Truncating time off a date retains some time component [duplicate] - swift

Question

When I try to log the current date:
print(NSDate())
or
print(Date())
(in Swift 3)
Or any date object, it shows the wrong time. For example, it's about 16:12 now, but the above displayed
2016-10-08 20:11:40 +0000
Is my date in the wrong time zone? How do I fix my date to have the correct time zone?
Why is that, and how to I fix it? How do I easily display an arbitrary date in my local time zone, either in print statements or in the debugger?
(Note that this question is a "ringer" so that I can provide a simple Swift 3/Swift 2 Date/NSDate extension that lets you easily display any date object in your local time zone.

Answer 1

NSDate (or Date in Swift ≥ V3) does not have a time zone. It records an instant in time all over the world.
Internally, date objects record the number of seconds since the "epoch date", or Midnight on January 1, 2001 in Greenwich Mean Time, a.k.a UTC.
We normally think of dates in our local time zone.
If you log a date using
print(NSDate())
The system displays the current date, but it expresses it in UTC/Greenwich Mean Time. So the only place the time will look correct is in that time zone.
You get the same issue in the debugger if you issue the debugger command
e NSDate()
This is a pain. I personally wish iOS/Mac OS would display dates using the user's current time zone, but they don't.
EDIT #2:
An improvement on my previous use of localized string that makes it a little easier to use is to create an extension to the Date class:
extension Date {
func localString(dateStyle: DateFormatter.Style = .medium, timeStyle: DateFormatter.Style = .medium) -> String {
return DateFormatter.localizedString(from: self, dateStyle: dateStyle, timeStyle: timeStyle)
}
}
That way you can just use an expression like Date().localString(), or if you want to only print the time, you can use Date().localString(dateStyle:.none)
EDIT:
I just discovered that NSDateFormatter (DateFormatter in Swift 3) has a class method localizedString. That does what my extension below does, but more simply and cleanly. Here is the declaration:
class func localizedString(from date: Date, dateStyle dstyle: DateFormatter.Style, timeStyle tstyle: DateFormatter.Style) -> String
So you'd simply use
let now = Date()
print (DateFormatter.localizedString(
from: now,
dateStyle: .short,
timeStyle: .short))
You can pretty much ignore everything below.
I have created a category of the NSDate class (Date in swift 3) that has a method localDateString that displays a date in the user's local time zone.
Here is the category in Swift 3 form: (filename Date_displayString.swift)
extension Date {
#nonobjc static var localFormatter: DateFormatter = {
let dateStringFormatter = DateFormatter()
dateStringFormatter.dateStyle = .medium
dateStringFormatter.timeStyle = .medium
return dateStringFormatter
}()
func localDateString() -> String
{
return Date.localFormatter.string(from: self)
}
}
And in Swift 2 form:
extension NSDate {
#nonobjc static var localFormatter: NSDateFormatter = {
let dateStringFormatter = NSDateFormatter()
dateStringFormatter.dateStyle = .MediumStyle
dateStringFormatter.timeStyle = .MediumStyle
return dateStringFormatter
}()
public func localDateString() -> String
{
return NSDate.localFormatter.stringFromDate(self)
}
}
(If you prefer a different date format it's pretty easy to modify the format used by the date formatters. It's also straightforward to display the date and time in any timezone you need.)
I would suggest putting the appropriate Swift 2/Swift 3 version of this file in all of your projects.
You can then use
Swift 2:
print(NSDate().localDateString())
Swift 3:
print(Date().localDateString())

Answer 2

A simple way to correct the Date for your timezone would be to use TimeZone.current.secondsFromGMT()
Something like this for a local timestamp value for example:
let currentLocalTimestamp = (Int(Date().timeIntervalSince1970) + TimeZone.current.secondsFromGMT())