I found this:
LineConnector line = new LineConnector(new PointF(100, 100), new PointF(400, 100));
//By setting false AllowMoveY for both HeadEndPoint and TailEndPoint it will draw a straight line.
line.HeadEndPoint.AllowMoveY = false;
line.TailEndPoint.AllowMoveY = false;
But I want that a line (every line that I use) ALWAYS has allowmoveY disabled by default. How can I do it?