Flutter调用API转换List<dynamic>报错，需获取ProblemWithCommentModel列表

问题分析 #

错误根源在于你请求的https://localhost:7050/api/Problem/1接口返回的是单个Problem对象（_JsonMap类型），但你在代码里强行将其转换为List<dynamic>，导致类型不匹配。之前用List处理有效是因为当时请求的是列表接口（如/api/Problem不带ID），但本次是带ID的详情接口，返回的是单个实体。

修复方案 #

场景1：获取单个对象并包装为列表 #

如果你的业务确实需要将单个接口返回的对象转为ProblemWithCommentModel类型的列表，修改getProblem方法如下：

Future<void> getProblem() async {
  final response = await dio.get('https://localhost:7050/api/Problem/1',
      options: Options(
        headers: {"content-type": "application/json"},
      ));
  // 先将单个JSON对象转为模型实例，再放入列表
  final singleProblem = ProblemWithCommentModel.fromJson(response.data as Map<String, dynamic>);
  final problemList = [singleProblem];
  print(problemList);
}

场景2：获取多个Problem对象的列表 #

如果你的目标是获取列表，需确认接口地址是否正确，应该请求不带ID的列表接口：

Future<void> getProblem() async {
  final response = await dio.get('https://localhost:7050/api/Problem', // 移除末尾的/1
      options: Options(
        headers: {"content-type": "application/json"},
      ));
  final problemsJsonList = response.data as List<dynamic>;
  final problemList = problemsJsonList.map((e) => ProblemWithCommentModel.fromJson(e as Map<String, dynamic>)).toList();
  print(problemList);
}

额外代码修正 #

你的Comments类存在语法错误，part of 'Comments.dart';需放在文件开头而非类内部，修正后的示例代码：

part of 'Comments.dart';

// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************

class Comments
{
  final String userName;
  final int id;
  final int userId;
  final int problemId;
  final String about;
  final String date;

  Comments({
    required this.userName,
    required this.id,
    required this.userId,
    required this.problemId,
    required this.about,
    required this.date,
});

  factory Comments.fromJson(Map<String, dynamic> json) => _$CommentsFromJson(json);

  Map<String, dynamic> toJson() => _$CommentsToJson(this);
}

Comments _$CommentsFromJson(Map<String, dynamic> json) => Comments(
      userName: json['userName'] as String,
      id: json['id'] as int,
      userId: json['userId'] as int,
      problemId: json['problemId'] as int,
      about: json['about'] as String,
      date: json['date'] as String,
    );

Map<String, dynamic> _$CommentsToJson(Comments instance) => <String, dynamic>{
      'userName': instance.userName,
      'id': instance.id,
      'userId': instance.userId,
      'problemId': instance.problemId,
      'about': instance.about,
      'date': instance.date,
    };

内容的提问来源于stack exchange，提问作者Aidars Show