Code

private void fc_BoxModified(object sender, BoxMouseArgs e)
{
	Box box = e.Box;

	// lock the dropped box, so that GetBoxAt ignore it
	box.Locked = true;

	// find the box below the mouse cursor position
	Box newParent = fc.GetBoxAt(new PointF(e.X, e.Y));
	if (newParent != null)
	{
		if  (box.IncomingArrows.Count > 0)
			box.IncomingArrows[0].Origin = newParent;
		else
			fc.CreateArrow(newParent, box);

		TreeLayout tl = new TreeLayout(newParent);
		tl.KeepRootPosition = true;
		tl.Arrange(fc);
	}

	box.Locked = false;
}