ios 从当前日期减去 7 天

Subtract 7 days from current date

提问by Alex Tau

It seems that I can't subtract 7 days from the current date. This is how i am doing it:

似乎我不能从当前日期中减去 7 天。这就是我的做法：

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *offsetComponents = [[NSDateComponents alloc] init];
[offsetComponents setDay:-7];
NSDate *sevenDaysAgo = [gregorian dateByAddingComponents:offsetComponents toDate:[NSDate date] options:0];

SevenDaysAgo gets the same value as the current date.

SevenDaysAgo 获得与当前日期相同的值。

Please help.

请帮忙。

EDIT: In my code I forgot to replace the variable which gets the current date with the right one. So above code is functional.

编辑：在我的代码中，我忘记用正确的日期替换获取当前日期的变量。所以上面的代码是功能性的。

采纳答案by Novarg

use dateByAddingTimeInterval method:

使用 dateByAddingTimeInterval 方法：

NSDate *now = [NSDate date];
NSDate *sevenDaysAgo = [now dateByAddingTimeInterval:-7*24*60*60];
NSLog(@"7 days ago: %@", sevenDaysAgo);

output:

输出：

7 days ago: 2012-04-11 11:35:38 +0000

Hope it helps

希望能帮助到你

回答by dymv

code:

代码：

NSDate *currentDate = [NSDate date];
NSDateComponents *dateComponents = [[NSDateComponents alloc] init];
[dateComponents setDay:-7];
NSDate *sevenDaysAgo = [[NSCalendar currentCalendar] dateByAddingComponents:dateComponents toDate:currentDate options:0];
NSLog(@"\ncurrentDate: %@\nseven days ago: %@", currentDate, sevenDaysAgo);
[dateComponents release];

output:

输出：

currentDate: 2012-04-22 12:53:45 +0000
seven days ago: 2012-04-15 12:53:45 +0000

And I'm fully agree with JeremyP.

我完全同意 JeremyP。

BR.
Eugene

BR。
尤金

回答by Dov

If you're running at least iOS 8 or OS X 10.9, there's an even cleaner way:

如果您至少运行 iOS 8 或 OS X 10.9，还有更简洁的方法：

NSDate *sevenDaysAgo = [[NSCalendar currentCalendar] dateByAddingUnit:NSCalendarUnitDay
                                                                value:-7
                                                               toDate:[NSDate date]
                                                              options:0];

Or, with Swift 2:

或者，使用 Swift 2：

let sevenDaysAgo = NSCalendar.currentCalendar().dateByAddingUnit(.Day, value: -7,
    toDate: NSDate(), options: NSCalendarOptions(rawValue: 0))

And with Swift 3 and up it gets even more compact:

使用 Swift 3 及更高版本，它变得更加紧凑：

let sevenDaysAgo = Calendar.current.date(byAdding: .day, value: -7, to: Date())

回答by Marckaraujo

Swift 3

斯威夫特 3

Calendar.current.date(byAdding: .day, value: -7, to: Date())

回答by Mark Moeykens

Swift 4.2 - Mutate (Update) Self

Swift 4.2 - 变异（更新）自我

Here is another way the original poster can get one week ago if he already has a date variable (updates/mutates itself).

如果原始发布者已经有一个日期变量（更新/变异本身），那么这是一周前原始发布者可以获得的另一种方式。

extension Date {
    mutating func changeDays(by days: Int) {
        self = Calendar.current.date(byAdding: .day, value: days, to: self)!
    }
}

Usage

用法

var myDate = Date()       // Jan 08, 2019
myDate.changeDays(by: 7)  // Jan 15, 2019
myDate.changeDays(by: 7)  // Jan 22, 2019
myDate.changeDays(by: -1) // Jan 21, 2019

or

或者

// Iterate through one week
for i in 1...7 {
    myDate.changeDays(by: i)
    // Do something
}

回答by user3069232

Swift 4.2iOS 11.x Babec'ssolution, pure Swift

Swift 4.2iOS 11.x Babec 的解决方案，纯 Swift

extension Date {
  static func changeDaysBy(days : Int) -> Date {
    let currentDate = Date()
    var dateComponents = DateComponents()
    dateComponents.day = days
    return Calendar.current.date(byAdding: dateComponents, to: currentDate)!
  }
}

回答by Babac

dymv's answer work great. This you can use in swift

dymv 的回答很好。这你可以在 swift 中使用

extension NSDate {    
    static func changeDaysBy(days : Int) -> NSDate {
        let currentDate = NSDate()
        let dateComponents = NSDateComponents()
        dateComponents.day = days
        return NSCalendar.currentCalendar().dateByAddingComponents(dateComponents, toDate: currentDate, options: NSCalendarOptions(rawValue: 0))!
    }
}

You can call this with

你可以用

NSDate.changeDaysBy(-7) // Date week earlier
NSDate.changeDaysBy(14) // Date in next two weeks

Hope it helps and thx to dymv

希望它对 dymv 有所帮助和感谢

回答by originalmyth

Swift 3.0+ version of the original accepted answer

原始接受答案的 Swift 3.0+ 版本

Date().addingTimeInterval(-7 * 24 * 60 * 60)

日期().addingTimeInterval(-7 * 24 * 60 * 60)

However, this uses absolute values only. Use calendar answers is probably more suitable in most cases.

但是，这仅使用绝对值。在大多数情况下，使用日历答案可能更合适。

回答by Sam

Using operator extension:

使用运算符扩展：

extension Date {

    static func -(lhs: Date, rhs: Int) -> Date {
        return Calendar.current.date(byAdding: .day, value: -rhs, to: lhs)!
    }
}

Usage

用法

let today = Date()
let yesterday = today - 7

回答by A.G

Swift 3:

斯威夫特 3：

A modification to Dov's answer.

对 Dov 答案的修改。

extension Date {

    func dateBeforeOrAfterFromToday(numberOfDays :Int?) -> Date {

        let resultDate = Calendar.current.date(byAdding: .day, value: numberOfDays!, to: Date())!
        return resultDate
    }
}

Usage:

用法：

let dateBefore =  Date().dateBeforeOrAfterFromToday(numberOfDays : -7)
let dateAfter = Date().dateBeforeOrAfterFromToday(numberOfDays : 7)
print ("dateBefore : \(dateBefore), dateAfter :\(dateAfter)")