现在做的一个项目需要上传图片，我就使用了AFNetWorking中的multipartFormRequestWithMethod方法，由于可能要一次上传多张图片，就按照如下代码来写的：

UIImage *image1 = [UIImage imageNamed:@"about_app"];
UIImage *image2 = [UIImage imageNamed:@"alter"];
NSArray *array = @[image1,image2];
__block int i = 0;
NSMutableURLRequest *request = [[AFNetWorkSingleton shareInstance] multipartFormRequestWithMethod:@"POST" path:@"Mindex/getimg" parameters:nil constructingBodyWithBlock:^(id<AFMultipartFormData>formData){
    for(UIImage *eachImage in array)
    {
        NSData *imageData = UIImageJPEGRepresentation(eachImage,0.5);
        [formData appendPartWithFileData:imageData name:[NSString stringWithFormat:@"file%d",i ] fileName:[NSString stringWithFormat:@"abc%d.jpg",i ] mimeType:@"image/jpeg"];
        i++;
    }
}];

AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject){}

可是这样写不能成功提交到服务器, 但是将multipartFormRequestWithMethod方法中的for循环替换成下面这样的就成功上传了，这是为什么？我哪里写错了吗？

    [formData appendPartWithFileData:UIImageJPEGRepresentation([array objectAtIndex:0], 0.5) name:@"image1" fileName:@"image1.jpg" mimeType:@"image/jpeg"];
    [formData appendPartWithFileData:UIImageJPEGRepresentation([array objectAtIndex:1], 0.5) name:@"image2" fileName:@"image2.jpg" mimeType:@"image/jpeg"];