Xaml Design View can't find Background Brush - wpf

Question

in order to clean up my code, I'm trying to split my app.xaml into seperate resource dictionaries. This works at runtime, but not at design time:
snipped in app.xaml
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/;component/Theme/Colors.xaml" />
<ResourceDictionary Source="/;component/Theme/Styles.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
Colors.xaml
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<SolidColorBrush x:Key="backgroundBrush" Color="Gold"/>
</ResourceDictionary>
Styles.xaml
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Style TargetType="StatusBar">
<Setter Property="Background" Value="{StaticResource backgroundBrush}" />
</Style>
</ResourceDictionary>
Snipped of MainWindow.xaml
<Window x:Class="test.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="test" Width="800" Height="600" >
<StatusBar Name="statusBar" DockPanel.Dock="Bottom">
<StatusBarItem Content="{Binding statusMessage}" />
</StatusBar>
DesignView gives the error:
Error 8 '{DependencyProperty.UnsetValue}' is not a valid value for property 'Background'. C:\Daten\DotNet\test\test\MainWindow.xaml 123
If I put backgroundBrush directly into app.xaml like so:
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/;component/Theme/Colors.xaml" />
<ResourceDictionary Source="/;component/Theme/Styles.xaml" />
<ResourceDictionary>
<SolidColorBrush x:Key="backgroundBrush" Color="Gold"/>
</ResourceDictionary>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
DesignView has no problems.
So is there a way to tell DesignView where to find backgroundBrush, if this brush is placed into a seperate resource dictionary?

Answer 1

Thats the problem with StaticResource isnt it. It needs the resource key resolved explicitly using shared \ merged \ direct resource dictionaries hierarchically up.
There are two options...
merge Colors.xaml dictionary in Styles.xaml
OR
in Styles.xaml refer the bursh using DynamicResource.

Answer 2

In case Resources are in different assemblies than that where MainWindow resides and the one dictionary is refering to the other dictionary. In that case reference is not resolved. This bug is already reported at Microsoft site in case your target framework is 4.0. However they have provided a workaround for it. Simply add the empty style in your Resource dictionaries and it will work fine like this -
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/;component/Theme/Colors.xaml" />
<ResourceDictionary Source="/;component/Theme/Styles.xaml" />
</ResourceDictionary.MergedDictionaries>
<Style TargetType="{x:Type Window}"/>
</ResourceDictionary>
</Application.Resources>
For further refernce please look at this link - https://connect.microsoft.com/VisualStudio/feedback/details/555322/global-wpf-styles-are-not-shown-when-using-2-levels-of-references#details

Answer 3

Try
{StaticResource ApplicationPageBackgroundThemeBrush}
for your status bar background value