Swift 5.1•iOS 13

你可以使用苹果在iOS 13中引入的RelativeDateFormatter。

let exampleDate = Date().addingTimeInterval(-15000)

let formatter = RelativeDateTimeFormatter()
formatter.unitsStyle = .full
let relativeDate = formatter.localizedString(for: exampleDate, relativeTo: Date())

print(relativeDate) // 4 hours ago

参见如何使用RelativeDateTimeFormatter显示相对日期和时间。

结合扩展+ DateComponentsFormatter从@leo-dabus的答案

Xcode 8.3•Swift 3.1

extension DateComponentsFormatter {
    func difference(from fromDate: Date, to toDate: Date) -> String? {
        self.allowedUnits = [.year,.month,.weekOfMonth,.day]
        self.maximumUnitCount = 1
        self.unitsStyle = .full
        return self.string(from: fromDate, to: toDate)
    }
}

let dateComponentsFormatter = DateComponentsFormatter()
dateComponentsFormatter.difference(from: Date(), to: Date(timeIntervalSinceNow: 4000000)) // "1 month"

对于XCode版本8.3.3和Swift 3.0:

    let dateFormatter = DateFormatter()
    dateFormatter.dateStyle = .medium
    dateFormatter.timeStyle = .short

    var beginDate = "2017-08-24 12:00:00"
    var endDate = "2017-09-07 12:00:00"


    let startDateTime = dateFormatter.date(from: beginDate) //according to date format your date string
    print(startDateTime ?? "") //Convert String to Date

    let endDateTime = dateFormatter.date(from: endDate) //according to date format your date string
    print(endDateTime ?? "") //Convert String to Date

    let dateComponentsFormatter = DateComponentsFormatter()
    dateComponentsFormatter.allowedUnits = [NSCalendar.Unit.minute,NSCalendar.Unit.hour,NSCalendar.Unit.day]


   let interval = endDateTime!.timeIntervalSince(startDateTime!)
   var diff = dateComponentsFormatter.string(from: interval)!

   print(diff)

   var day_i  = 0
   var hour_i = 0
   var min_i = 0


     if (diff.contains("d"))
       {
              let day = diff.substring(to: (diff.range(of: "d")?.lowerBound)!)

               day_i  = Int(day)!
               print ("day --> \(day_i)")

               diff = diff.substring(from:(diff.range(of : " ")?.upperBound )!)
               print(diff)
       }


       let hour = diff.substring(to: (diff.range(of : ":")?.lowerBound )!)
       hour_i  = Int(hour)!
       print ("hour --> \(hour_i)")

       let min = diff.substring(from: (diff.range(of : ":")?.upperBound )!)
       min_i  = Int(min)!
       print ("min --> \(min_i)")

以下是我对上述Swift 3的回答。这是截至2016年11月，Xcode发布版本为8.2 Beta (8C23)。使用上述Sagar和Emin的一些建议，有时不得不让Xcode自动完成来建议语法。在这个测试版中，语法似乎真的发生了变化。我从一个DatePicker:

let calendar = NSCalendar.current as NSCalendar
let currentDate = Date()
let date1 = calendar.startOfDay(for: buyDate!)
let date2 = calendar.startOfDay(for: currentDate)      
let flags = NSCalendar.Unit.day
let components = calendar.components(flags, from: date1, to: date2)
NSLog(" day= \(components.day)")

使用Swift 3，根据您的需要，您可以选择以下两种方式之一来解决您的问题。

1. 向用户显示两个日期之间的差异

你可以使用DateComponentsFormatter为你的应用程序界面创建字符串。DateComponentsFormatter有一个maximumUnitCount属性，声明如下:

var maximumUnitCount: Int { get set }

使用此属性可限制结果字符串中显示的单位数量。例如，将此属性设置为2，而不是“1h 10m, 30s”，生成的字符串将是“1h 10m”。当空间受限或希望将值舍入到最近的大单位时，请使用此属性。

