如何修复Dio异步请求中FutureOr<Response<dynamic>>返回null的错误？

问题代码 #

Future<void> clipsAdd(int questionId) async {
  await _authenticatedRequest((options) async {
    final String uri = "$domain/clips/add?questionId=$questionId";
    final response = await dio.post(uri, options: options);

    if (response.statusCode != 200) {
      throw Exception('Failed to process request: ${response.statusCode}');
    }
  });
}

错误信息 #

The body might complete normally, causing 'null' to be returned, but the return type,
'FutureOr<Response>', is a potentially non-nullable type.
Try adding either a return or a throw statement at the end.

错误原因 #

传给_authenticatedRequest的匿名函数，因内部调用dio.post（返回Response<dynamic>），Dart会推断该函数返回类型为Future<Response<dynamic>>。但请求成功（状态码200）时，函数无返回值，在空安全规则下会被视为可能返回null，与非空的推断类型冲突，触发错误。

修复方案 #

方案1：显式指定匿名函数返回类型为Future<void> #

如果不需要使用dio.post的返回结果，直接明确函数无需返回值：

Future<void> clipsAdd(int questionId) async {
  await _authenticatedRequest((BaseOptions options) async {
    final String uri = "$domain/clips/add?questionId=$questionId";
    final response = await dio.post(uri, options: options);

    if (response.statusCode != 200) {
      throw Exception('Failed to process request: ${response.statusCode}');
    }
  } as Future<void> Function(BaseOptions));
}

方案2：成功时返回response #

若需保留返回response的可能性，或仅为满足类型推断要求，在函数末尾添加返回语句：

Future<void> clipsAdd(int questionId) async {
  await _authenticatedRequest((options) async {
    final String uri = "$domain/clips/add?questionId=$questionId";
    final response = await dio.post(uri, options: options);

    if (response.statusCode != 200) {
      throw Exception('Failed to process request: ${response.statusCode}');
    }
    return response; // 添加返回语句，匹配推断的返回类型
  });
}

内容的提问来源于stack exchange，提问作者CodeNewbie