UIImageView *imageView1 = [[UIImageView alloc]initWithFrame:CGRectMake(0, 200, 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
    
const CGFloat lengths[] = {5,3};
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();