Dart，无法调用Generic的方法 [英] Dart, Can't call Generic's method

问题描述

我正在尝试创建一个抽象数据模型，在该模型中我传递数据并键入a，然后返回列表，但是当我无法调用 T.fromJson（）时方法，请注意，传递类型具有方法 fromJson（）

I am trying to create an abstract data model where i pass data and type a and then is return list, but when i can't call T.fromJson() method, note that passes type has method fromJson()

class DataList<T> {
  final bool success; 
  dynamic data;


  InfosResponse({
    this.success,
    List<dynamic> data,   
  }) {
    castDataToList(data);
  }

  factory DataList.fromJson(Map<String, dynamic> json) {
    return DataList(
      success: json['success'],
      data: json['data'],
    );
  }

  void castDataToList(jsonData) {
    this.data = List<T>.from(jsonData.map((x) => T.fromJson(x)));
  }
}

推荐答案

您无法在类型变量上调用静态方法。静态方法必须在编译时已知，并且类型变量的值要在运行时才知道。

You cannot call static methods on type variables. Static methods must be known at compile-time, and the value of a type variable is not known until run-time.

您可以使用您所使用的方法对类进行参数化要调用：

You can parameterize your class with the method that you want to call:

class DataList<T> {
  final bool success; 
  dynamic data;
  T dynamic Function(Object) fromJson;

  DataList({
    this.success,
    List<dynamic> data,   
    this.fromJson;
  }) {
    castDataToList(data);
  }

  factory DataList.fromJson(Map<String, dynamic> json, T fromJson(Object o)) {
     return DataList(
        success: json['success'],
        data: json['data'],
        fromJson: fromJson,
    );
  }

  void castDataToList(jsonData) {
    this.data = List<T>.from(jsonData.map((x) => fromJson(x)));
  }
}

当您要使用具有某种类型的类时， Foo 具有 fromJson 静态方法，您将实例创建为：

When you want to use the class with a type, Foo which has a fromJson static method, you create the instance as:

var dataList = DataList<Foo>fromJson(someJsonMap, Foo.fromJson);

这会将 Foo.fromjson 函数传递给该类，然后可以在需要时使用它。

This passes the Foo.fromjson function to the class, which can then use it when needed.

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