iOS：后台返回json数据格式错误无法解析

NSString *resultString = [self responseString];//self为网络请求操作类（completedOperation）
NSData *data = [[resultString stringByReplacingOccurrencesOfString:@"\r\n" withString:@"\\r\\n"] dataUsingEncoding:NSUTF8StringEncoding];
NSError *error = nil;
result = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:&error];