iOS-UIGraphics将两个图片合并成一张

原理：

    UIImage *upImg = [UIImage imageNamed:@"mv_01"];
    UIImage *downImg = [UIImage imageNamed:@"mv_02"];
    CGFloat width = 320.f;
    CGFloat height = 480.f;
    UIGraphicsBeginImageContext(CGSizeMake(width, height));//展开画布，自定义尺寸
    [upImg drawInRect:CGRectMake(0, 0, width, height/2)];
    [downImg drawInRect:CGRectMake(0, height/2, width, height/2)];//根据需要定义子图片的位置
    UIImage *resultImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();//关闭画布
    NSString *path = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
    NSString *filePath = [path stringByAppendingPathComponent:@"result.png"];
    [UIImagePNGRepresentation(resultImage) writeToFile:filePath atomically:YES];//保存图片到沙盒
    
    NSLog(@"%@", filePath);