+ (AFHTTPSessionManager *)sharedHTTPSession{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        manager = [AFHTTPSessionManager manager];
        manager.requestSerializer.timeoutInterval = 30;
        [manager.requestSerializer  setValue:@"XMLHttpRequest" forHTTPHeaderField:@"X-Requested-With"];
    });
    return manager;
    }

    + (AFURLSessionManager *)sharedURLSession{
    static dispatch_once_t onceToken2;
    dispatch_once(&onceToken2, ^{
        urlsession = [[AFURLSessionManager alloc] initWithSessionConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];
    });
    return urlsession;
    }