iOS＋Swiftでつかえる、TwitterやFacebookのような現在からの経過時間を計算するライブラリを作りました。「1sec,2minutes,3hours,4days」と表示するアレです。下記のコードをコピペするだけの超絶使い易い形で提供させていただきます。

ソース

TimeInterval+NSDate.swift

import UIKit

extension NSDate {
    func stringForTimeIntervalSinceCreated() -> String {
        return stringForTimeIntervalSinceCreated(nowDate:NSDate())

<pre><code>}

func stringForTimeIntervalSinceCreated(#nowDate:NSDate) -&gt; String {
    var MinInterval  :Int = 0
    var HourInterval :Int = 0
    var DayInterval  :Int = 0
    var DayModules   :Int = 0
    let interval = abs(Int(self.timeIntervalSinceDate(nowDate)))
    if (interval &gt;= 86400) {
        DayInterval = interval/86400
        DayModules = interval%86400
        if (DayModules != 0) {
            if (DayModules&gt;=3600) {
                //HourInterval=DayModules/3600;
                return String(DayInterval) + " days"
            } else {
                if (DayModules &gt;= 60) {
                    //MinInterval=DayModules/60;
                    return String(DayInterval) + " days"
                } else {
                    return String(DayInterval) + " days"
                }
            }
        } else {
            return String(DayInterval) + " days"
        }
    } else {
        if (interval &gt;= 3600) {
            HourInterval = interval/3600
            return String(HourInterval) + " hours"
        } else if (interval &gt;= 60) {
            MinInterval = interval/60
            return String(MinInterval) + " minutes"
        } else {
            return String(interval) + " sec"
        }
    }
}
</code></pre>

}

extension NSDate {
    func toString(#format:String, localeIdentifier:String = "ja_JP") -> String? {
        let formatter = NSDateFormatter()
        formatter.dateFormat = format
        formatter.locale = NSLocale(localeIdentifier: localeIdentifier)
        let dateStr = formatter.stringFromDate(self)
        return dateStr
    }
}

extension String {
    func toDate(#format:String, localeIdentifier:String = "ja_JP") -> NSDate? {
        let formatter = NSDateFormatter()
        formatter.dateFormat = format
        formatter.locale = NSLocale(localeIdentifier: localeIdentifier)
        let date = formatter.dateFromString(self)
        return date
    }
}

githubにも置いておきます。
https://github.com/hayakawatomoaki/TimeInterval

使い方１

if let createdDate = "2015-02-01 14:54:09".toDate(format: "yyyy-M-d HH:mm:ss") {
    let a = createdDate.stringForTimeIntervalSinceCreated() // non optional
    println(a) // "5 days"
}

使い方２

var createdDate = "2015-02-06 14:54:09".toDate(format: "yyyy-M-d HH:mm:ss")
var b = createdDate?.stringForTimeIntervalSinceCreated() // optional
println(b) // Optional("4 hours")

使い方３

var c = "2015-02-06 19:48:31".toDate(format: "yyyy-M-d HH:mm:ss")?.stringForTimeIntervalSinceCreated() // optional
println(c) // Optional("5 days")

Qiitaにも載せておきます。
http://qiita.com/hayakawatomoaki/items/8f1d5aeb74ba2156245c

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