Question

Suppose I wanted to do this, so I can find the current position of the mouse relative to a Visual, without needing access to a specific mouse event:

public static Point GetMousePosition(this Visual relativeTo)
{
    return relativeTo.PointFromScreen(GetMousePositionOnScreen());
}

Sometimes (usually when I’ve just switched between two tab controls) PointFromScreen throws an InvalidOperationException with the message This Visual is not connected to a PresentationSource.

On looking at the properties available on Visual I can’t see any relating to a PresentationSource.

Given a Visual, how can I tell if it is going to throw that exception when I call PointFromScreen on it?

Answer 1

There’s a static method PresentationSource.FromVisual which:

Returns the source in which a provided Visual is presented.

I know this doesn’t solve the underlying problem, but you could check that the Visual is connected to a PresentationSource before calling PointFromScreen. It would prevent the exception, but you’d need to do some more investigation as to why it wasn’t connected in the first place.