Date to milliseconds and back to date in Swift

Question

I am taking the current time, in UTC, and putting it in nanaoseconds and then I need to take the nanoseconds and go back to a date in local time. I am able to do get the time to nanoseconds and then back to a date string but the time gets convoluted when I go from a string to date.

    //Date to milliseconds      func currentTimeInMiliseconds() -> Int! {             let currentDate = NSDate()             let dateFormatter = DateFormatter()             dateFormatter.dateFormat = format             dateFormatter.timeZone = NSTimeZone(name: "UTC") as TimeZone!             let date = dateFormatter.date(from: dateFormatter.string(from: currentDate as Date))             let nowDouble = date!.timeIntervalSince1970             return Int(nowDouble*1000)         }      //Milliseconds to date     extension Int {         func dateFromMilliseconds(format:String) -> Date {             let date : NSDate! = NSDate(timeIntervalSince1970:Double(self) / 1000.0)             let dateFormatter = DateFormatter()             dateFormatter.dateFormat = format             dateFormatter.timeZone = TimeZone.current             let timeStamp = dateFormatter.string(from: date as Date)  let formatter = DateFormatter()             formatter.dateFormat = format             return ( formatter.date( from: timeStamp ) )!         }     } 

//The timestamp is correct but the date returned isn't

Answer 1

I don't understand why you're doing anything with strings...

extension Date {     var millisecondsSince1970:Int64 {         Int64((self.timeIntervalSince1970 * 1000.0).rounded())     }          init(milliseconds:Int64) {         self = Date(timeIntervalSince1970: TimeInterval(milliseconds) / 1000)     } }   Date().millisecondsSince1970 // 1476889390939 Date(milliseconds: 0) // "Dec 31, 1969, 4:00 PM" (PDT variant of 1970 UTC) 

Answer 2

As @Travis Solution works but in some cases

var millisecondsSince1970:Int WILL CAUSE CRASH APPLICATION ,

with error

Double value cannot be converted to Int because the result would be greater than Int.max if it occurs Please update your answer with Int64

Here is Updated Answer

extension Date {  var millisecondsSince1970:Int64 {         return Int64((self.timeIntervalSince1970 * 1000.0).rounded())          //RESOLVED CRASH HERE     }      init(milliseconds:Int) {         self = Date(timeIntervalSince1970: TimeInterval(milliseconds / 1000))     } } 

---

About Int definitions.

On 32-bit platforms, Int is the same size as Int32, and on 64-bit platforms, Int is the same size as Int64.

Generally, I encounter this problem in iPhone 5, which runs in 32-bit env. New devices run 64-bit env now. Their Int will be Int64.

Hope it is helpful to someone who also has same problem