Editing a DataTemplate with Expression Blend for items that use a DataTemplateSelector

Question

Im my app, I have an ItemsControl element which houses user-drawn shapes. Each specific shape's ViewModel inherits from a base ViewModel. A DataTemplateSelector applies the correct DataTemplate based on the shape's ViewModel type.

in my win xaml:

    <ItemsControl ItemsSource="{Binding MarkupElements}"
                  ItemTemplateSelector="{StaticResource MarkupTemplateSelector}"/>
        <ItemsControl.ItemsPanel>
            <ItemsPanelTemplate>
                <Canvas Panel.ZIndex="1" />
            </ItemsPanelTemplate>
        </ItemsControl.ItemsPanel>
    </ItemsControl>

in a resource dictionary:

    <DataTemplate x:Key="MarkupLineTemplate" DataType="x:Type vm:MarkupLineViewModel">
    <.../>
    </DataTemplate>
    <DataTemplate x:Key="MarkupCircleTemplate" DataType="x:Type vm:MarkupCircleViewModel">
    <.../>
    </DataTemplate>
    <view:MarkupTemplateSelector
    LineTemplate="{StaticResource MarkupLineTemplate}"
    CircleTemplate="{StaticResource MarkupCircleTemplate}"
    x:Key="MarkupTemplateSelector"/>

This works fine, but Expression Blend doesn't let me edit those templates. I can force Blend to apply a specific template, but it then adds a ItemTemplate property to my win.xaml set to the one I chose, overriding the selector.

I'm using the MVVM Light Tookit, and tried adding a few design-time shapes of different types. Blend does show them, but they're no help with accessing the templates.

Is there a way to convince Blend that my derived ViewModels are valid for the DataContext, thus allowing me to edit the templates? Is this even the problem?

Answer 1

In the Resources tab in Expression Blend, you should be able to find the data template (either from a resource dictionary or the current screen). You can then click to edit the template. Does that help?