The ThemedControls.xaml and ThemedControls.xaml.cs files are located in a subfolder called ResourceDictionaries within the WpfCore project folder. The resulting assembly is used as a referenced assembly in another solution and this is where the Pack URI is being used.

Edit 2:

After playing around with the build action for the xaml files (changing from page to resource and back again) things started working. Marking Sheridan's answer as correct.

Answer 1

I don't think that you have declared your ResourceDictionary quite correctly... the application name really should be in the namespace. This should work... at least it works for me:

<ResourceDictionary 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    x:Class="WpfCore.ResourceDictionaries.ThemedControls">
</ResourceDictionary>

Code behind:

namespace WpfCore.ResourceDictionaries
{
    public partial class ThemedControls : ResourceDictionary
    {
        public ThemedControls()
        {
            InitializeComponent();
        }
    }
}