在 Flutter 类中初始化多个 DateTime 变量

Question

我有一个 Reminder 类，它有两个日期变量 - startDate 和 endDate。

class Reminder {
  
  final String name;
  final String type;
  final DateTime startDate;
  final String repeatFrequency;
  final DateTime endDate;
  
  Reminder({this.name = "", this.type = "", DateTime startDate = DateTime.utc(2021,1,1),
            this.repeatFrequency = "", DateTime endDate = DateTime.utc(2021,1,1)})
  
}

当我初始化类时，我收到一条错误消息“可选参数的默认值必须是常量”。基于this article，我尝试了以下方法：

  Reminder({this.name = "", this.type = "", DateTime? startDate,
            this.repeatFrequency = "", DateTime? endDate}) : 
  this.startDate = (startDate != null ? startDate : DateTime.utc(2021,1,1))

这种方法现在似乎有效，但是我只能对 startDate 而不是 endDate 这样做。有没有办法用这种方法初始化两个变量？

Answer 1

你可以试试下面这段代码：

  Reminder({this.name = "", this.type = "", DateTime? startDate,
    this.repeatFrequency = "", DateTime? endDate}) :
        this.startDate = (startDate != null ? startDate : DateTime.utc(2021,1,1)), 
        this.endDate = endDate ?? DateTime.utc(2021,1,1);