计算 Swift 中两个日期之间的差异

Question

我见过很多方法如何根据特定日期组件计算两个日期之间的差异，例如以天、小时、月等为单位（参见 this answer on Whosebug）：

Calendar.current.dateComponents([.hour], from: fromDate, to: toDate).hour
Calendar.current.dateComponents([.day], from: fromDate, to: toDate).day
Calendar.current.dateComponents([.month], from: fromDate, to: toDate).month

我没有看到的是如何用实际的 Date 对象进行计算。像

func computeNewDate(from fromDate: Date, to toDate: Date) -> Date    
     let delta = toDate - fromDate
     let today = Date()
     if delta < 0 {
         return today
     } else {
         return today + delta
     }
}

我已经看到 iOS 10 中引入的 DateInterval 类型，但根据文档

[it] does not support reverse intervals i.e. intervals where the duration is less than 0 and the end date occurs earlier in time than the start date.

这使得使用日期进行计算本来就很困难 – 特别是当您不知道哪个日期较早时。

是否有任何简洁明了的方法直接计算 Dates 之间的时间差（并再次将它们添加到 Date 个实例）不用计算 timeIntervalSinceReferenceDate?

Answer 1

怎么样……

func computeNewDate(from fromDate: Date, to toDate: Date) -> Date {
    let delta = Calendar.current.dateComponents([.second], from: fromDate, to: toDate).second!
    return Calendar.current.date(byAdding: .second, value: delta, to: Date())!
}

Answer 2

我最终为 Date 创建了一个自定义运算符：

extension Date {

    static func - (lhs: Date, rhs: Date) -> TimeInterval {
        return lhs.timeIntervalSinceReferenceDate - rhs.timeIntervalSinceReferenceDate
    }

}

有了这个运算符，我现在可以在更抽象的层面上计算两个日期之间的差异，而不用关心 timeIntervalSinceReferenceDate 或参考日期到底是什么——而且不会丢失精度，例如：

let delta = toDate - fromDate

显然，我没有做太多改变，但对我来说它更具可读性和结果：Swift 已经为 Date 和 TimeInterval:

/// Returns a `Date` with a specified amount of time added to it.
public static func + (lhs: Date, rhs: TimeInterval) -> Date

所以它已经支持

Date + TimeInterval = Date

所以应该也支持

Date - Date = TimeInterval

在我看来，这就是我在 - 运算符的简单实现中添加的内容。现在我可以完全按照我的问题中提到的那样简单地编写示例函数：

func computeNewDate(from fromDate: Date, to toDate: Date) -> Date    
     let delta = toDate - fromDate // `Date` - `Date` = `TimeInterval`
     let today = Date()
     if delta < 0 {
         return today
     } else {
         return today + delta // `Date` + `TimeInterval` = `Date`
     }
}

很可能这有一些我目前还没有意识到的缺点，我很想听听你对此的看法。

Answer 3

简直toDate.timeIntervalSince(fromDate).

要在不添加任何扩展的情况下重新实现您的函数：

func computeNewDate(from fromDate: Date, to toDate: Date) -> Date  {  
     let delta = toDate.timeIntervalSince(fromDate) 
     let today = Date()
     if delta < 0 {
         return today
     } else {
         return today.addingTimeInterval(delta) 
     }
}

Answer 4

您可以使用自定义运算符进行扩展，return 元组

extension Date {

    static func -(recent: Date, previous: Date) -> (month: Int?, day: Int?, hour: Int?, minute: Int?, second: Int?) {
        let day = Calendar.current.dateComponents([.day], from: previous, to: recent).day
        let month = Calendar.current.dateComponents([.month], from: previous, to: recent).month
        let hour = Calendar.current.dateComponents([.hour], from: previous, to: recent).hour
        let minute = Calendar.current.dateComponents([.minute], from: previous, to: recent).minute
        let second = Calendar.current.dateComponents([.second], from: previous, to: recent).second

        return (month: month, day: day, hour: hour, minute: minute, second: second)
    }

}

使用：

let interval = Date() - updatedDate
print(interval.day)
print(interval.month)
print(interval.hour)

Answer 5

我找到了一个内置解决方案来计算两个日期之间的差异。

let delta = toDate.timeIntervalSince(fromDate)

Answer 6

您可以使用：

let delta = fromDate.distance(to: toDate)

计算 Swift 中两个日期之间的差异

Calculating the difference between two dates in Swift

date

ios

dateinterval

swift