Question

I am performing a drag drop between WPF ListBoxes and I would like to be able to insert into the collection at the position it is dropped rather than the end of the list.

Does anyone know of a solution that is similar to the WinForms ListBox IndexFromPoint function?

Answer 1

I ended up getting this work by using a combination of DragDropEvent.GetPosition, VisualTreeHelper.GetDescendantBounds and Rect.Contains. Here’s what I came up with:

int index = -1;
for (int i = 0; i < collection.Count; i++)
{
   var lbi = listBox.ItemContainerGenerator.ContainerFromIndex(i) as ListBoxItem;
   if (lbi == null) continue;
   if (IsMouseOverTarget(lbi, e.GetPosition((IInputElement)lbi)))
   {
       index = i;
       break;
   }
}

The code resides in the ListBox Drop event. The e object is the DragEventArgs object passed into the Drop event.

The implementation for IsMouseOverTarget is:

private static bool IsMouseOverTarget(Visual target, Point point)
{
    var bounds = VisualTreeHelper.GetDescendantBounds(target);
    return bounds.Contains(point);
}