无法从工厂构造函数访问实例成员。颤振误差

Question

我收到一个错误，例如：

无法从工厂构造函数访问实例成员。尝试删除对实例成员的引用。

有什么解决办法吗？

class DepartureModel {
  String route;
  String departureTime;
  String arrivalTime;
  String tourType;
  List<String> daysOfWeek;

  DepartureModel({
    required this.route,
    required this.departureTime,
    required this.arrivalTime,
    required this.tourType,
    required this.daysOfWeek,
  });

  //method that assign values to respective datatype vairables

  factory DepartureModel.fromJson(Map<String, dynamic> json) {
    return DepartureModel(
      route: json['route'],
      departureTime: json['departureTime'],
      arrivalTime: json['arrivalTime'],
      tourType: json['tourType'],
      daysOfWeek: json["daysOfWeek"].forEach(
        (day) {
          daysOfWeek.add(day);
        },
      ),
    );
  }

Answer 1

您试图daysOfWeek在分配它时访问它，这就是编译器抱怨的原因，因为它还不知道 的值daysOfWeek。

一个真正有效的解决方法是在工厂构造函数中创建一个新列表，并在完成循环后将其分配给daysOfWeek这样的：

factory DepartureModel.fromJson(Map<String, dynamic> json) {
    final tempDaysOfWeek = [];
    json["daysOfWeek"].forEach((day) => tempDaysOfWeek.add(day));
    return DepartureModel(
      route: json['route'],
      departureTime: json['departureTime'],
      arrivalTime: json['arrivalTime'],
      tourType: json['tourType'],
      daysOfWeek: tempDaysOfWeek,
    );

您还可以命名tempDaysOfWeek为daysOfWeek作用域将负责调用哪个变量，但这可以减轻混乱。

不带 的更简洁用法如下forEach：

factory DepartureModel.fromJson(Map<String, dynamic> json) {
    return DepartureModel(
      route: json['route'],
      departureTime: json['departureTime'],
      arrivalTime: json['arrivalTime'],
      tourType: json['tourType'],
      daysOfWeek: (json["daysOfWeek"] as List).cast<String>(),
    );