在后台模式下通过AFHTTPSessionManager进行迭代

Question

我正在使用AFHTTPSessionManager多次从API检索信息。当它不在后台模式下时，它可以正常工作，尽管一旦关闭应用程序，AFHTTPSessionManager调用似乎就无法正常工作，它将阻止。

-(void)requestGET:(NSString *)strURL xml:(BOOL)xml Token:(NSString *)token success:(void (^)(NSDictionary *responseObject))success failure:(void (^)(NSError *error))failure {

    BOOL isNetworkAvailable = [self checkNetConnection];

    if (!isNetworkAvailable) {
        NSLog(@"No connection");
        [self showAlert:@"Please check your internet connection"];
        return;
    }else{

        AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
        [manager.requestSerializer setValue:[NSString stringWithFormat:@"Bearer %@",token] forHTTPHeaderField:@"Authorization"];

        if(xml){
            // Content xml
            manager.responseSerializer = [AFHTTPResponseSerializer new];
            manager.responseSerializer.acceptableContentTypes = [NSSet setWithObjects:@"application/vnd.garmin.tcx+xml", nil];
        }else{
            // Content json
            manager.responseSerializer.acceptableContentTypes = [NSSet setWithObjects:@"application/json", nil];
        }

        [manager GET:strURL parameters:nil progress:nil success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
            if([responseObject isKindOfClass:[NSDictionary class]]) {
                // Return json
                if(success) {
                    success(responseObject);
                }
            }else{
                // Return xml to nsdictionary
                if(success){
                    NSString* responseStr = [[NSString alloc] initWithData:responseObject encoding:NSUTF8StringEncoding];
                    NSDictionary * XMLDictionary = [XMLReader dictionaryForXMLString:responseStr error:nil];
                    success(XMLDictionary);
                }
            }
        } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
            NSLog(@"%@", error);
            if(failure) {
                failure(error);
            }
        }];
    }
}

下面多次调用上述方法，以从API抓取数据并将其抽出。

-(void)getFitbitURL{

    // Create group
    dispatch_group_t group = dispatch_group_create();

    // Retrieve array
    NSMutableArray *URLS = [self generateURLS];
    for (NSMutableArray *entity in URLS){

        NSString *url = entity[0];

        // Enter group
        dispatch_group_enter(group);

        NSString *token = [FitbitAuthHandler getToken];
        FitbitAPIManager *manager = [FitbitAPIManager sharedManager];

        // Get URL
        [manager requestGET:url xml:0 Token:token success:^(NSDictionary *responseObject) {

            // Do stuff with output
            printf("%s",[[responseObject description]UTF8String]);

            // Leave group
            dispatch_group_leave(group);

        } failure:^(NSError *error) {
            NSLog("%@",error);

            // Leave group
            dispatch_group_leave(group);
        }];
    }

    // Wait for all of group to complete 
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
      NSLog(@"Complete");
    });
}

我试图在互联网上研究如何执行此操作，但是我的所有想法都失败了，当应用程序关闭时，我的applicationDidEnterBackground方法可以正常运行，但其他所有功能（例如url请求）均无法正常运行。任何建议，将不胜感激