我写了这么个方法用来发送图片。怎么看也没错啊。打印TTURLRequest的日志出来看，显示数据已经发出去了。

可是服务器返回的提示就说图片文件为空，这是为什么呀？

+ (void)doAsynchronousRequestPost:(NSString *)url 
                             File:(NSDictionary *)file
                         Delegate:(id)delegate 
                         WithInfo:(NSDictionary *)info {

    TTURLRequest *request = [self requestPost:url Delegate:delegate];

    request.response = [[[TTURLJSONResponse alloc] init] autorelease];

    if (nil != info) {
        [request setUserInfo:info];
    }

    if (nil != file) {
        NSData *imageData = UIImageJPEGRepresentation([file objectForKey:@"data"], 0.7f);
        [request addFile:imageData mimeType:[file objectForKey:@"type"] fileName:[file objectForKey:@"key"]];
    } else {
        return;
    }

    [request send];

}