Flutter中JSON解析报错：_Map<String, dynamic>无法转为LoginResponse

核心问题1：直接赋值类型不匹配 #

jsonDecode仅能将JSON字符串转换为Map<String, dynamic>类型，不能直接赋值给LoginResponse对象，必须通过模型类的fromJson工厂方法完成转换：

// 错误写法
LoginResponse response = jsonDecode(loginResponse.body);

// 正确写法
Map<String, dynamic> jsonMap = jsonDecode(loginResponse.body);
LoginResponse response = LoginResponse.fromJson(jsonMap);

核心问题2：字段类型不匹配 #

JSON中userId是数字类型（29922），但你的UserData类将其定义为String，强转as String会触发类型转换异常，两种修复方式任选：

方式一：将userId改为int类型 #

class UserData{
  final int userId;

  UserData({required this.userId});

  factory UserData.fromJson(Map<String, dynamic> json) {
    return UserData(
      userId: json['userId'] as int
    );
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['userId'] = this.userId;
    return data;
  }
}

方式二：保留String类型，将数字转为字符串 #

factory UserData.fromJson(Map<String, dynamic> json) {
  return UserData(
    userId: json['userId'].toString()
  );
}

可选优化：补充缺失字段 #

JSON中userData包含applicationId和siteId字段，但你的模型类未定义，若业务需要使用这两个字段，建议补充：

class UserData{
  final int userId;
  final int applicationId;
  final int siteId;

  UserData({required this.userId, required this.applicationId, required this.siteId});

  factory UserData.fromJson(Map<String, dynamic> json) {
    return UserData(
      userId: json['userId'] as int,
      applicationId: json['applicationId'] as int,
      siteId: json['siteId'] as int,
    );
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['userId'] = this.userId;
    data['applicationId'] = this.applicationId;
    data['siteId'] = this.siteId;
    return data;
  }
}

最终可运行的main.dart代码 #

//loginResponse.body是JSON数据
http.Response loginResponse = await postRequest();
Map<String, dynamic> jsonMap = jsonDecode(loginResponse.body);
LoginResponse response = LoginResponse.fromJson(jsonMap);
print('status:>>${response.verificationStatus}');
print('userId:>>${response.userData.userId}');

内容的提问来源于stack exchange，提问作者Sreejith Sree