Estoy tratando de obtener la diferencia entre la fecha actual como NSDate()y una fecha de un PHP time();llamada, por ejemplo: NSDate(timeIntervalSinceReferenceDate: 1417147270). ¿Cómo hago para obtener la diferencia de tiempo entre las dos fechas? Me gustaría tener una función que compare las dos fechas y if(seconds > 60)luego devuelva minutos, if(minutes > 60)horas de if(hours > 24)devolución y días de devolución, etc.

¿Cómo debo hacer esto?

EDITAR: La respuesta aceptada actual ha hecho exactamente lo que quería hacer. Lo recomiendo para un uso fácil para obtener el tiempo entre dos fechas en la forma que time()usa la función PHP . Si no está familiarizado con PHP, es el tiempo en segundos desde el 1 de enero de 1970. Esto es beneficioso para un back-end en PHP. Si tal vez está utilizando un backend como NodeJS, es posible que desee considerar algunas de las otras opciones que encontrará a continuación.

Xcode 8.3 • Swift 3.1 o posterior

Puede usar el Calendario para ayudarlo a crear una extensión para hacer sus cálculos de fecha de la siguiente manera:

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 ""
    }
}

Uso del formateador de componentes de fecha

let dateComponentsFormatter = DateComponentsFormatter()
dateComponentsFormatter.allowedUnits = [.year,.month,.weekOfMonth,.day,.hour,.minute,.second]
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"

Si alguien necesita mostrar todas las unidades de tiempo, por ejemplo, "horas minutos segundos", no solo "horas". Digamos que la diferencia horaria entre dos fechas es 1 hora 59 minutos 20 segundos. Esta función mostrará "1h 59m 20s".

Aquí está mi código Objective-C:

extension NSDate {

    func offsetFrom(date: NSDate) -> String {

        let dayHourMinuteSecond: NSCalendarUnit = [.Day, .Hour, .Minute, .Second]
        let difference = NSCalendar.currentCalendar().components(dayHourMinuteSecond, fromDate: date, toDate: self, options: [])

        let seconds = "\(difference.second)s"
        let minutes = "\(difference.minute)m" + " " + seconds
        let hours = "\(difference.hour)h" + " " + minutes
        let days = "\(difference.day)d" + " " + hours

        if difference.day    > 0 { return days }
        if difference.hour   > 0 { return hours }
        if difference.minute > 0 { return minutes }
        if difference.second > 0 { return seconds }
        return ""
    }

}

En Swift 3+:

extension Date {

    func offsetFrom(date: Date) -> String {

        let dayHourMinuteSecond: Set<Calendar.Component> = [.day, .hour, .minute, .second]
        let difference = NSCalendar.current.dateComponents(dayHourMinuteSecond, from: date, to: self)

        let seconds = "\(difference.second ?? 0)s"
        let minutes = "\(difference.minute ?? 0)m" + " " + seconds
        let hours = "\(difference.hour ?? 0)h" + " " + minutes
        let days = "\(difference.day ?? 0)d" + " " + hours

        if let day = difference.day, day          > 0 { return days }
        if let hour = difference.hour, hour       > 0 { return hours }
        if let minute = difference.minute, minute > 0 { return minutes }
        if let second = difference.second, second > 0 { return seconds }
        return ""
    }

}

Usted pregunta:

Me gustaría tener una función que compare las dos fechas y si (segundos> 60) devuelve minutos, si (minutos> 60) devuelve horas y si (horas> 24) devuelve días, etc.

Supongo que está tratando de construir una representación de cadena del tiempo transcurrido entre dos fechas. En lugar de escribir su propio código para hacerlo, Apple ya tiene una clase diseñada para hacer precisamente eso. Es decir, use DateComponentsFormatter, establezca los allowedUnitsvalores que tengan sentido para su aplicación, establezca unitsStylelo que desee (por ejemplo .full) y luego llame string(from:to:).

Por ejemplo, en Swift 3:

let previousDate = ...
let now = Date()

let formatter = DateComponentsFormatter()
formatter.unitsStyle = .full
formatter.allowedUnits = [.month, .day, .hour, .minute, .second]
formatter.maximumUnitCount = 2   // often, you don't care about seconds if the elapsed time is in months, so you'll set max unit to whatever is appropriate in your case

let string = formatter.string(from: previousDate, to: now)

Esto también localizará la cadena apropiada para el dispositivo en cuestión.

