class People {
  String name; // 姓名
  String area; // 地区
  String sex; // 性别
  int age; // 年龄

  People({this.name, this.area, this.sex, this.age});

  /// Map 转实体类
  People.fromJson(Map<String, dynamic> json) {
    this.name = json['name'];
    this.area = json['area'];
    this.sex = json['sex'];
    this.age = json['age'];
  }

  /// 实体类转 Map
  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['name'] = this.name;
    data['area'] = this.area;
    data['sex'] = this.sex;
    data['age'] = this.age;
    return data;
  }
}

声明一个 People 类的对象

People p = People(name: "AllenSu", area: "郑州", sex: "男", age: 18);

Map<String, dynamic> m = p.toJson(); // m:{name: AllenSu, area: 郑州, sex: 男, age: 18}

People p2 = People.fromJson(m); // p2:{name: AllenSu, area: 郑州, sex: 男, age: 18}