StaticResource causes XamlParseException when loaded from another assembly

Question

I created a test solutions with 2 WPF assemblies.

In "AssemblyTest", I have a simple default window, "OtherWindow", that does nothing. In "StartingAssembly, I have also have a simple default window, "MainWindow" that initializes and Show() the OtherWindow from AssemblyTest.

All references are correct and in this case everything works fine; both windows show up correctly the way they are expected to.

using AssemblyTest;

namespace StartingAssembly
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        OtherWindow window = new OtherWindow();
        public MainWindow()
        {
            InitializeComponent();
            window.Show();
        }
    }
}

However, an issue occurs when I change "OtherWindow" to use a StaticResource.

This works correctly:

<Window x:Class="AssemblyTest.OtherWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="OtherWindow" Height="350" Width="525" Background="Blue">
    <Grid>

    </Grid>
</Window>

However, this causes a XamlParseException:

<Window x:Class="AssemblyTest.OtherWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="OtherWindow" Height="350" Width="525" Background="{StaticResource mainLoginBackground}">
    <Grid>

    </Grid>
</Window>

The resource is located at CommonResourceDictionary.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:sys="clr-namespace:System;assembly=mscorlib">

    <RadialGradientBrush x:Key="mainLoginBackground" GradientOrigin="0.5,0.5" Center="0.5,0.5" RadiusX="1" RadiusY="1">
        <GradientStopCollection>
            <GradientStop Color="#ff0f75ba" Offset="0" />
            <GradientStop Color="#ff033657" Offset="1" />
        </GradientStopCollection>
    </RadialGradientBrush>
</ResourceDictionary>

This is App.xaml from AssemblyTest

<Application x:Class="AssemblyTest.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             StartupUri="OtherWindow.xaml">
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="/Resources/CommonResourceDictionary.xaml" />
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>
</Application>

Finally, Here is the error:

I wrote this question using an example that is as basic as possible, so that I can apply to a bigger project. If you can help me figure what is missing, I will be able to use this solution on a bigger project I'm working with. In addition, I have searched StackOverflow for similar questions, but none close to this specific issue.

Answer 1

Since the ResourceDictionary is defined in another assembly you should use a pack URI to reference it:

<ResourceDictionary Source="pack://application:,,,/AssemblyTest;component/Resources/CommonResourceDictionary.xaml" />

You can read more about this here: https://msdn.microsoft.com/en-us/library/aa970069(v=vs.110).aspx