O, en Swift 2.3:

let previousDate = ...
let now = NSDate()

let formatter = NSDateComponentsFormatter()
formatter.unitsStyle = .Full
formatter.allowedUnits = [.Month, .Day, .Hour, .Minute, .Second]
formatter.maximumUnitCount = 2

let string = formatter.stringFromDate(previousDate, toDate: now)

Si está buscando los valores numéricos reales, simplemente use dateComponents. Por ejemplo, en Swift 3:

let components = Calendar.current.dateComponents([.month, .day, .hour, .minute, .second], from: previousDate, to: now)

O, en Swift 2.3:

let components = NSCalendar.currentCalendar().components([.Month, .Day, .Hour, .Minute, .Second], fromDate: previousDate, toDate: now, options: [])

Extension + DateComponentsFormatter combinados de la respuesta de @ leo-dabus

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"

   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;
        }

Agregué una versión "larga" a la respuesta de Leo Dabus en caso de que desee tener una cadena que diga algo así como "hace 2 semanas" en lugar de solo "2w" ...

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([.weekOfYear], from: date, to: self).weekOfYear ?? 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 ""
    }

    func offsetLong(from date: Date) -> String {
        if years(from: date)   > 0 { return years(from: date) > 1 ? "\(years(from: date)) years ago" : "\(years(from: date)) year ago" }
        if months(from: date)  > 0 { return months(from: date) > 1 ? "\(months(from: date)) months ago" : "\(months(from: date)) month ago" }
        if weeks(from: date)   > 0 { return weeks(from: date) > 1 ? "\(weeks(from: date)) weeks ago" : "\(weeks(from: date)) week ago"   }
        if days(from: date)    > 0 { return days(from: date) > 1 ? "\(days(from: date)) days ago" : "\(days(from: date)) day ago" }
        if hours(from: date)   > 0 { return hours(from: date) > 1 ? "\(hours(from: date)) hours ago" : "\(hours(from: date)) hour ago"   }
        if minutes(from: date) > 0 { return minutes(from: date) > 1 ? "\(minutes(from: date)) minutes ago" : "\(minutes(from: date)) minute ago" }
        if seconds(from: date) > 0 { return seconds(from: date) > 1 ? "\(seconds(from: date)) seconds ago" : "\(seconds(from: date)) second ago" }
        return ""
    }

}

-> Use esto para encontrar el intervalo de tiempo entre dos fechas en Swift (con dos cadenas).

func timeGapBetweenDates(previousDate : String,currentDate : String)
{
    let dateString1 = previousDate
    let dateString2 = currentDate

    let Dateformatter = DateFormatter()
    Dateformatter.dateFormat = "yyyy-MM-dd HH:mm:ss"


    let date1 = Dateformatter.date(from: dateString1)
    let date2 = Dateformatter.date(from: dateString2)


    let distanceBetweenDates: TimeInterval? = date2?.timeIntervalSince(date1!)
    let secondsInAnHour: Double = 3600
    let minsInAnHour: Double = 60
    let secondsInDays: Double = 86400
    let secondsInWeek: Double = 604800
    let secondsInMonths : Double = 2592000
    let secondsInYears : Double = 31104000

    let minBetweenDates = Int((distanceBetweenDates! / minsInAnHour))
    let hoursBetweenDates = Int((distanceBetweenDates! / secondsInAnHour))
    let daysBetweenDates = Int((distanceBetweenDates! / secondsInDays))
    let weekBetweenDates = Int((distanceBetweenDates! / secondsInWeek))
    let monthsbetweenDates = Int((distanceBetweenDates! / secondsInMonths))
    let yearbetweenDates = Int((distanceBetweenDates! / secondsInYears))
    let secbetweenDates = Int(distanceBetweenDates!)




    if yearbetweenDates > 0
    {
        print(yearbetweenDates,"years")//0 years
    }
    else if monthsbetweenDates > 0
    {
        print(monthsbetweenDates,"months")//0 months
    }
    else if weekBetweenDates > 0
    {
        print(weekBetweenDates,"weeks")//0 weeks
    }
    else if daysBetweenDates > 0
    {
        print(daysBetweenDates,"days")//5 days
    }
    else if hoursBetweenDates > 0
    {
        print(hoursBetweenDates,"hours")//120 hours
    }
    else if minBetweenDates > 0
    {
        print(minBetweenDates,"minutes")//7200 minutes
    }
    else if secbetweenDates > 0
    {
        print(secbetweenDates,"seconds")//seconds
    }
}

Código ligeramente modificado para Swift 3.0

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!

Swift 5.1 • iOS 13

Puede usar RelativeDateFormatter que Apple introdujo en iOS 13.

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

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

print(relativeDate) // 4 hours ago

Consulte Cómo mostrar una fecha y hora relativas usando RelativeDateTimeFormatter .

