WPF UIElement.IsHitTestVisible=false; still returning hits?

Question

I'm deriving a control from FrameworkElement to use as a container for a VisualCollection, as I'm doing a lot of custom rendering using DrawingVisuals (creating a game map).

I've got a couple different instances of my container layered on top of each other, and I only want hit testing to affect the layer currently visible, so I tried doing the obvious, and set .IsHitTestVisible=false, which according to MSDN should prevent any child elements being returned as hit results.

However, I am still getting hits returned on the containers that are set .IsHitTestVisible=false. I've tried everything else I can think of, Collapsed, Hidden, Disabled, 0 Opacity, nothing seems to take it out of the hit testing.

Attainment

The only workaround I've found so far is to actually remove the container control from it's parent collection, so that it's completely out of the VisualTree hierarchy. – Attainment

Answer 1

I think it's a bug. I used Reflector to understand why the HitTest method returns invisible items and I have found that there is no check for visibility.

My solution is to use overload HitTest with filter:

public static HitTestFilterBehavior HitTestFilterInvisible(DependencyObject potentialHitTestTarget)
{
    bool isVisible = false;
    bool isHitTestVisible = false;

    var uiElement = potentialHitTestTarget as UIElement;
    if (uiElement != null)
    {
        isVisible = uiElement.IsVisible;
        if (isVisible)
        {
            isHitTestVisible = uiElement.IsHitTestVisible;
        }
    }
    else
    {
        UIElement3D uiElement3D = potentialHitTestTarget as UIElement3D;
        if (uiElement3D != null)
        {
            isVisible = uiElement3D.IsVisible;
            if (isVisible)
            {
                isHitTestVisible = uiElement3D.IsHitTestVisible;
            }
        }
    }

    if (isVisible)
    {
        return isHitTestVisible ? HitTestFilterBehavior.Continue : HitTestFilterBehavior.ContinueSkipSelf;
    }

    return HitTestFilterBehavior.ContinueSkipSelfAndChildren;
}
...
// usage:

    VisualTreeHelper.HitTest(
        myHitTestReference,
        HitTestFilterInvisible,
        hitTestResult =>
        {
            // code to handle element which is visible to the user and enabled for hit testing.
        },
        new PointHitTestParameters(myHitTestPoint));

I hope it will help you

Futurism

Although I was hoping for a way to make the behavior work as MSDN describes rather than a workaround, this was helpful so I'll mark it as the answer. – Attainment

I am having the same issue with a border that is part of my scrollviewer template... I have a border at the bottom that creates a little "hint" shadow so the user knows the content is scrollable, but the border is blocking mouse events from the content underneath it... I have set IsHitTestVisible="false" on the border but it still gets mouse events. Unfortunately I am not dealing with any code behind files so I can't override the hit test methods... any ideas? – Schwerin