- (void)drawLineByImageView:(UIImageView *)imageView {
    UIGraphicsBeginImageContext(imageView.frame.size);   //开始画线 划线的frame
    [imageView.image drawInRect:CGRectMake(0, 0, imageView.frame.size.width, imageView.frame.size.height)];
    //设置线条终点形状
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
    
    CGContextRef line = UIGraphicsGetCurrentContext();
    // 设置颜色
    CGContextSetStrokeColorWithColor(line, [UIColor darkGrayColor].CGColor);
    
    
    CGFloat lengths[] = {5,2};//先画4个点再画2个点
    CGContextSetLineDash(line,0, lengths,2);//注意2(count)的值等于lengths数组的长度
    
    CGContextMoveToPoint(line, 0.0, 2.0);    //开始画线
    CGContextAddLineToPoint(line,imageView.frame.size.width,2.0);

    CGContextStrokePath(line);
    // UIGraphicsGetImageFromCurrentImageContext()返回的就是image
    UIImage *image =   UIGraphicsGetImageFromCurrentImageContext();
    imageView.image = image;
}