Si su propósito es obtener el número exacto de días entre dos fechas, puede solucionar este problema de la siguiente manera:

// 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

Con Swift 3, de acuerdo con sus necesidades, puede elegir una de las dos formas siguientes para resolver su problema.

1. Mostrar la diferencia entre dos fechas para el usuario

Puede usar a DateComponentsFormatterpara crear cadenas para la interfaz de su aplicación. DateComponentsFormattertiene una maximumUnitCountpropiedad con la siguiente declaración:

var maximumUnitCount: Int { get set }

Use esta propiedad para limitar el número de unidades que se muestran en la cadena resultante. Por ejemplo, con esta propiedad establecida en 2, en lugar de "1h 10m, 30s", la cadena resultante sería "1h 10m". Use esta propiedad cuando tenga limitaciones de espacio o desee redondear los valores a la unidad grande más cercana.

Al establecer maximumUnitCountel valor en 1, tiene la garantía de mostrar la diferencia en una sola DateComponentsFormatterunidad (años, meses, días, horas o minutos).

El siguiente código de Playground muestra cómo mostrar la diferencia entre dos fechas:

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")

Tenga en cuenta que DateComponentsFormatterredondea el resultado. Por lo tanto, una diferencia de 4 horas y 30 minutos se mostrará como 5 horas .

Si necesita repetir esta operación, puede refactorizar su código:

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. Obtenga la diferencia entre dos fechas sin formatear

Si no necesita mostrar con el formato la diferencia entre dos fechas para el usuario, puede usar Calendar. Calendartiene un método dateComponents(_:from:to:)que tiene la siguiente declaración:

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

Devuelve la diferencia entre dos fechas.

El siguiente código de Playground que se usa dateComponents(_:from:to:)muestra cómo recuperar la diferencia entre dos fechas devolviendo la diferencia en un solo tipo de Calendar.Component(años, meses, días, horas o minutos).

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
    }
}

Si necesita repetir esta operación, puede refactorizar su código:

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
}

En Swift 2.2

    /// Returns the amount of years from another date
func years(fromdate: NSDate) -> Int {
    return NSCalendar.currentCalendar().components([.Year], fromDate: fromdate, toDate: NSDate(), options: []).year ?? 0
}
/// Returns the amount of months from another date
func months(fromdate: NSDate) -> Int {
    return NSCalendar.currentCalendar().components([.Month], fromDate: fromdate, toDate: NSDate(), options: []).month ?? 0
}
/// Returns the amount of weeks from another date
func weeks(fromdate: NSDate) -> Int {
    return NSCalendar.currentCalendar().components([.WeekOfYear], fromDate: fromdate, toDate: NSDate(), options: []).weekOfYear ?? 0
}
/// Returns the amount of days from another date
func days(fromdate: NSDate) -> Int {
    return NSCalendar.currentCalendar().components([.Day], fromDate: fromdate, toDate: NSDate(), options: []).day ?? 0
}
/// Returns the amount of hours from another date
func hours(fromdate: NSDate) -> Int {
    return NSCalendar.currentCalendar().components([.Hour], fromDate: fromdate, toDate: NSDate(), options: []).hour ?? 0
}
/// Returns the amount of minutes from another date
func minutes(fromdate: NSDate) -> Int {
    return NSCalendar.currentCalendar().components([.Minute], fromDate: fromdate, toDate: NSDate(), options: []).minute ?? 0
}
/// Returns the amount of seconds from another date
func seconds(fromdate: NSDate) -> Int {
    return NSCalendar.currentCalendar().components(.Second, fromDate: fromdate, toDate: NSDate(), options: []).second ?? 0
}

Una pequeña adición a la respuesta de Leo Dabus para proporcionar las versiones en plural y ser más legible para los humanos.

Swift 3

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)   == 1 { return "\(years(from: date)) year"   } else if years(from: date)   > 1 { return "\(years(from: date)) years"   }
        if months(from: date)  == 1 { return "\(months(from: date)) month"  } else if months(from: date)  > 1 { return "\(months(from: date)) month"  }
        if weeks(from: date)   == 1 { return "\(weeks(from: date)) week"   } else if weeks(from: date)   > 1 { return "\(weeks(from: date)) weeks"   }
        if days(from: date)    == 1 { return "\(days(from: date)) day"    } else if days(from: date)    > 1 { return "\(days(from: date)) days"    }
        if hours(from: date)   == 1 { return "\(hours(from: date)) hour"   } else if hours(from: date)   > 1 { return "\(hours(from: date)) hours"   }
        if minutes(from: date) == 1 { return "\(minutes(from: date)) minute" } else if minutes(from: date) > 1 { return "\(minutes(from: date)) minutes" }
        return ""
    }
}

Esta es la versión más corta: Básicamente trato de obtener la diferencia entre la marca de tiempo de publicación con el Date()ahora.

