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)")

Xcode 8.3•Swift 3.1或更高版本

您可以使用日历来帮助您创建一个扩展来进行日期计算，如下所示:

extension Date {
    /// Returns the amount of years from another date
    func years(from date: Date) -> Int {
        return Calendar.current.dateComponents([.year], from: date, to: self).year ?? 0
    }
    /// Returns the amount of months from another date
    func months(from date: Date) -> Int {
        return Calendar.current.dateComponents([.month], from: date, to: self).month ?? 0
    }
    /// Returns the amount of weeks from another date
    func weeks(from date: Date) -> Int {
        return Calendar.current.dateComponents([.weekOfMonth], from: date, to: self).weekOfMonth ?? 0
    }
    /// Returns the amount of days from another date
    func days(from date: Date) -> Int {
        return Calendar.current.dateComponents([.day], from: date, to: self).day ?? 0
    }
    /// Returns the amount of hours from another date
    func hours(from date: Date) -> Int {
        return Calendar.current.dateComponents([.hour], from: date, to: self).hour ?? 0
    }
    /// Returns the amount of minutes from another date
    func minutes(from date: Date) -> Int {
        return Calendar.current.dateComponents([.minute], from: date, to: self).minute ?? 0
    }
    /// Returns the amount of seconds from another date
    func seconds(from date: Date) -> Int {
        return Calendar.current.dateComponents([.second], from: date, to: self).second ?? 0
    }
    /// Returns the a custom time interval description from another date
    func offset(from date: Date) -> String {
        if years(from: date)   > 0 { return "\(years(from: date))y"   }
        if months(from: date)  > 0 { return "\(months(from: date))M"  }
        if weeks(from: date)   > 0 { return "\(weeks(from: date))w"   }
        if days(from: date)    > 0 { return "\(days(from: date))d"    }
        if hours(from: date)   > 0 { return "\(hours(from: date))h"   }
        if minutes(from: date) > 0 { return "\(minutes(from: date))m" }
        if seconds(from: date) > 0 { return "\(seconds(from: date))s" }
        return ""
    }
}

使用日期组件格式化程序

let dateComponentsFormatter = DateComponentsFormatter()
dateComponentsFormatter.allowedUnits = [.second, .minute, .hour, .day, .weekOfMonth, .month, .year]
dateComponentsFormatter.maximumUnitCount = 1
dateComponentsFormatter.unitsStyle = .full
dateComponentsFormatter.string(from: Date(), to: Date(timeIntervalSinceNow: 4000000))  // "1 month"

let date1 = DateComponents(calendar: .current, year: 2014, month: 11, day: 28, hour: 5, minute: 9).date!
let date2 = DateComponents(calendar: .current, year: 2015, month: 8, day: 28, hour: 5, minute: 9).date!

let years = date2.years(from: date1)     // 0
let months = date2.months(from: date1)   // 9
let weeks = date2.weeks(from: date1)     // 39
let days = date2.days(from: date1)       // 273
let hours = date2.hours(from: date1)     // 6,553
let minutes = date2.minutes(from: date1) // 393,180
let seconds = date2.seconds(from: date1) // 23,590,800

let timeOffset = date2.offset(from: date1) // "9M"

let date3 = DateComponents(calendar: .current, year: 2014, month: 11, day: 28, hour: 5, minute: 9).date!
let date4 = DateComponents(calendar: .current, year: 2015, month: 11, day: 28, hour: 5, minute: 9).date!

let timeOffset2 = date4.offset(from: date3) // "1y"

let date5 = DateComponents(calendar: .current, year: 2017, month: 4, day: 28).date!
let now = Date()
let timeOffset3 = now.offset(from: date5) // "1w"

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)")

如果你的目的是获得两个日期之间的确切天数，你可以这样解决这个问题:

// Assuming that firstDate and secondDate are defined
// ...

var calendar: NSCalendar = NSCalendar.currentCalendar()

// Replace the hour (time) of both dates with 00:00
let date1 = calendar.startOfDayForDate(firstDate)
let date2 = calendar.startOfDayForDate(secondDate)

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

components.day  // This will return the number of day(s) between dates

对Swift 3.0略有修改的代码

let calendar = NSCalendar.current as NSCalendar

// Replace the hour (time) of both dates with 00:00
let date1 = calendar.startOfDay(for: startDateTime)
let date2 = calendar.startOfDay(for: endDateTime)

let flags = NSCalendar.Unit.day
let components = calendar.components(flags, from: date1, to: date2, options: [])

return components.day!

  func dateDiff(dateStr:String) -> String {
        var f:NSDateFormatter = NSDateFormatter()
        f.timeZone = NSTimeZone.localTimeZone()
        f.dateFormat = "yyyy-M-dd'T'HH:mm:ss.SSSZZZ"
        
        var now = f.stringFromDate(NSDate())
        var startDate = f.dateFromString(dateStr)
        var endDate = f.dateFromString(now)
        var calendar: NSCalendar = NSCalendar.currentCalendar()
        
        let calendarUnits = NSCalendarUnit.CalendarUnitWeekOfMonth | NSCalendarUnit.CalendarUnitDay | NSCalendarUnit.CalendarUnitHour | NSCalendarUnit.CalendarUnitMinute | NSCalendarUnit.CalendarUnitSecond
        let dateComponents = calendar.components(calendarUnits, fromDate: startDate!, toDate: endDate!, options: nil)
        
        let weeks = abs(dateComponents.weekOfMonth)
        let days = abs(dateComponents.day)
        let hours = abs(dateComponents.hour)
        let min = abs(dateComponents.minute)
        let sec = abs(dateComponents.second)
        
        var timeAgo = ""

        if (sec > 0){
            if (sec > 1) {
                timeAgo = "\(sec) Seconds Ago"
            } else {
                timeAgo = "\(sec) Second Ago"
            }
        }
        
        if (min > 0){
            if (min > 1) {
                timeAgo = "\(min) Minutes Ago"
            } else {
                timeAgo = "\(min) Minute Ago"
            }
        }
        
        if(hours > 0){
            if (hours > 1) {
                timeAgo = "\(hours) Hours Ago"
            } else {
                timeAgo = "\(hours) Hour Ago"
            }
        }
        
        if (days > 0) {
            if (days > 1) {
                timeAgo = "\(days) Days Ago"
            } else {
                timeAgo = "\(days) Day Ago"
            }
        }
        
        if(weeks > 0){
            if (weeks > 1) {
                timeAgo = "\(weeks) Weeks Ago"
            } else {
                timeAgo = "\(weeks) Week Ago"
            }
        }
        
        print("timeAgo is===> \(timeAgo)")
        return timeAgo;
    }