在原图上添加斜线

- (UIImage *)drawLineWithFile:(NSString *)file {

    UIImage *sourceImage = [UIImage imageWithContentsOfFile:file];

    CGSize imageSize; //画的背景 大小

    imageSize = [sourceImage size];

    UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0.0);

    [sourceImage drawAtPoint:CGPointMake(0, 0)];

    //获得 图形上下文

    CGContextRef context=UIGraphicsGetCurrentContext();

    CGContextDrawPath(context, kCGPathStroke);

    CGFloat space = 6;

    CGPoint aPoints[2];//坐标点

    aPoints[0] =CGPointMake(space,space);//坐标1

    aPoints[1] =CGPointMake(imageSize.width-space,imageSize.height-space);//坐标2

    //CGContextAddLines(CGContextRef c, const CGPoint points[],size_t count)

    //points[]坐标数组，和count大小

    CGContextSetRGBStrokeColor(context, 1, 1, 1, 1);

    CGContextSetLineWidth(context, 1.8);

    CGContextAddLines(context, aPoints, 2);//添加线

    CGContextDrawPath(context,kCGPathStroke);//根据坐标绘制路径

    UIImage *newImage=UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return newImage;

}