objective-c - 如何在今天午夜获取 NSDate 对象？

Question

获取代表当天午夜的 NSDate 对象的最有效方法是什么？

Answer 1

iOS 8 中的新 API

iOS 8 在 NSCalendar 上包含一个名为 startOfDayForDate 的新方法，它非常易于使用:

let startOfToday = NSCalendar.currentCalendar().startOfDayForDate(NSDate())

苹果的描述:

This API returns the first moment date of a given date. Pass in [NSDate date], for example, if you want the start of "today". If there were two midnights, it returns the first. If there was none, it returns the first moment that did exist.

关于时区的更新:

由于 startOfDayForDate 是 NSCalendar 上的一个方法，它使用 NSCalendar 的时区。因此，如果我想知道现在是在纽约几点钟，今天从洛杉矶开始，我可以这样做:

let losAngelesCalendar = NSCalendar.currentCalendar().copy() as! NSCalendar
losAngelesCalendar.timeZone = NSTimeZone(name: "America/Los_Angeles")!

let dateTodayBeganInLosAngeles = losAngelesCalendar.startOfDayForDate(NSDate())
dateTodayBeganInLosAngeles.timeIntervalSince1970

let dateFormatter = NSDateFormatter()
dateFormatter.dateStyle = .MediumStyle
dateFormatter.timeStyle = .ShortStyle
dateFormatter.timeZone = NSTimeZone(name: "America/New_York")!
let timeInNewYorkWhenTodayBeganInLosAngeles = dateFormatter.stringFromDate(dateTodayBeganInLosAngeles)
print(timeInNewYorkWhenTodayBeganInLosAngeles) // prints "Jul 29, 2015, 3:00 AM"