Ios 无法在AFNetworking中获取下载进度

我正在尝试使用以下代码段使用AFNetworking 2.0下载一个文件

AFHTTPRequestSerializer *serialize = [AFHTTPRequestSerializer new];
[serialize setAuthorizationHeaderFieldWithUsername...// set the auth header with username and password
serialize.timeoutInterval = 200;
NSError *error = nil;
NSMutableURLRequest *request = [serialize requestWithMethod:@"GET" URLString:url parameters:nil error:&error];
AFHTTPSessionManager *session = [AFHTTPSessionManager manager];
NSProgress *progress = nil;

NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithRequest:request progress:&progress destination:^NSURL *(NSURL *targetPath, NSURLResponse *response) {
    NSLog(@"success….”);
    NSURL *url = [NSURL new];
    return url;
} completionHandler:^(NSURLResponse *response, NSURL *filePath, NSError *error) {
    NSLog(@"error: %@", error.localizedDescription);
    }];

[progress addObserver:self forKeyPath:@"fractionCompleted" options:NSKeyValueObservingOptionNew context:NULL];
[downloadTask resume];
}

//在此处添加观察者以获得进展

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{

dispatch_async(dispatch_get_main_queue(), ^{
    if ([keyPath isEqualToString:@"fractionCompleted"]) {
        NSProgress *progress = (NSProgress *)object;
        NSLog(@"Progress… %f total unit count =%lld , completed unit count =%lld", progress.fractionCompleted , progress.totalUnitCount,progress.completedUnitCount);
    } else {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
});

}

这是来自

observeValueForKeyPath

方法的NSLog

SampleDownload[5833:149756] Progress… 0.000000 total unit count =-1 , completed unit count =0
SampleDownload[5833:149756] Progress… 0.000000 total unit count =-1 , completed unit count =975
SampleDownload[5833:149767] Progress… 0.000000 total unit count =-1 , completed unit count =25149
SampleDownload[5833:149767] Progress… 0.000000 total unit count =-1 , completed unit count =31086
SampleDownload[5833:149767] Progress… 0.000000 total unit count =-1 , completed unit count =53006
SampleDownload[5833:149754] Progress… 0.000000 total unit count =-1 , completed unit count =54377
SampleDownload[5833:149755] Progress… 0.000000 total unit count =-1 , completed unit count =66098
SampleDownload[5833:149768] Progress… 0.000000 total unit count =-1 , completed unit count =93626
SampleDownload[5833:149763] Progress… 0.000000 total unit count =-1 , completed unit count =103805

你们可以看到，我得到的总单位数是-1。因此，我认为

fractionCompleted

为0，无法更新UI。我犯了什么错误

我已将此作为参考。

也有一些类似的讨论发生在这个线程，但我无法找出原因。

编辑

发布响应标题

{
"Access-Control-Allow-Credentials" = true;
"Access-Control-Allow-Headers" = "Accept,Authorization,Cache-Control,Content-Type,DNT,If-Modified-Since,Keep-Alive,Origin,User-Agent,X-Mx-ReqToken,X-Requested-With";
"Access-Control-Allow-Methods" = "GET, POST, PUT, DELETE, OPTIONS";
"Access-Control-Allow-Origin" = "*";
"Cache-Control" = "public, max-age=43200";
Connection = "keep-alive";
"Content-Encoding" = gzip;
"Content-Length" = 1166764;
"Content-Type" = "application/pdf";
Date = "Wed, 17 Dec 2014 12:17:43 GMT";
Etag = “someEtag”;
Expires = "Thu, 18 Dec 2014 00:17:43 GMT";
"Last-Modified" = "Wed, 17 Dec 2014 11:58:31 GMT";
Server = "nginx/1.4.6 (Ubuntu)";
Vary = "Accept-Encoding";
}

---

问题可能是

gzip

的

Content Encoding

，这可能导致

nsurlsessiondownloaddedelegate

方法

didWriteData

返回预期总字节数的-1。在发出请求之前，您可以通过设置

Accept Encoding

尝试禁用

gzip

：

[request setValue:@"" forHTTPHeaderField:@"Accept-Encoding"];

---

检查服务器是否返回

内容长度
@Andy谢谢！用我得到的回复标题更新了问题的详细信息。嗯，我不知道，对我来说一切似乎都是合法的。看到了吗（请记住，在谷歌搜索时，如果在搜索词中包含
-1
，我认为它会排除所有提到数字1的页面，无论是正面还是负面！
-
是谷歌的。）