list - 由列表分配的值，每次迭代更改

Question

这是按事件将事件分组的功能。它以List<EventK>开头，其中包含要排序的所有元素。结果是Map<DateTime, List<EventK>>。

问题出在currentDayEvents上。一旦将其分配给_events，并且currentDayEvents的值在不同的迭代中更改，那么_events的值也会更改。如何在函数外获取_events的永久值？

void _getEvents()async{

    setState(() {
      isLoading = true;
    });

    List<EventK> events = await EventApi.getPersonalEvents();
    List<EventK> currentDayEvents = [];

    DateTime currentDay;

    for(int i = 0; i<events.length-1; i++){

      currentDay = events[i].startTime;
      currentDayEvents.add(events[i]);

      for(int j=i+1; j<events.length; j++){

        DateTime analyzedDay = events[j].startTime;

        if(currentDay.year == analyzedDay.year &&
            currentDay.month == analyzedDay.month &&
            currentDay.day == analyzedDay.day
        ){
          currentDayEvents.add(events[j]);
          events.removeAt(j);
          j -= 1;
        }

      }

      _events.putIfAbsent(currentDay, ()=>currentDayEvents);
      currentDayEvents.clear();

    }

    setState(() {
      isLoading = false;
    });
  }

Answer 1

将currentDayEvents的声明移至for循环内，以在每次迭代时重新初始化一个新对象。这样，您可以删除currentDayEvents.clear()。

for(int i = 0; i<events.length-1; i++){

  currentDay = events[i].startTime;
  var currentDayEvents = [events[i]];

  for(int j=i+1; j<events.length; j++){

    DateTime analyzedDay = events[j].startTime;

    if(currentDay.year == analyzedDay.year &&
        currentDay.month == analyzedDay.month &&
        currentDay.day == analyzedDay.day
    ){
      currentDayEvents.add(events[j]);
      events.removeAt(j);
      j -= 1;
    }

  }

  _events.putIfAbsent(currentDay, ()=>currentDayEvents);
}