如何只更改DateTime中的时间？

Question

我有一个DateTime，我正在尝试用它做两件事。1：只更新日期和月份。2：只更新时间。我如何实现这一点？

  DateTime currentDateTime = DateTime.now();

  void updateTime(DateTime newTime) {
       currentDateTime = ?
  }
  void updateDate(DateTime newTime) {
       currentDateTime = ?
  }

有什么方法可以破坏< code>currentDateTime像< code>DateTime(...当前日期时间，..newTime)

Answer 1

要仅更新时间，您可以使用星期几。这是我能做到的方法

DateTime currentDateTime = DateTime.now();

void updateTime(TimeOfDay newTime) {
  // 2020-09-07 09:03:24.469
  TimeOfDay time = TimeOfDay(hour: newTime.hour, minute: newTime.minute);
  currentDateTime = DateTime(currentDateTime.year, currentDateTime.month, currentDateTime.month, time.hour, time.minute);
  // 2020-09-09 15:00:00.000
}

void updateDate(DateTime newTime) {
  // 2020-09-09 15:00:00.000
  currentDateTime = DateTime(newTime.year, newTime.month, newTime.day);
  // 2021-01-01 00:00:00.000
}

我希望这是有帮助的。

Answer 2

从日期时间（）属性构造日期时间对象，而不是整个日期时间（）对象。这应该有效。

  DateTime currentDateTime = DateTime.now();

  void updateTime(DateTime currentDateTime, DateTime newTime) {
       currentDateTime = DateTime(
         year: currentDateTime.year,
         month: currentDateTime.month
         day: currentDateTime.day,
         hour: newTime.hour,
         minute: newTime.minute,
         second: newTime.second,
       );
  }

  void updateDate(DateTime currentDateTime, DateTime newDate) {
       currentDateTime = DateTime(
         year: currentDateTime.year,
         month: newTime.month
         day: newTime.day,
         hour: currentDateTime.hour,
         minute: currentDateTime.minute,
         second: currentDateTime.second,
       );
  }

请记住Datetime的构造函数如下所示

DateTime(int year, [int month = 1, int day = 1, int hour = 0, int minute = 0, int second = 0, int millisecond = 0, int microsecond = 0])