数据返回的一个字符串类型的 不是json类型

AFHTTPSessionManager *manager =  [AFHTTPSessionManager manager];      manager.responseSerializer = [AFHTTPResponseSerializer serializer];     NSString *str = [NSString stringWithFormat:HuXingBaoMingChoice,_appdelegate.uuid,_detaiLID];          [manager GET:str parameters:nil progress:^(NSProgress * _Nonnull downloadProgress) {              } success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {         NSString *string = [[NSString alloc] initWithData:responseObject encoding:NSUTF8StringEncoding];         self.textContent  = [string copy];            } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {          }];