查看 NSCalendar 的 startOfDayForDate 方法来查找当天的开始.

Check out NSCalendar's startOfDayForDate method to find the start of the current day.

要查找当天的结束时间，您需要在从 startOfDayForDate 返回的日期中添加一天，然后减去一秒.

To find the end of the current day, you'll want to add a day to the date returned from startOfDayForDate and then subtract one second.