我有一個 Reminder 類，它有兩個日期變數 - 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)})
}
當我初始化該類時，我收到一條錯誤訊息，提示“可選引數的默認值必須是常量”。基于這篇文章，我嘗試了以下方法：
Reminder({this.name = "", this.type = "", DateTime? startDate,
this.repeatFrequency = "", DateTime? endDate}) :
this.startDate = (startDate != null ? startDate : DateTime.utc(2021,1,1))
這種方法現在似乎有效，但是我只能為 startDate 而不是 endDate 這樣做。有沒有辦法用這種方法初始化兩個變數？
uj5u.com熱心網友回復：
您可以嘗試使用以下代碼：
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);
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