如何在Objective-C中生成随机日期？

Question

我想要生成两个日期之间的随机日期--例如从今天到未来60天之间的一个随机日期。我该如何做到？

更新

根据答案提供的信息，我想出了这个方法，我经常使用：

// Generate a random date sometime between now and n days before day.
// Also, generate a random time to go with the day while we are at it.
- (NSDate *) generateRandomDateWithinDaysBeforeToday:(NSInteger)days
{
    int r1 = arc4random_uniform(days);
    int r2 = arc4random_uniform(23);
    int r3 = arc4random_uniform(59);

    NSDate *today = [NSDate new];
    NSCalendar *gregorian = 
             [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

    NSDateComponents *offsetComponents = [NSDateComponents new];
    [offsetComponents setDay:(r1*-1)];
    [offsetComponents setHour:r2];
    [offsetComponents setMinute:r3];

    NSDate *rndDate1 = [gregorian dateByAddingComponents:offsetComponents 
                                                  toDate:today options:0];

    return rndDate1;
}

- memmons

---

可能是在iPhone上循环两个NSDates的最简单方法？的重复问题。 - jscs

我不知道你在想什么，@lulius Cæsar，但这个问题与在两个日期之间循环根本没有任何相似之处... - memmons

同样的代码，重构并进行了文档记录 https://gist.github.com/eirnym/c9526a045556e4d8464b41a367843e3c - Eir Nym

Answer 1

获取一个随机数并将其用作时间间隔，然后将其添加到起始日期。例如：

NSTimeInterval timeBetweenDates = [endDate timeIntervalSinceDate:startDate];
NSTimeInterval randomInterval = ((NSTimeInterval)arc4random() / ARC4RANDOM_MAX) * timeBetweenDates;

NSDate *randomDate = [startDate dateByAddingTimeInterval:randomInterval];

- Tommy

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如果您遇到有关ARC4RANDOM_MAX的错误，请将其替换为0x100000000或使用#define ARC4RANDOM_MAX 0x100000000。 - budiDino

顺便说一句，我认为这应该成为被接受的答案，因为它解决了比被接受的答案更多的随机日期用例。 - budiDino

Answer 2

1. Generate a random number between 1 and 60

   int r = arc4random_uniform(60) + 1;
   
   // Usage : arc4random_uniform(hi - lo + 1) + lo
   

2. Get current date

   [NSDate date];
   

3. Use NSDateComponents to subtract the random number from your days component and generate a new date.

- Legolas

---

在这里可能不是什么大问题，但使用百分号（%）几乎总是会对随机数产生偏差。你需要使用的函数是arc4random_uniform()。 - Rob Napier

arc4random_uniform(upper_bound) 返回一个大于等于0且小于upper_bound的整数，使得分布是均匀的。也就是说，范围内的所有值都有同样的可能性。 - Rob Napier

@RobNapier: 感谢您启发我 :) - Legolas

非常有用的信息。谢谢！我之前不知道如何解决这个问题。现在，我不仅有了一个好的解决方案，而且还学到了一些关于随机数生成的知识！arc4random()的非均匀分布（在创建BOOL时特别糟糕）一直让我感到困扰。 - memmons

Answer 3

这是一个适用于Swift 4.x的扩展，它允许您指定一段时间（以天为单位），然后使用它来查找当前日期之前或之后的随机Date。

extension Date {
    static func randomDate(range: Int) -> Date {
        // Get the interval for the current date
        let interval =  Date().timeIntervalSince1970
        // There are 86,400 milliseconds in a day (ignoring leap dates)
        // Multiply the 86,400 milliseconds against the valid range of days
        let intervalRange = Double(86_400 * range)
        // Select a random point within the interval range
        let random = Double(arc4random_uniform(UInt32(intervalRange)) + 1)
        // Since this can either be in the past or future, we shift the range
        // so that the halfway point is the present
        let newInterval = interval + (random - (intervalRange / 2.0))
        // Initialize a date value with our newly created interval
        return Date(timeIntervalSince1970: newInterval)
    }
}

