AFNetworking 2.0 AFHTTPRequestOperationManager CachePolicy不工作

我正在尝试使用If Modified Since标头向服务器发出GET请求,以避免加载相同的内容。当我发出请求时,我知道服务器正在发回一个304,表明内容没有更改,但NSURLCache或AFNetworking正在响应一个200,其中包含缓存的内容。为了防止这种情况,我将请求序列化程序的缓存策略设置为NSURLRequestReloadIgnoringLocalCacheData,但这并不能解决问题。

- (void)getConfig {

    //Retrive the timeStamp at which the config was last updated
    NSDate *timeStamp = [[NSUserDefaults standardUserDefaults] objectForKey:@"lastGetConfigDate"];

    //Get the rfc1123 representation of the timeStamp
    NSString *dateString = [timeStamp rfc1123String];

    //If we're not force loading the data then include the time stamp in the If-modified-Since header
    [self.requestSerializer setValue:[NSString stringWithFormat:@"%@", dateString] forHTTPHeaderField:@"If-Modified-Since"];

    //Setting cachePolicy to ignore cache data to prevent the cached response
    [self.requestSerializer setCachePolicy:NSURLRequestReloadIgnoringLocalCacheData];

    //GET REQUEST to /api/config
    [self GET:@"/api/config" parameters:nil success: ^(AFHTTPRequestOperation *operation, id responseObject) {
        NSDictionary *jsonDict = (NSDictionary *)responseObject;

        DDLogInfo(@"Config: 200");

        //If the config data was successfully loaded then set the lastGetConfigDate time stamp in the nsuserdefaults to send in the next call with the if-modified-since header
        if (success) {
            [[NSUserDefaults standardUserDefaults] setObject:[NSDate date] forKey:@"lastGetConfigDate"];
        }

    } failure: ^(AFHTTPRequestOperation *operation, NSError *error) { ....