xcode 一个日历年中 2 个 NSDates 之间的天数 swift

Days between 2 NSDates in a calendar year swift

提问by Aaron

I'm building a birthday reminder app. I want the user to be able to see how many days it is until somebody's next birthday.

我正在构建一个生日提醒应用程序。我希望用户能够看到距离某人下一个生日还有多少天。

Let's say I have an NSDate()= 2015-06-30 07:21:47 +0000

假设我有一个NSDate()=2015-06-30 07:21:47 +0000

And the NSDatefor the birthday = 1985-08-29 12:00:00 +0000

而NSDate对于生日=1985-08-29 12:00:00 +0000

How would I get the number of days until the next birthday? I've used something like thiswhich gives a negative number of days since the date's actual beginning (which are in the thousands with birthdates). Then with that I would add 365 to the numerical difference until it was positive but it still returns a wonky number. I'm assuming due to leap years or something.

我如何获得下一个生日的天数？我用像这样赋予因为日期的实际开始（这是在数以千计的出生日期）的天负数。然后我会将 365 添加到数字差异中，直到它为正数，但它仍然返回一个不稳定的数字。我假设是由于闰年或其他原因。

Is there a method to this I can implement? Somehow equalize the year components so that it's always comparing from the next birthday and not the original birthdate?

有没有我可以实现的方法？以某种方式均衡年份组件，以便它始终从下一个生日而不是原始生日开始比较？

Edit:

编辑：

Here is the function I am using:

这是我正在使用的功能：

func daysBetween(date1: NSDate, date2: NSDate) -> Int {

    var calendar: NSCalendar = NSCalendar.currentCalendar()

    let date1 = calendar.startOfDayForDate(date1)
    let date2 = calendar.startOfDayForDate(date2)

    let flags = NSCalendarUnit.CalendarUnitDay
    let components = calendar.components(flags, fromDate: date1, toDate: date2, options: nil)

    return components.day
}

With the example dates I posted I would use it like this:

对于我发布的示例日期，我会像这样使用它：

// sampleDate = 1985-08-29 12:00:00 +0000
daysBetween(sampleDate, date2: NSDate())
// --> 10897

Whether positive or negative, the number is in the thousands. I'm looking to equalize that into number of days to the next calendar birthday.

无论是正数还是负数，这个数字都以千计。我希望将其平衡为到下一个日历生日的天数。

回答by Martin R

What you need is to compute the next occurrenceof the (day and month component of the) birthday after today:

您需要的是计算今天之后生日（的日和月部分）的下一次出现：

let cal = NSCalendar.currentCalendar()
let today = cal.startOfDayForDate(NSDate())
let dayAndMonth = cal.components(.CalendarUnitDay | .CalendarUnitMonth,
    fromDate: birthday)
let nextBirthDay = cal.nextDateAfterDate(today,
    matchingComponents: dayAndMonth,
    options: .MatchNextTimePreservingSmallerUnits)!

Remarks:

评论：

• The purpose of the MatchNextTimePreservingSmallerUnitsoption is that if the birthday is on February 29 (in the Gregorian calendar), its next occurrence will be computed as March 1 if the year is not a leap year.

• You might need to check first if the birthday is today, as it seems that nextDateAfterDate()would return the nextbirthday in that case.

• 该MatchNextTimePreservingSmallerUnits选项的目的是，如果生日是 2 月 29 日（在公历中），那么如果该年不是闰年，那么它的下一次出现将被计算为 3 月 1 日。

• 您可能需要先检查生日是否为today，因为在这种情况下似乎nextDateAfterDate()会返回下一个生日。

Then you can compute the difference in days as usual:

然后您可以像往常一样计算天数差异：

let diff = cal.components(.CalendarUnitDay,
    fromDate: today,
    toDate: nextBirthDay,
    options: nil)
println(diff.day)

---

---

Update for Swift 2.2 (Xcode 7.3):

Swift 2.2 (Xcode 7.3) 的更新：

let cal = NSCalendar.currentCalendar()
let today = cal.startOfDayForDate(NSDate())
let dayAndMonth = cal.components([.Day, .Month],
                                 fromDate: birthday)
let nextBirthDay = cal.nextDateAfterDate(today,
                                         matchingComponents: dayAndMonth,
                                         options: .MatchNextTimePreservingSmallerUnits)!

let diff = cal.components(.Day,
                          fromDate: today,
                          toDate: nextBirthDay,
                          options: [])
print(diff.day)

---

---

Update for Swift 3 (Xcode 8 GM):

Swift 3 (Xcode 8 GM) 的更新：

let cal = Calendar.current
let today = cal.startOfDay(for: Date())
let dayAndMonth = cal.dateComponents([.day, .month], from: birthday)
let nextBirthDay = cal.nextDate(after: today, matching: dayAndMonth,
                                matchingPolicy: .nextTimePreservingSmallerComponents)!

let diff = cal.dateComponents([.day], from: today, to: nextBirthDay)
print(diff.day!)

回答by Ricardo Barroso

Btw, in case anyone needs here is the @Aaron function in Swift 3:

顺便说一句，如果有人需要这里是 Swift 3 中的 @Aaron 函数：

func daysBetween(date1: Date, date2: Date) -> Int {
    let calendar = Calendar.current

    let date1 = calendar.startOfDay(for: date1)
    let date2 = calendar.startOfDay(for: date2)

    let components = calendar.dateComponents([Calendar.Component.day], from: date1, to: date2)

    return components.day ?? 0
}