通过将maximumUnitCount的值设置为1，可以保证仅以一个DateComponentsFormatter的单位(年、月、日、小时或分钟)显示差异。

下面的Playground代码显示了如何显示两个日期之间的差异:

import Foundation

let oldDate = Date(timeIntervalSinceReferenceDate: -16200)
let newDate = Date(timeIntervalSinceReferenceDate: 0)

let dateComponentsFormatter = DateComponentsFormatter()
dateComponentsFormatter.allowedUnits = [NSCalendar.Unit.year, .month, .day, .hour, .minute]
dateComponentsFormatter.maximumUnitCount = 1
dateComponentsFormatter.unitsStyle = DateComponentsFormatter.UnitsStyle.full
let timeDifference = dateComponentsFormatter.string(from: oldDate, to: newDate)

print(String(reflecting: timeDifference)) // prints Optional("5 hours")

注意，DateComponentsFormatter对结果进行四舍五入。因此，4小时和30分钟的差异将显示为5小时。

如果你需要重复这个操作，你可以重构你的代码:

import Foundation

struct Formatters {

    static let dateComponentsFormatter: DateComponentsFormatter = {
        let dateComponentsFormatter = DateComponentsFormatter()
        dateComponentsFormatter.allowedUnits = [NSCalendar.Unit.year, .month, .day, .hour, .minute]
        dateComponentsFormatter.maximumUnitCount = 1
        dateComponentsFormatter.unitsStyle = DateComponentsFormatter.UnitsStyle.full
        return dateComponentsFormatter
    }()

}

extension Date {
    
    func offset(from: Date) -> String? {
        return Formatters.dateComponentsFormatter.string(from: oldDate, to: self)
    }
    
}

let oldDate = Date(timeIntervalSinceReferenceDate: -16200)
let newDate = Date(timeIntervalSinceReferenceDate: 0)

let timeDifference = newDate.offset(from: oldDate)
print(String(reflecting: timeDifference)) // prints Optional("5 hours")

2. 在不设置格式的情况下获取两个日期之间的差异

如果不需要将两个日期之间的差异格式化显示给用户，则可以使用Calendar。日历有一个方法dateComponents(_:from:to:)，它有以下声明:

func dateComponents(_ components: Set<Calendar.Component>, from start: Date, to end: Date) -> DateComponents

返回两个日期的差值。

下面使用dateComponents(_:from:to:)的Playground代码展示了如何通过只返回一种日历类型的差异来检索两个日期之间的差异。组件(年、月、日、小时或分钟)。

import Foundation

let oldDate = Date(timeIntervalSinceReferenceDate: -16200)
let newDate = Date(timeIntervalSinceReferenceDate: 0)

let descendingOrderedComponents = [Calendar.Component.year, .month, .day, .hour, .minute]
let dateComponents = Calendar.current.dateComponents(Set(descendingOrderedComponents), from: oldDate, to: newDate)
let arrayOfTuples = descendingOrderedComponents.map { ($0, dateComponents.value(for: $0)) }

for (component, value) in arrayOfTuples {
    if let value = value, value > 0 {
        print(component, value) // prints hour 4
        break
    }
}

如果你需要重复这个操作，你可以重构你的代码:

import Foundation

extension Date {
    
    func offset(from: Date) -> (Calendar.Component, Int)? {
        let descendingOrderedComponents = [Calendar.Component.year, .month, .day, .hour, .minute]
        let dateComponents = Calendar.current.dateComponents(Set(descendingOrderedComponents), from: from, to: self)
        let arrayOfTuples = descendingOrderedComponents.map { ($0, dateComponents.value(for: $0)) }
        
        for (component, value) in arrayOfTuples {
            if let value = value, value > 0 {
                return (component, value)
            }
        }
        
        return nil
    }

}

let oldDate = Date(timeIntervalSinceReferenceDate: -16200)
let newDate = Date(timeIntervalSinceReferenceDate: 0)

if let (component, value) = newDate.offset(from: oldDate) {
    print(component, value) // prints hour 4
}

这是一个较短的版本:基本上我现在尝试获得post时间戳与Date()之间的差异。

// MARK: - UPDATE Time Stamp
static func updateTimeStampPost(postTimeStamp: Date?, _ completion: (_ finalString: String?) -> Void) {
    // date in the current state
    let date = Date()
    let dateComponentFormatter = DateComponentsFormatter()

    // change the styling date, wether second minute or hour
    dateComponentFormatter.unitsStyle = .abbreviated
    dateComponentFormatter.allowedUnits = [.second, .minute, .hour, .day, .weekOfMonth]
    dateComponentFormatter.maximumUnitCount = 1

    // return the date new format as a string in the completion
    completion(dateComponentFormatter.string(from: postTimeStamp!, to: date))
}