How to get Current EST time IOS Swift

问题

I need to compare two dates in my app and i have a EST date to compare with current date , but let today = NSDate() returns the date in UTC , how can i get current EST time or convert to EST ?

回答1:

The NSDate store the time in absolute moment i.e. No matter in what time zone your date was created when you use compare method of NSDate it will respect the time zone (because time zone was never stored). You can think of NSDate as epoch time which is always calculated from 00:00:00 Coordinated Universal Time (UTC), Thursday, 1 January 1970

I don't know about the implementation of NSDate may be it store the date in UTC internally.

It's our implementation (NSDateFormatter) that changes it's format to our requirement.

So whether you use compare or NSCalendar regardless how you created your date they will compare you date

e.g. My local time zone is IST and it's 2016-10-21 12:10:00 here right now

In EST it's 2016-10-21 02:40:00,
In PST it's 2016-10-20 23:40:00 right now

So this code

let today = NSDate()
print("\(today)")


let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
formatter.timeZone = TimeZone(abbreviation: "EST")
let estDate = formatter.date(from: "2016-10-21 02:40:00")
print("\(estDate!)")


formatter.timeZone = TimeZone(abbreviation: "PST")
let pstDate = formatter.date(from: "2016-10-20 23:40:00")
print("\(pstDate!)")


formatter.timeZone = TimeZone(abbreviation: "IST")
let istDate = formatter.date(from: "2016-10-21 12:10:00")
print("\(istDate!)")

Will print the same time because it's the same moment everywhere

2016-10-21 06:40:00 +0000
2016-10-21 06:40:00 +0000
2016-10-21 06:40:00 +0000
2016-10-21 06:40:00 +0000

回答2:

Try This-

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

If you need to compare two dates, you can use the method below

// 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.
}

If you want to know all time zones abbreviations available you can do like this:

var timeZoneAbbreviationsType: [String:String] { return TimeZone.abbreviationDictionary }
timeZoneAbbreviationsType   // ["CEST": "Europe/Paris", "WEST": "Europe/Lisbon", "CDT": "America/Chicago", "EET": "Europe/Istanbul", "BRST": "America/Sao_Paulo", "EEST": "Europe/Istanbul", "CET": "Europe/Paris", "MSD": "Europe/Moscow", "MST": "America/Denver", "KST": "Asia/Seoul", "PET": "America/Lima", "NZDT": "Pacific/Auckland", "CLT": "America/Santiago", "HST": "Pacific/Honolulu", "MDT": "America/Denver", "NZST": "Pacific/Auckland", "COT": "America/Bogota", "CST": "America/Chicago", "SGT": "Asia/Singapore", "CAT": "Africa/Harare", "BRT": "America/Sao_Paulo", "WET": "Europe/Lisbon", "IST": "Asia/Calcutta", "HKT": "Asia/Hong_Kong", "GST": "Asia/Dubai", "EDT": "America/New_York", "WIT": "Asia/Jakarta", "UTC": "UTC", "JST": "Asia/Tokyo", "IRST": "Asia/Tehran", "PHT": "Asia/Manila", "AKDT": "America/Juneau", "BST": "Europe/London", "PST": "America/Los_Angeles", "ART": "America/Argentina/Buenos_Aires", "PDT": "America/Los_Angeles", "WAT": "Africa/Lagos", "EST": "America/New_York", "BDT": "Asia/Dhaka", "CLST": "America/Santiago", "AKST": "America/Juneau", "ADT": "America/Halifax", "AST": "America/Halifax", "PKT": "Asia/Karachi", "GMT": "GMT", "ICT": "Asia/Bangkok", "MSK": "Europe/Moscow", "EAT": "Africa/Addis_Ababa"]

来源：https://stackoverflow.com/questions/40169205/how-to-get-current-est-time-ios-swift