如何在Swift中使用NSDate计算特定日期

Question

我正在swift开发ios应用，并且我有一个带有7个选项的滑块。 每个选项代表特定的日期。

到目前为止，我的代码如下：

func convertValueToDate(value: Float) -> NSDate{

    var currentDate:NSDate = NSDate()

    switch(value){
    case 1:
        print("5 years ago")
        return NSDate()
    case 2:
        print("one year ago")
        return NSDate()
    case 3:
        print("six months ago")
        return NSDate()
    case 4:
        print("one month ago")
        return NSDate()
    case 5:
        print("one week ago")
        return NSDate()
    case 6:
        print("yesterday")
        return NSDate()
    case 7:
        print("today")
        return NSDate()
    default:
        print("default date")
        return NSDate()
    }
}

如您在上方看到的-我在控制台中打印了要返回的内容。 但是我不想打印，而是以NSDate格式返回这些日期。 我不知道如何计算每个选项的时间，因为我想每天有0:00:01 AM 。 因此，例如。 当用户输入数字7我想将昨天0:00:01 AM的确切日期返回给他。 当用户选择数字5我想给他一个星期前的日期，时间为0:00:01 AM ，依此类推。 我该如何计算它，以便该函数始终向我返回0:00:01 AM和计算出的日期？

Answer 1

您可以使用NSCalendar方法dateByAddingUnit：

func convertValueToDate(value: Float) -> NSDate {
    struct Cal {
        static let iso8601 = NSCalendar(identifier: NSCalendarIdentifierISO8601)!
    }
    let now = NSDate()
    print("now: ", now)
    switch(value) {
    case 1:
        print("5 years ago")
        return Cal.iso8601.dateByAddingUnit(.Year, value: -5, toDate: now, options: [])!
    case 2:
        print("one year ago")
        return Cal.iso8601.dateByAddingUnit(.Year, value: -1, toDate: now, options: [])!
    case 3:
        print("six months ago")
        return Cal.iso8601.dateByAddingUnit(.Month, value: -6, toDate: now, options: [])!
    case 4:
        print("one month ago")
        return Cal.iso8601.dateByAddingUnit(.Month, value: -1, toDate: now, options: [])!
    case 5:
        print("one week ago")
        return Cal.iso8601.dateByAddingUnit(.WeekOfYear, value: -1, toDate: now, options: [])!
    case 6:
        print("yesterday")
        return Cal.iso8601.dateByAddingUnit(.Day, value: -1, toDate: now, options: [])!
    case 7:
        print("today")
        return now
    default:
        print("default date")
        return now
    }
}

如果您需要返回当天的开始日期，则可以使用NSCalendar startOfDayForDate方法。

func convertValueToDate(value: Float) -> NSDate {
    struct Cal {
        static let iso8601 = NSCalendar(identifier: NSCalendarIdentifierISO8601)!
    }
    let now = NSDate()
    print("now: ", now)
    let result: NSDate
    switch(value) {
    case 1:
        print("5 years ago")
        result = Cal.iso8601.dateByAddingUnit(.Year, value: -5, toDate: now, options: [])!
    case 2:
        print("one year ago")
        result =  Cal.iso8601.dateByAddingUnit(.Year, value: -1, toDate: now, options: [])!
    case 3:
        print("six months ago")
        result =  Cal.iso8601.dateByAddingUnit(.Month, value: -6, toDate: now, options: [])!
    case 4:
        print("one month ago")
        result =  Cal.iso8601.dateByAddingUnit(.Month, value: -1, toDate: now, options: [])!
    case 5:
        print("one week ago")
        result =  Cal.iso8601.dateByAddingUnit(.WeekOfYear, value: -1, toDate: now, options: [])!
    case 6:
        print("yesterday")
        result =  Cal.iso8601.dateByAddingUnit(.Day, value: -1, toDate: now, options: [])!
    case 7:
        print("today")
        result = now
    default:
        print("default date")
        result = now
    }
    return Cal.iso8601.startOfDayForDate(result)
}

Answer 2

这是Swift 3中的解决方案，因为它已经在这里（对于Swift 2.x，在类之前添加NS前缀应该可以解决问题）：

import Foundation

func convertValueToDate(value: Float) -> Date{

    let calendar = Calendar.current
    let currentDate = calendar.date(bySettingHour: 00, minute: 00, second: 01, of: Date())!

    func dateByAdding(_ value: Int, _ component: Calendar.Component) -> Date {
        return calendar.date(byAdding: component, value: value, to: currentDate)!
    }

    switch(value){
    case 1:
        print("5 years ago")
        return dateByAdding(-5, .year)
    case 2:
        print("one year ago")
        return dateByAdding(-1, .year)
    case 3:
        print("six months ago")
        return dateByAdding(-6, .month)
    case 4:
        print("one month ago")
        return dateByAdding(-1, .month)
    case 5:
        print("one week ago")
        return dateByAdding(-7, .day)
    case 6:
        print("yesterday")
        return dateByAdding(-1, .day)
    case 7:
        print("today")
        return currentDate
    default:
        print("default date")
        return currentDate
    }
}