How to move Content Control DataTemplate to Dictionary Resources XML

I've been given a great example of how to apply a dynamic style within a Conten Control.

I know my XA开发者_如何学JAVAML for each style is going to get really big, I'd like to split the DataTemplate off to separate XAML files (I guess ResourceDictionary's). I just can't seem to get it to work.

<ContentControl Content="{Binding MyViewModel}"> 

<ContentControl.Resources> 
    <DataTemplate x:Key="DefaultTemplate"> 
        <TextBlock Text="DefaultTemplate" /> 
    </DataTemplate> 

    <DataTemplate x:Key="TemplateA"> 
        <TextBlock Text="Template A" /> 
    </DataTemplate>  

    <DataTemplate x:Key="TemplateB"> 
        <TextBlock Text="Template B" /> 
    </DataTemplate> 
</ContentControl.Resources> 

 <ContentControl.Style> 
     <Style TargetType="{x:Type ContentControl}"> 
         <Setter Property="ContentTemplate" Value="{StaticResource DefaultTemplate}" /> 
         <Style.Triggers> 
             <DataTrigger Binding="{Binding SelectedView}" Value="ViewA"> 
                 <Setter Property="ContentTemplate" Value="{StaticResource TemplateA}" /> 
             </DataTrigger> 
             <DataTrigger Binding="{Binding SelectedView}" Value="ViewB"> 
                 <Setter Property="ContentTemplate" Value="{StaticResource TemplateB}" /> 
             </DataTrigger> 
         </Style.Triggers> 
     </Style> 
 </ContentControl.Style> 

As an example, I want this template:

    <DataTemplate x:Key="TemplateB"> 
        <TextBlock Text="Template B" /> 
    </DataTemplate>  

to reside in a different XAML file (lets call it Test.xaml).

I've tried creating a ResourceDictionary file and referencing the Key in the DataTemplate, but obviously it couldn't find the key because it resides in a different XAML file, so I've tried to implement a Merged ResourceDictionary but VS2010 throws errors - e.g.

Test.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

<DataTemplate x:Key="TemplateB">
    <TextBlock Text="Template B" />
</DataTemplate>

with:

<Window.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="Test.xaml"/>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Window.Resources>

But then I get an error "Resources Property has already been set".

What am I doing wrong?

Ben