Bezier路径不起作用 - 目标C

Question

我想画一条Bezier路径。它只是不工作。我的代码如下：

UIBezierPath * path = [[UIBezierPath alloc] init];
[[UIColor blackColor] setStroke];
[path setLineWidth:2];
[path moveToPoint:CGPointMake(0, 0)];
[path addLineToPoint:CGPointMake(50,50)];
[path stroke];
[path closePath];

我如何得到它？