时间日期

NSDate

在Objective-C中，可以使用如下的代码创建一个UTC的时间：

NSDate *currentUTCDate = [NSDate date]

但是在Swift中，如果使用如下方式：

let date = NSDate()

获取到的会是本地时间。

UTC时间与本地化时间

import UIKit

let date = NSDate();
// "Apr 1,2015,8:53 AM" <-- local without seconds

var formatter = NSDateFormatter();
formatter.dateFormat = "yyyy-MM-dd HH:mm:ss ZZZ";
let defaultTimeZoneStr = formatter.stringFromDate(date);
// "2015-04-01 08:52:00 -0400" <-- same date,local,but with seconds
formatter.timeZone = NSTimeZone(abbreviation: "UTC");
let utcTimeZoneStr = formatter.stringFromDate(date);
// "2015-04-01 12:52:00 +0000" <-- same date,now in UTC

时间比较

如果需要比较两个日期，可以使用如下方法，在如下代码中已经展示了如何处理不同的返回结果：

// Date comparision to compare current date and end date.
var dateComparisionResult:NSComparisonResult = NSDate().compare(endDate)

if dateComparisionResult == NSComparisonResult.OrderedAscending
{
    // Current date is smaller than end date.
}
else if dateComparisionResult == NSComparisonResult.OrderedDescending
{
    // Current date is greater than end date.
}
else if dateComparisionResult == NSComparisonResult.OrderedSame
{
    // Current date and end date are same.
}

TimeStamp

如果需要将某个TimeStamp("/Date(1427909016000-0800)”)转化为NSDate对象，那么可以使用如下的扩展工具，该扩展将会把TimeStamp转化为本地化时间。其中1427909016000表示从Unix计时以来的毫秒数，而-0800表示时区：

extension NSDate {
    convenience init?(jsonDate: String) {
        let prefix = "/Date("
        let suffix = ")/"
        let scanner = NSScanner(string: jsonDate)
        
        // Check prefix:
        if scanner.scanString(prefix,intoString: nil) {
            
            // Read milliseconds part:
            var milliseconds : Int64 = 0
            if scanner.scanLongLong(&milliseconds) {
                // Milliseconds to seconds:
                var timeStamp = NSTimeInterval(milliseconds)/1000.0
                
                // Read optional timezone part:
                var timeZoneOffset : Int = 0
                if scanner.scanInteger(&timeZoneOffset) {
                    let hours = timeZoneOffset / 100
                    let minutes = timeZoneOffset % 100
                    // Adjust timestamp according to timezone:
                    timeStamp += NSTimeInterval(3600 * hours + 60 * minutes)
                }
                
                // Check suffix:
                if scanner.scanString(suffix,intoString: nil) {
                    // Success! Create NSDate and return.
                    self.init(timeIntervalSince1970: timeStamp)
                    return
                }
            }
        }
        
        // Wrong format,return nil. (The compiler requires us to
        // do an initialization first.)
        self.init(timeIntervalSince1970: 0)
        return nil
    }
}

使用的例子如下：

if let theDate = NSDate(jsonDate: "/Date(1427909016000-0800)/")
{
    println(theDate)
}
else
{
    println("wrong format")
}

NSDateFormatter：格式化时间

var dataString = "April 1,2015" as String
var dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "MM-dd-yyyy"
dateFormatter.timeZone = NSTimeZone.localTimeZone()

// convert string into date
let dateValue = dateFormatter.dateFromString(dataString) as NSDate!

println(dateValue)

NSCalendar

// Playground - noun: a place where people can play

import UIKit

// Setup the calendar object
let calendar = NSCalendar.currentCalendar()

// Set up date object
let date = NSDate()

// Create an NSDate for the first and last day of the month
//let components = calendar.components(NSCalendarUnit.CalendarUnitYear |
//                                     NSCalendarUnit.CalendarUnitMonth |
//                                     NSCalendarUnit.WeekdayCalendarUnit |
//                                     NSCalendarUnit.WeekCalendarUnit |
//                                     NSCalendarUnit.CalendarUnitDay,//                                     fromDate: date)

// Create an NSDate for the first and last day of the month
let components = NSCalendar.currentCalendar().components(NSCalendarUnit.CalendarUnitMonth,fromDate: date)


components.month

// Getting the First and Last date of the month
components.day = 1
let firstDateOfMonth: NSDate = calendar.dateFromComponents(components)!

components.month  += 1
components.day     = 0
let lastDateOfMonth: NSDate = calendar.dateFromComponents(components)!

var unitFlags = NSCalendarUnit.WeekOfMonthCalendarUnit |
                NSCalendarUnit.WeekdayCalendarUnit     |
                NSCalendarUnit.CalendarUnitDay

let firstDateComponents = calendar.components(unitFlags,fromDate: firstDateOfMonth)
let lastDateComponents  = calendar.components(unitFlags,fromDate: lastDateOfMonth)

// Sun = 1,Sat = 7
let firstWeek = firstDateComponents.weekOfMonth
let lastWeek  = lastDateComponents.weekOfMonth

let numOfDatesToPrepend = firstDateComponents.weekday - 1
let numOfDatesToAppend  = 7 - lastDateComponents.weekday + (6 - lastDateComponents.weekOfMonth) * 7

let startDate: NSDate = calendar.dateByAddingUnit(NSCalendarUnit.CalendarUnitDay,value: -numOfDatesToPrepend,toDate: firstDateOfMonth,options: nil)!
let endDate:   NSDate = calendar.dateByAddingUnit(NSCalendarUnit.CalendarUnitDay,value: numOfDatesToAppend,toDate: lastDateOfMonth,options: nil)!

Array(map(0..<42) {
    calendar.dateByAddingUnit(NSCalendarUnit.CalendarUnitDay,value: $0,toDate: startDate,options: nil)!
})

"(components.year)"


var dateString = "2014-10-3" // change to your date format
var dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "YYYY-MM-dd"

var someDate = dateFormatter.dateFromString(dateString)
println(someDate)

（编辑：李大同）

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