In WPF setting e.Effects in DragOver doesn't work - why?

Question

I am new in WPF. I am implementing Drag&Drop in a TreeView and my DragOver event handler does not work.

<Style TargetType="TreeViewItem">
    <!-- ... -->
    <EventSetter Event="DragOver" Handler="item_DragOver" />
</Style>

void item_DragOver(object sender, DragEventArgs e)
{
    if (!e.Data.GetDataPresent("someFormat") || e.Source == sender)
        e.Effects = DragDropEffects.None;                
    else if (e.KeyStates == DragDropKeyStates.ControlKey)
        e.Effects = DragDropEffects.Copy;
    else
        e.Effects = DragDropEffects.Move;

    e.Handled = true;
}

When the program runs when dragging over some tree items it shows always a "move" drag icon, even if I press the Ctrl key. I suppose some default event handler overrides my e.Effects, but I do not know where I can search for it.

Any Idea?

Answer 1

I found it, to check if ctrl-key is pressed the right way is:

if ((e.KeyStates & DragDropKeyStates.ControlKey) == DragDropKeyStates.ControlKey)