你这样称呼它：

Date.randomDate(range: 500) // Any date that is +/- 500 days from the current date

运行这个程序10次会产生：

2019-03-15 01:45:52 +0000
2018-12-20 02:09:51 +0000
2018-06-28 10:28:31 +0000
2018-08-02 08:13:01 +0000
2019-01-25 07:04:18 +0000
2018-08-30 22:37:52 +0000
2018-10-05 19:38:22 +0000
2018-11-30 04:51:18 +0000
2019-03-24 07:27:39 +0000

- CodeBender

Answer 4

这个框架在生成随机日期方面做得很好。但是在Swift中： https://github.com/thellimist/SwiftRandom/blob/master/SwiftRandom/Randoms.swift

public extension NSDate {
    /// SwiftRandom extension
    public static func randomWithinDaysBeforeToday(days: Int) -> NSDate {
        let today = NSDate()

        guard let gregorian = NSCalendar(calendarIdentifier: NSCalendarIdentifierGregorian) else {
            print("no calendar \"NSCalendarIdentifierGregorian\" found")
            return today
        }

        let r1 = arc4random_uniform(UInt32(days))
        let r2 = arc4random_uniform(UInt32(23))
        let r3 = arc4random_uniform(UInt32(23))
        let r4 = arc4random_uniform(UInt32(23))

        let offsetComponents = NSDateComponents()
        offsetComponents.day = Int(r1) * -1
        offsetComponents.hour = Int(r2)
        offsetComponents.minute = Int(r3)
        offsetComponents.second = Int(r4)

        guard let rndDate1 = gregorian.dateByAddingComponents(offsetComponents, toDate: today, options: []) else {
            print("randoming failed")
            return today
        }
        return rndDate1
    }

    /// SwiftRandom extension
    public static func random() -> NSDate {
        let randomTime = NSTimeInterval(arc4random_uniform(UInt32.max))
        return NSDate(timeIntervalSince1970: randomTime)
    }

}

- Esqarrouth

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不错的扩展！r3和r4随机数应该随机到59吗？ - Felipe Ferri

嗯，是的 :D 欢迎在 GitHub 上发送拉取请求。 - Esqarrouth

好的，拉取请求已发送。顺便说一下，SwiftRandom非常有用，感谢您的建议！您是作者吗？ - Felipe Ferri

链接失效！@Esqarrouth - Hemang

Answer 5

使用秒。伪代码如下：

1 Generate a random integer between 0 and (60 * 60 * 24 * 60)
2 Get the unixtime in seconds for the current time
3 Add your random integer
4 Convert this integer back to a date

- Albert Veli

---

一天的长度可能比24小时长或短，这是由于夏令时的开始和结束所致。 - Ken Thomases

啊，是的，那是正确的。这个方法将在60天的范围内产生一个随机日期，加减一个小时，这在大多数情况下都是可以接受的。 - Albert Veli

Answer 6

Swift 3.x +

public extension Date {
    /// SwiftRandom extension
    public static func randomWithinDaysBeforeToday(days: Int) -> Date {
        let today = Date()
        let gregorian = Calendar(identifier: .gregorian)

        let r1 = arc4random_uniform(UInt32(days))
        let r2 = arc4random_uniform(UInt32(23))
        let r3 = arc4random_uniform(UInt32(23))
        let r4 = arc4random_uniform(UInt32(23))

        let offsetComponents = NSDateComponents()
        offsetComponents.day = Int(r1) * -1
        offsetComponents.hour = Int(r2)
        offsetComponents.minute = Int(r3)
        offsetComponents.second = Int(r4)

        let rndDate1 = gregorian.date(byAdding: offsetComponents as DateComponents, to: today)
        return rndDate1!
    }

    /// SwiftRandom extension
    public static func random() -> Date {
        let randomTime = TimeInterval(arc4random_uniform(UInt32.max))
        return Date(timeIntervalSince1970: randomTime)
    }
}

_{附言：Esqarrouth的答案已经修正为最新的Swift。}

- Hemang