您如何为列表中的单个项目（而不是整个列表）编写设置器？

Question

我的模型中有一个包含 bool 列表的类。在我的 UI 中，我想通过 setter 在列表中的单个项目中设置布尔状态（这样我也可以保存它）。我无法弄清楚语法（或者这是否是一个有效的做法）。

   ///This is OK
   set notificationDismissed(bool notificationDismissed){
     _notificationDismissed = notificationDismissed;
     saveParameterBoolean(_notificationDismissedKey, 
  _notificationDismissed);
    }
  bool get notificationDismissed => _notificationDismissed;


  ///This is OK too
  List<bool> get questionsAnswered => _questionsAnswered;
  set questionsAnswered(List<bool> questionsAnswered){
    _questionsAnswered = questionsAnswered;
    for(int i=0; i<_questionAnsweredParamKeys.length; i++ ){
      saveParameterBoolean(_questionAnsweredParamKeys[i], 
  _questionsAnswered[i]);
    }
    updateState();
  }

  ///This is not OK !!!! but should show what I want to do
  List<bool> get questionsAnswered[index] => _questionsAnswered[index];
  set questionsAnswered[index](bool questionsAnswered[index]){
    _questionsAnswered[index] = questionsAnswered[index];
    saveParameterBoolean(_questionAnsweredParamKeys[index], 
  _questionsAnswered[index]);
    updateState();
  }

我知道我在这里遗漏了一些明显的东西，非常感谢任何帮助

Answer 1

get 和 set 函数不能接受任何参数。最简单的方法是使用普通函数：

bool getQuestionsAnswered(int index) =>  _questionsAnswered[index];

void setQuestionsAnswered(int index, bool value) {
  _questionsAnswered[index] = value;
  saveParameterBoolean(_questionAnsweredParamKeys[index], _questionsAnswered[index]);
  updateState();
}

另一种选择是将_questionsAnswered 从List 更改为实现operator []（获取元素）和operator []=（设置元素）的自定义类，然后您可以让它们执行随心所欲。