Convert date from timezone to device local timezone and date - ios

Question

How can I convert date with timezone1 to date with device local timezone2?
NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:#"YYYY-MM-dd HH:mm:ss"];
[dateFormat setTimeZone:[NSTimeZone timeZoneWithName:#"Asia/Jerusalem"]];
NSDate *date = [dateFormat dateFromString:timestamp];
then something like:
[dateFormat2 setTimeZone:[NSTimeZone localTimeZone]];
date2 = [dateFormat2 dateFromDate:date withOtherTimeZone:zone];
UPDATE:
I think I got it.
//get source date from the server
NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:#"YYYY-MM-dd HH:mm:ss"];
NSDate *sourceDate = [dateFormat dateFromString:timestamp];
//set timezones
NSTimeZone* sourceTimeZone = [NSTimeZone timeZoneWithName:#"Asia/Jerusalem"];
NSTimeZone* destinationTimeZone = [NSTimeZone systemTimeZone];
//calc time difference
NSInteger sourceGMTOffset = [sourceTimeZone secondsFromGMTForDate:sourceDate];
NSInteger destinationGMTOffset = [destinationTimeZone secondsFromGMTForDate:sourceDate];
NSTimeInterval interval = destinationGMTOffset - sourceGMTOffset;
//set current real date
NSDate* date = [[NSDate alloc] initWithTimeInterval:interval sinceDate:sourceDate];
Is it ok?

Answer 1

OK first off, time is time. At this very second, everywhere on earth, its is the same second. Stop thinking of time format as time. It's not. All time should be in GMT, and then you can display it based on TimeZone.
Date *d = [NSDate date] ;
NSDateFormatter *df = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:#"YYYY-MM-dd HH:mm:ss Z"];
NSTimeZone *nyTimeZone = [NSTimeZone timeZoneWithAbbreviation:#"sometimeabbr."];
NSTimeZone *localTimeZone = [NSTimeZone systemTimeZone];
[df setTimezone: nyTimeZone];
NSLog(#"ny time is %#" , [df stringFromDate: d]);
[df setTimeZone: localTimeZone];
NSLog(#"local time is %#" , [df stringFromDate: d]);
If you are given a string date and need to convert, create NSDateFormatter to ingest the string date. Make sure you set a timezone. Now you have a NSDate object (no timezone in NSDates), that yiou can format into any other timezone you want.
Please for the love all all that is holy. Treat time as seconds that marches forward, and timezones as the formatting of those timezones.

Answer 2

This is the answer:
NSTimeZone* sourceTimeZone = [NSTimeZone timeZoneWithName:#"Asia/Jerusalem"];
NSTimeZone* destinationTimeZone = [NSTimeZone systemTimeZone];
//calc time difference
NSInteger sourceGMTOffset = [sourceTimeZone secondsFromGMTForDate:sourceDate];
NSInteger destinationGMTOffset = [destinationTimeZone secondsFromGMTForDate:sourceDate];
NSTimeInterval interval = destinationGMTOffset - sourceGMTOffset;
//set current real date
NSDate* date = [[NSDate alloc] initWithTimeInterval:interval sinceDate:sourceDate];

Answer 3

*Different time zone date convert to local time zone date in swift.
let timeZone1 = NSTimeZone(name: timeZone1Name)
let localTimeZone = NSTimeZone.localTimeZone()
let timeZone1Interval = timeZone1?.secondsFromGMTForDate(timezone1Date!)
let deviceTimeZoneInterval = localTimeZone.secondsFromGMTForDate(timezone1Date!)
let timeInterval = Double(timeZone1Interval! - deviceTimeZoneInterval)
let originalDate = NSDate(timeInterval: timeInterval, sinceDate: timezone1Date!)
let dateFormater : NSDateFormatter = NSDateFormatter()
dateFormater.dateFormat = "YYYY-MM-dd HH:mm:ss Z"
NSLog("Converted date: \(dateFormater.stringFromDate(originalDate))")
let dateString = dateFormater.stringFromDate(originalDate)
let localTimeZoneDate = dateFormater.dateFromString(dateString)
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