WPF: How to install thumb behavior in a Canvas?

Question

I would like to have a Canvas that supports the DragDelta event. My first idea of how to do this was to make a ControlTemplate that includes a thumb. But I do not know how to do this correctly. How can I change the XAML below to make it compile, and what's the right way to install the DragDelta event handler?

<UserControl.Resources>
    <ControlTemplate x:Key="Transparent">
        <Rectangle Fill="Transparent"/>
    </ControlTemplate>
    <ControlTemplate x:Key="ThumbCanvas" TargetType="{x:Type Canvas}">
        <Grid>
            <Thumb x:Name="CanvasThumb" Template="{StaticResource Transparent}" DragDelta="CanvasThumb_DragDelta"/>
            <ContentPresenter Content="{TemplateBinding Content}"/>
            <!--error MC3011: Cannot find the static member 'ContentProperty' on the type 'Canvas'.-->
        </Grid>
    </ControlTemplate>
</UserControl.Resources>

Answer 1

Any panel derived control doesn't have a template property, since they have no visible components.

You can use the Thumb control inside the UserControl, like you are doing and just adjust the Height/Width of the UserControl based on the delta of the Thumb. To make this work correctly, you need to get the mouse location relative to the parent of the usercontrol, otherwise it won't work well. ie: e.GetLocation(this.Parent);

You should probably size the height/width on that thumb as well. It's a good idea to set the cursor on it also.