NSDate swift的日期字符串

问题描述：

我正在使用日期字符串填充数组，我想查看该日期字符串并检查日期是今天还是昨天。日期字符串可能如下所示：

i'm having an array fill with date string, which i would like to go through and check whether the date is today or yesterday. The date string could look like following:

2015-04-10 22:07:00

到目前为止，我已经尝试过使用dateFormatter转换它，但它一直返回nil

So far i've tried just to convert it using dateFormatter, but it keeps returning nil

    var dateString = arrayNews[0][0].date as NSString
    var dateFormatter = NSDateFormatter()
    dateFormatter.dateFormat = "yyyy-MM-dd hh:mm:ss"

    var date = dateFormatter.dateFromString(dateString as String)
    println(date)

sudo代码我想看起来像这样

the sudo code i would like to look something like this

if dateString == currentDate
    date = "Today, hh:mm"
else if dateString == currentDate(-1)
    date = "Yesterday, hh:mm
else
    date = dd. MM, hh:mm

在else语句中日期可能为1. April ，12：00

in the else statement the date could be 1. April, 12:00

我如何实现这样的逻辑？

How can i achieve such a logic?

没有逻辑

func getDate(dateStr:String, format:String = "yyyy-MM-dd HH:mm:ss") -> NSString {
    var dateFmt = NSDateFormatter()
    dateFmt.timeZone = NSTimeZone.defaultTimeZone()
    dateFmt.dateFormat = format
    let newsDate = dateFmt.dateFromString(dateStr)!

    let date = NSDate();
    let dateFormatter = NSDateFormatter()


    dateFormatter.timeZone = NSTimeZone()
    let localDate = dateFormatter.stringFromDate(date)


    return ""
}

答

你必须使用 yyyy-MM-dd HH：mm：ss 而不是 yyyy-MM-dd hh：mm：ss

HH：24h格式

hh：12h格式（带AM / PM）

使用dateFormatter注意，默认情况下，它使用localtime zone。
println（）显示GMT时间的值，由NSDate持有。

Pay attention with dateFormatter, by default, it use localtime zone. println() shows the value for GMT time, which is hold by NSDate.

这意味着，在不指定时区的情况下，当您将字符串 2015-04-10 22:07:00 转换为NSDatetime时，它会返回一个数据，即您当地时区的时间是 2015-04-10 22:07:00 。由于 NSDate 在GMT中保存日期时间，当您使用 NSDate 的值时，您将看到不同的值code>的println（）。

It means, without specifying timezone, when you convert your string 2015-04-10 22:07:00 to NSDatetime, it return a data which is the time at your local time zone is 2015-04-10 22:07:00. As NSDate holds date time in GMT, you will see a different value when you show the value of that NSDate with println().

如果你的时区是格林尼治标准时间+2（早于格林尼治标准时间2小时），当你的位置是22h：07时，格林尼治标准时间是20小时：07。当你在 NSDate 上调用 println（）时，你会看到2015-04-10 20:07:00

If your timezone is GMT+2 (2h earlier than GMT), when it's 22h:07 in your place, the GMT time is 20h:07. When you call println() on that NSDate, you see 2015-04-10 20:07:00

比较2 NSDate：

To compare 2 NSDate:

let calendar = NSCalendar(identifier: NSCalendarIdentifierGregorian)

let compareResult = calendar?.compareDate(date, toDate: date2, toUnitGranularity: NSCalendarUnit.CalendarUnitDay)

if (compareResult == NSComparisonResult.OrderedSame) {
    println("yes")
} else {
    println("no")
}

//昨天使用NSCalendar获取：

//to get yesterday, using NSCalendar:

let yesterday = calendar?.dateByAddingUnit(NSCalendarUnit.CalendarUnitDay, value: -1, toDate: date, options: NSCalendarOptions.MatchStrictly)

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