Ios Swift中的DateComponents返回奇怪的值。为什么？

我在计算两次约会的时差。我有一段代码：

func timeAgoSinceDate(_ date:Date, numericDates:Bool) -> String {
    let calendar = Calendar.current
    let now = Date()
    let components:DateComponents = (calendar as NSCalendar).components([NSCalendar.Unit.minute , NSCalendar.Unit.hour , NSCalendar.Unit.day , NSCalendar.Unit.weekOfYear , NSCalendar.Unit.month , NSCalendar.Unit.year , NSCalendar.Unit.second], from: now, to: date, options: NSCalendar.Options())
    print(now)
    print(date)
    print(components.month)

以下是我在控制台中看到的一些示例：

2016-10-29 16:12:34 +0000
2017-03-29 16:03:13 +0000
Optional(4) //I think it should return 5?


2016-10-29 16:12:34 +0000
2017-01-29 17:03:13 +0000
Optional(2) //again, why 2 instead of 3?

2016-10-29 16:12:34 +0000
2015-09-30 15:54:20 +0000
Optional(0) //why 0 since it's almost whole year?


2016-10-29 16:12:34 +0000
2016-05-29 14:09:31 +0000
Optional(-5) //this seems to be fine

等等。。。这里有什么问题

我的问题是日期的计算。在我的代码中，我正在做：

if (components.month! >= 2) {
        return "in \(components.month!) months"
    } else if (components.month! >= 1){
        if (numericDates){
            return "in 1 month"
        } else {
            return "in one month"
        }
    }

    else if (components.month! <= -2) {
        return "\(components.month!) months ago"
    } else if (components.month! <= -1){
        if (numericDates){
            return "1 month ago"
        } else {
            return "one month ago"
        }
    }

但在现实生活中，它应该返回3，因为它是10月和1月之间的差值。有没有更好的方法来计算这种差异，而不是用一堆将所有内容取整的

if

语句

2016-10-29 16:12:34 +0000
2017-03-29 16:03:13 +0000
Optional(4) //I think it should return 5?

由于16:03小于16:12，您需要再加9分21秒，它才会返回5

2016-10-29 16:12:34 +0000
2017-01-29 17:03:13 +0000
Optional(2) //again, why 2 instead of 3?

夏令时为2016年11月6日。你损失了一个小时。我很确定这就是为什么它认为只有两个月的时间

加上一小时：

2016-10-29 16:12:34 +0000
2017-01-29 18:03:13 +0000
Optional(3)

你得到'3'

更改月份，但保留原来的小时数：

2016-7-29 16:12:34 +0000
2016-10-29 17:03:13 +0000
Optional(3)

你也会得到“3”

2016-10-29 16:12:34 +0000
2015-09-30 15:54:20 +0000
Optional(0) //why 0 since it's almost whole year?

日期组件返回组件定义中包含的最高单位的差值。在您的例子中，您已经包括了

NSCalendar.Unit.year

。因此，

components.month

将返回月份单位，而不是月份的总差值。因此，此计算中的月份单位为0个月。如果在一个日期上加上25年零5个月，它将返回“5”。但是，如果要删除

NSCalendar.Unit.year

，则它将使用月作为最高单位，并返回“305”

您可以像这样测试某些日期：

let startString = "2016-7-30 16:12:34 +0000"
let endString = "2016-10-30 17:03:13 +0000"

let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd HH:mm:ss Z"
let now = formatter.date(from: startString)!
let date = formatter.date(from: endString)!

---

从2016-10-29 16:12:34到2017-03-29 16:03:13，一共有4个月28天23小时50分39秒 这就是为什么在第一个示例中，

components.month

的计算结果为

4

如果您打算计算与2016年10月的差额（以月为单位） 到2017年3月，您必须计算 两个日期的月份开始日期：

let startOfFirstMonth = calendar.date(from: calendar.dateComponents([.year, .month], from: firstDate))!
let startOfSecondMonth = calendar.date(from: calendar.dateComponents([.year, .month], from: secondDate))!

let comps = calendar.dateComponents([.month], from: startOfFirstMonth, to: startOfSecondMonth)
print(comps.month)

---

此答案旨在作为Frankie答案的补充信息

func calendarTest(_ from: String, _ to: String) {
    var calendar = Calendar.current
    calendar.timeZone = TimeZone(identifier: "Europe/Paris")! //<- GMT+1
    let inFormatter = DateFormatter()
    inFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
    inFormatter.timeZone = TimeZone(abbreviation: "UTC")!
    guard
        let now = inFormatter.date(from: from),
        let date = inFormatter.date(from: to)
    else {return}
    //Removing "weeks" for clarity
    let components = (calendar as NSCalendar).components([.minute, .hour, .day/*, .weekOfYear*/, .month, .year, .second], from: now, to: date, options: [])
    let outFormatter = DateFormatter()
    outFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
    outFormatter.timeZone = calendar.timeZone
    print("UTC time                  Localtime")
    print(now, outFormatter.string(from: now))
    print(date, outFormatter.string(from: date))
    print(components)
}

输出：

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-03-29 16:03:13 +0000 2017-03-29 18:03:13
year: 0 month: 4 day: 28 hour: 23 minute: 50 second: 39 isLeapMonth: false 
UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-03-29 16:12:34 +0000 2017-03-29 18:12:34
year: 0 month: 5 day: 0 hour: 0 minute: 0 second: 0 isLeapMonth: false 

