网上找的
CAShapeLayer *dotteShapeLayer = [CAShapeLayer layer];
CGMutablePathRef dotteShapePath = CGPathCreateMutable();
//设置虚线颜色为blackColor
[dotteShapeLayer setStrokeColor:[[UIColor orangeColor] CGColor]];
//设置虚线宽度
dotteShapeLayer.lineWidth = 1.0f ;
//10=线的宽度 5=每条线的间距
NSArray *dotteShapeArr = [[NSArray alloc] initWithObjects:[NSNumber numberWithInt:1],[NSNumber numberWithInt:3], nil];
[dotteShapeLayer setLineDashPattern:dotteShapeArr];
// 50为虚线Y值，和下面的50一起用。
// kScreenWidth为虚线宽度
CGPathMoveToPoint(dotteShapePath, NULL, 0 ,50);
CGPathAddLineToPoint(dotteShapePath, NULL, kScreenWidth, 50);
[dotteShapeLayer setPath:dotteShapePath];
CGPathRelease(dotteShapePath);
//把绘制好的虚线添加上来
[self.layer addSublayer:dotteShapeLayer];