// 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))
}

Aquí está mi respuesta para las respuestas Swift 3 anteriores. Esto es actual a partir de noviembre de 2016, la versión de Xcode fue 8.2 Beta (8C23). Utilicé algunas de las sugerencias de Sagar y Emin anteriores y, a veces, tuve que dejar que Xcode se completara automáticamente para sugerir la sintaxis. Parecía que la sintaxis realmente cambió a esta versión beta. buyDateObtuve de un 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)")

Para XCode Versión 8.3.3 y 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)")

Alguna adición en jose920405 responde para que sea compatible con Swift 3.0 y superior

func getDateTimeDiff(dateStr:String) -> String {

    let formatter : DateFormatter = DateFormatter()
    formatter.timeZone = NSTimeZone.local
    formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"

    let now = formatter.string(from: NSDate() as Date)
    let startDate = formatter.date(from: dateStr)
    let endDate = formatter.date(from: now)

    // *** create calendar object ***
    var calendar = NSCalendar.current

    // *** Get components using current Local & Timezone ***
    print(calendar.dateComponents([.year, .month, .day, .hour, .minute, .second], from: startDate!))

    // *** define calendar components to use as well Timezone to UTC ***
    let unitFlags = Set<Calendar.Component>([.year, .month, .day, .hour, .minute, .second])
    calendar.timeZone = TimeZone(identifier: "UTC")!
    let dateComponents = calendar.dateComponents(unitFlags, from: startDate!, to: endDate!)

    // *** Get Individual components from date ***
    let years = dateComponents.year!
    let months = dateComponents.month!
    let days = dateComponents.day!
    let hours = dateComponents.hour!
    let minutes = dateComponents.minute!
    let seconds = dateComponents.second!

    var timeAgo = ""

    if (seconds > 0){
        if seconds < 2 {
            timeAgo = "Second Ago"
        }
        else{
            timeAgo = "\(seconds) Second Ago"
        }
    }

    if (minutes > 0){
        if minutes < 2 {
            timeAgo = "Minute Ago"
        }
        else{
            timeAgo = "\(minutes) Minutes Ago"
        }
    }

    if(hours > 0){
        if minutes < 2 {
            timeAgo = "Hour Ago"
        }
        else{
            timeAgo = "\(hours) Hours Ago"
        }
    }

    if (days > 0) {
        if minutes < 2 {
            timeAgo = "Day Ago"
        }
        else{
            timeAgo = "\(days) Days Ago"
        }
    }

    if(months > 0){
        if minutes < 2 {
            timeAgo = "Month Ago"
        }
        else{
            timeAgo = "\(months) Months Ago"
        }
    }

    if(years > 0){
        if minutes < 2 {
            timeAgo = "Year Ago"
        }
        else{
            timeAgo = "\(years) Years Ago"
        }
    }

    DLog("timeAgo is ===> \(timeAgo)")
    return timeAgo;
}

Usa este código:

let registrationDateString = "2008-10-06 00:00:00"
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "yyyy-MM-dd hh:mm:ss"
    if let registrationDate = dateFormatter.date(from: registrationDateString) {
        let currentDate = Date()
        let dateDifference = Calendar.current.dateComponents([.day, .month, .year],
                                                               from: registrationDate,
                                                               to: currentDate)
        print("--------------------- Result: \(dateDifference.year ?? 0) years \(dateDifference.month ?? 0) months and \(dateDifference.day ?? 0) days")
    } else {
        print("--------------------- No result")
    }

La producción es: Resultado: 10 años 1 mes y 18 días

import Foundation

extension DateComponents {

    func dateComponentsToTimeString() -> String {

        var hour = "\(self.hour!)"
        var minute = "\(self.minute!)"
        var second = "\(self.second!)"

        if self.hour! < 10 { hour = "0" + hour }
        if self.minute! < 10 { minute = "0" + minute }
        if self.second! < 10 { second = "0" + second }

        let str = "\(hour):\(minute):\(second)"
        return str
    }

}

extension Date {

    func offset(from date: Date)-> DateComponents {
        let components = Set<Calendar.Component>([.second, .minute, .hour, .day, .month, .year])
        let differenceOfDate = Calendar.current.dateComponents(components, from: date, to: self)
        return differenceOfDate
    }
}

Utilizar:

var durationString: String {
        return self.endTime.offset(from: self.startTime).dateComponentsToTimeString()
    }