Flutter TypeError（类型“List<dynamic>”不是类型“Map<String, dynamic>

Question

我正在使用 Flutter News 模板创建 Flutter 应用程序，当我尝试检索特定类别的提要时，我不断收到此错误：

_TypeError (type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>' in type cast)

。

当我尝试使用应用程序 UI 中的选项卡切换类别时，我确实从端点获取了包含完整 JSON 的日志。我确实需要完整的 JSON，而不是其中的一部分，以便我可以提取应用程序 UI 所需的所有信息。

我添加了一些日志以更好地理解问题。我也尝试在

as Map<String, dynamic>

调用后添加

json()

，但没有帮助。

相关代码：

Future<FeedResponse> getFeed({
    Category? category,
    int? limit,
    int? offset,
  }) async {
    final uri =
        Uri.parse('https://myappurl.com/wp-json/wp/v2/posts?categories=28');
    final response = await _httpClient.get(
      uri,
      // headers: await _getRequestHeaders(),
    );

    if (response.body is List<dynamic>) {
      log('MyLog: Received a list of posts');
    } else {
      log('MyLog: Unexpected response format:');
    }

    final body = response.json(); //This line throws the error

    if (response.statusCode != HttpStatus.ok) {
      throw MyappApiRequestFailure(
        body: body,
        statusCode: response.statusCode,
      );
    }

    return FeedResponse.fromJson(body);
  }

extension on http.Response {
  Map<String, dynamic> json() {
    try {
      final decodedBody = utf8.decode(bodyBytes);
      // log('MyLog decoded ${jsonDecode(decodedBody)}');
      return jsonDecode(decodedBody) as Map<String, dynamic>; //this line is also marked in the error
    } catch (error, stackTrace) {
      Error.throwWithStackTrace(
        MyappApiMalformedResponse(error: error),
        stackTrace,
      );
    }
  }
}

我在调试控制台中遇到的错误：

GetFeedFailure (GetFeedFailure(Instance of 'MyappApiMalformedResponse'))
#0      _extension#0.json (package:myapp_api/src/client/myapp_api_client.dart:370:38)
#1      MyappApiClient.getFeed (package:myapp_api/src/client/myapp_api_client.dart:176:19)
myapp_api_client.dart:176
<asynchronous suspension>
#2      NewsRepository.getFeed (package:news_repository/src/news_repository.dart:76:14)
news_repository.dart:76
<asynchronous suspension>
#3      FeedBloc._updateFeed (package:myapp/feed/bloc/feed_bloc.dart:54:24)
feed_bloc.dart:54
<asynchronous suspension>
#4      Bloc.on.<anonymous closure>.handleEvent (package:bloc/src/bloc.dart:229:13) bloc.dart:229
<asynchronous suspension>

Answer 1

您遇到的错误是因为您收到的响应正文是

List<dynamic>

（帖子数组）而不是

Map<String, dynamic>

。
您的代码尝试将响应转换为 Map 而不是 List，这会导致类型错误。

尝试使用此代码：

Future<List<FeedResponse>> getFeed({
  Category? category,
  int? limit,
  int? offset,
}) async {
  final uri =
      Uri.parse('https://myappurl.com/wp-json/wp/v2/posts?categories=28');
  final response = await _httpClient.get(
    uri,
    // headers: await _getRequestHeaders(),
  );

  if (response.statusCode != HttpStatus.ok) {
    throw MyappApiRequestFailure(
      body: response.body,
      statusCode: response.statusCode,
    );
  }

  final body = response.json(); // Decoding the response

  // Here, handle the case where the response is a list of posts
  if (body is List<dynamic>) {
    log('MyLog: Received a list of posts');
    return body.map((post) => FeedResponse.fromJson(post as Map<String, dynamic>)).toList();
  } else {
    log('MyLog: Unexpected response format: $body');
    throw MyappApiMalformedResponse(error: 'Unexpected response format');
  }
}

extension on http.Response {
  List<dynamic> json() {
    try {
      final decodedBody = utf8.decode(bodyBytes);
      return jsonDecode(decodedBody) as List<dynamic>; // Decoding as a List<dynamic>
    } catch (error, stackTrace) {
      Error.throwWithStackTrace(
        MyappApiMalformedResponse(error: error),
        stackTrace,
      );
    }
  }
}

注意：-希望上面的代码能够正常工作，因为我不确定您在这个 API 中得到了什么。请确保您获取的响应是List。