Question

I’ve created the following control:

<UserControl x:Class="FooBar.AnnotationControl"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Height="400" Width="500" >
    <ScrollViewer Height="400" Width="500">
        <Canvas Height="400" Width="500" Name="ctlCanvas" MouseLeftButtonDown="MouseLeftButtonDownHandler" >
            <Canvas.RenderTransform>
                <ScaleTransform x:Name="ZoomTransform" />
            </Canvas.RenderTransform>
        </Canvas>
    </ScrollViewer>
</UserControl>

namespace FooBar
{

    public partial class AnnotationControl : UserControl
    {
        public AnnotationControl()
        {
            InitializeComponent();

        }

        private void MouseLeftButtonDownHandler( object sender, MouseButtonEventArgs args)
        {
           //Do Something
        }

    }

}

when I click the canvas, I don’t hit breakpoints in the MouseLeftButtonDownHandler. I even attach this handler to the ScrollViewer and get the same result. Any idea what’s going on here?

Answer 1

The default background for a Canvas is Transparent, which allows hit tests to pass through it. To make your Canvas register for HitTests, give it a Background Color.

<Canvas Background="White" ... />