Get UTC time and local time from NSDate object

Question

In objective-c, the following code results in the UTC date time information using the date API.

NSDate *currentUTCDate = [NSDate date] 

In Swift however,

let date = NSDate.date() 

results in local date and time.

I have two questions:

1. How can I get UTC time and local time (well date gives local time) in NSDate objects.
2. How can I get precision for seconds from the NSDate object.

EDIT 1: Thanks for all the inputs but I am not looking for NSDateFormatter objects or string values. I am simply looking for NSDate objects (however we cook them up but that's the requirement).
See point 1.

Answer 1

NSDate is a specific point in time without a time zone. Think of it as the number of seconds that have passed since a reference date. How many seconds have passed in one time zone vs. another since a particular reference date? The answer is the same.

Depending on how you output that date (including looking at the debugger), you may get an answer in a different time zone.

If they ran at the same moment, the values of these are the same. They're both the number of seconds since the reference date, which may be formatted on output to UTC or local time. Within the date variable, they're both UTC.

Objective-C:

NSDate *UTCDate = [NSDate date] 

Swift:

let UTCDate = NSDate.date() 

To explain this, we can use a NSDateFormatter in a playground:

import UIKit  let date = NSDate.date()     // "Jul 23, 2014, 11:01 AM" <-- looks local without seconds. But:  var formatter = NSDateFormatter() formatter.dateFormat = "yyyy-MM-dd HH:mm:ss ZZZ" let defaultTimeZoneStr = formatter.stringFromDate(date)     // "2014-07-23 11:01:35 -0700" <-- same date, local, but with seconds formatter.timeZone = NSTimeZone(abbreviation: "UTC") let utcTimeZoneStr = formatter.stringFromDate(date)     // "2014-07-23 18:01:41 +0000" <-- same date, now in UTC 

The date output varies, but the date is constant. This is exactly what you're saying. There's no such thing as a local NSDate.

As for how to get microseconds out, you can use this (put it at the bottom of the same playground):

let seconds = date.timeIntervalSince1970 let microseconds = Int(seconds * 1000) % 1000 // chops off seconds 

To compare two dates, you can use date.compare(otherDate).

Answer 2

Xcode 9 • Swift 4 (also works Swift 3.x)

extension Formatter {     // create static date formatters for your date representations     static let preciseLocalTime: DateFormatter = {         let formatter = DateFormatter()         formatter.locale = Locale(identifier: "en_US_POSIX")         formatter.dateFormat = "HH:mm:ss.SSS"         return formatter     }()     static let preciseGMTTime: DateFormatter = {         let formatter = DateFormatter()         formatter.locale = Locale(identifier: "en_US_POSIX")         formatter.timeZone = TimeZone(secondsFromGMT: 0)         formatter.dateFormat = "HH:mm:ss.SSS"         return formatter     }() } 

---

extension Date {     // you can create a read-only computed property to return just the nanoseconds from your date time     var nanosecond: Int { return Calendar.current.component(.nanosecond,  from: self)   }     // the same for your local time     var preciseLocalTime: String {         return Formatter.preciseLocalTime.string(for: self) ?? ""     }     // or GMT time     var preciseGMTTime: String {         return Formatter.preciseGMTTime.string(for: self) ?? ""     } } 

---

Playground testing

Date().preciseLocalTime // "09:13:17.385"  GMT-3 Date().preciseGMTTime   // "12:13:17.386"  GMT Date().nanosecond       // 386268973 

This might help you also formatting your dates: