图片上画虚线

UIImageView *imageView1 = [[UIImageView alloc]initWithFrame:CGRectMake(0, 100, 320, 20)];      [self.view addSubview:imageView1];                    UIGraphicsBeginImageContext(imageView1.frame.size);   //开始画线      [imageView1.image drawInRect:CGRectMake(0, 0, imageView1.frame.size.width, imageView1.frame.size.height)];      CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);  //设置线条终点形状                       CGFloat lengths[] = {10,5};     CGContextRef line = UIGraphicsGetCurrentContext();      CGContextSetStrokeColorWithColor(line, [UIColor redColor].CGColor);            CGContextSetLineDash(line, 0, lengths, 2);  //画虚线      CGContextMoveToPoint(line, 0.0, 20.0);    //开始画线      CGContextAddLineToPoint(line, 310.0, 20.0);      CGContextStrokePath(line);             imageView1.image = UIGraphicsGetImageFromCurrentImageContext();