private void drag_lbl_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
drag_via_me.AddHandler(Label.MouseEnterEvent, new MouseEventHandler(mouse_enter));
drag_target.AddHandler(Label.MouseEnterEvent, new MouseEventHandler(mouse_enter));
drag_canvas.AddHandler(Canvas.MouseMoveEvent, new MouseEventHandler(mouse_move));
dragPoint = e.GetPosition(drag_lbl);
}