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-01-29 17:03:13 +0000 2017-01-29 18:03:13
year: 0 month: 2 day: 30 hour: 23 minute: 50 second: 39 isLeapMonth: false 
UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-01-29 17:12:34 +0000 2017-01-29 18:12:34
year: 0 month: 3 day: 0 hour: 0 minute: 0 second: 0 isLeapMonth: false 

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2015-09-30 15:54:20 +0000 2015-09-30 17:54:20
year: -1 month: 0 day: -29 hour: 0 minute: -18 second: -14 isLeapMonth: false 

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2016-05-29 14:09:31 +0000 2016-05-29 16:09:31
year: 0 month: -5 day: 0 hour: -2 minute: -3 second: -3 isLeapMonth: false 

---

输出：

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-03-29 16:03:13 +0000 2017-03-29 18:03:13
year: 0 month: 4 day: 28 hour: 23 minute: 50 second: 39 isLeapMonth: false 
UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-03-29 16:12:34 +0000 2017-03-29 18:12:34
year: 0 month: 5 day: 0 hour: 0 minute: 0 second: 0 isLeapMonth: false 

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-01-29 17:03:13 +0000 2017-01-29 18:03:13
year: 0 month: 2 day: 30 hour: 23 minute: 50 second: 39 isLeapMonth: false 
UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-01-29 17:12:34 +0000 2017-01-29 18:12:34
year: 0 month: 3 day: 0 hour: 0 minute: 0 second: 0 isLeapMonth: false 

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2015-09-30 15:54:20 +0000 2015-09-30 17:54:20
year: -1 month: 0 day: -29 hour: 0 minute: -18 second: -14 isLeapMonth: false 

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2016-05-29 14:09:31 +0000 2016-05-29 16:09:31
year: 0 month: -5 day: 0 hour: -2 minute: -3 second: -3 isLeapMonth: false 

---

输出：

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-03-29 16:03:13 +0000 2017-03-29 18:03:13
year: 0 month: 4 day: 28 hour: 23 minute: 50 second: 39 isLeapMonth: false 
UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-03-29 16:12:34 +0000 2017-03-29 18:12:34
year: 0 month: 5 day: 0 hour: 0 minute: 0 second: 0 isLeapMonth: false 

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-01-29 17:03:13 +0000 2017-01-29 18:03:13
year: 0 month: 2 day: 30 hour: 23 minute: 50 second: 39 isLeapMonth: false 
UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-01-29 17:12:34 +0000 2017-01-29 18:12:34
year: 0 month: 3 day: 0 hour: 0 minute: 0 second: 0 isLeapMonth: false 

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2015-09-30 15:54:20 +0000 2015-09-30 17:54:20
year: -1 month: 0 day: -29 hour: 0 minute: -18 second: -14 isLeapMonth: false 

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2016-05-29 14:09:31 +0000 2016-05-29 16:09:31
year: 0 month: -5 day: 0 hour: -2 minute: -3 second: -3 isLeapMonth: false 

---

输出：

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-03-29 16:03:13 +0000 2017-03-29 18:03:13
year: 0 month: 4 day: 28 hour: 23 minute: 50 second: 39 isLeapMonth: false 
UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-03-29 16:12:34 +0000 2017-03-29 18:12:34
year: 0 month: 5 day: 0 hour: 0 minute: 0 second: 0 isLeapMonth: false 

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-01-29 17:03:13 +0000 2017-01-29 18:03:13
year: 0 month: 2 day: 30 hour: 23 minute: 50 second: 39 isLeapMonth: false 
UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2017-01-29 17:12:34 +0000 2017-01-29 18:12:34
year: 0 month: 3 day: 0 hour: 0 minute: 0 second: 0 isLeapMonth: false 

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2015-09-30 15:54:20 +0000 2015-09-30 17:54:20
year: -1 month: 0 day: -29 hour: 0 minute: -18 second: -14 isLeapMonth: false 

UTC time                  Localtime
2016-10-29 16:12:34 +0000 2016-10-29 18:12:34
2016-05-29 14:09:31 +0000 2016-05-29 16:09:31
year: 0 month: -5 day: 0 hour: -2 minute: -3 second: -3 isLeapMonth: false 

请记住

日历。当前
使用本地时区的日期和时间计算月份


顺便说一下，在获取两个
日期
之间的
日期组件时，无需使用
NSCalendar

let components = calendar.dateComponents([.minute, .hour, .day/*, .weekOfYear*/,.month, .year, .second], from: now, to: date)

你在哪个时区？日期以UTC/GMT格式打印，但日历计算是在本地日历/时区中完成的。在第一个示例中，给定日期之间的间隔不到5个月，因此结果4是正确的。嗯，但我认为时区不应影响
月
情况下的计算。。。不管怎样，我在
GMT+1
，有没有办法独立于时区进行计算？你可以将日历时区设置为GMT，但即使这样，在第一个示例中，你也会得到4而不是5，在第三个示例中，会得到0，因为相差不到一年。尝试
打印（组件）
以查看实际差异。几乎在编程方面不是；-）我不同意第一种说法，因为如果你评估“从2016-10-29到2017-03-29”，而不使用HH:mm:ss，那么它实际上评估为5个月。但是OP的例子包括了精确的时间，这使得它只差5个月。（顺便说一句，这不是我的反对票）@Frankie：你说得对，那太简短了，我现在已经解决了，谢谢你的反馈然而，建议的解决方案应该适用于问题的所有情况（我从更新中了解到）。