Date（）和Calendar.dateComponents的日期不匹配

Question

I'm trying to get the current date to print in a particular format (YYYYMMD) for AWS security credentials and I noticed that when I do Date() , the day is the 4th which is the correct value:

    let date = Date()
    print("\(date)")  //2016-10-04 00:56:28 +0000

Now, I want to print the date in the format I desire so, but I keep getting the day value as the 3rd:

    let calendar = Calendar.current
    let date = Date()
    let components = calendar.dateComponents([.day], from: date)
    print("\(components.day)")  //Optional(3)

S3 is expecting the date to be the 4th. How can I fix this?

Answer 1

It's because of time zone difference. date will return the UTC time and date but calendar will return the date and time based on your device's time zone. If you need the day number in UTC just set the time zone of the calendar object to UTC after you create it:

let calendar = Calendar.current
calendar.timeZone = TimeZone(abbreviation: "UTC")!

Now it will always match the value that is returned by Date()

Answer 2

When you print a date using

 print("\(date)")

You get the date and time in UTC, which is probably not what you want.

If you want to display your date in your local time zone, create a date formatter and use that:

let dateFormatter = NSdateFormatter()
let dateFormatter.dateStyle = .medium
let dateFormatter.timeStyle = .medium

let dateString = dateFormatter.StringFromDate(date)
print ("date = \(dateString)")

If you do this a lot, you might want to create an extension on NSDate displayString so you can use that to display your dates without having to write additional code.