iOS convert date to local time zone? - ios

Question

I know this is a very question and asked multiple times before.But this is something i get stuck every time.
Now, i want to convert a date string from web service which is in Argentina local zone(UTC-3:0) and want to convert this that to device local time zone(Suppose UTC+5:30). Here is my code
-(NSDate *)getLocaDateStringFromDate:(NSString *)sourceDate andSourceTime:(NSString *)sourceTime
{
//sourceDate is #"2015-10-16"; and sourceTime is #"00:00:00"
static NSDateFormatter* df = nil;
if (!df) {
df = [[NSDateFormatter alloc]init];
df.dateFormat = #"yyyy-MM-dd HH:mm:ss";
}
NSString* source = [sourceDate stringByAppendingString:[NSString stringWithFormat:#" %#", sourceTime]];
NSTimeZone *sourceZone = [NSTimeZone timeZoneWithAbbreviation:#"ART"];
[df setTimeZone: sourceZone];
NSDate *ds = [df dateFromString:source];
NSLog(#"sourceZone time is %#" , [df stringFromDate: ds]);//sourceZone time is 2015-10-16 00:00:00, correct!
NSTimeZone *localTimeZone = [NSTimeZone systemTimeZone];
[df setTimeZone: localTimeZone];
NSLog(#"local time is %#" , [df stringFromDate: ds]);//local time is 2015-10-16 08:30:00,, correct
NSString* str = [df stringFromDate: ds];
return [df dateFromString:str]; //this return 2015-10-16 03:00:00 +0000, why?
}
My question is that why my method return date in UTC, regardless of my time zone set to systemTimeZone. I get correct string but date is incorrect.
Any help would be appreciated.

Answer 1

1.) First, create an NSDateFormatter to get the NSDate sent from the server.
NSDateFormatter* dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"yyyy-MM-dd'T'HH:mm:ss'Z'"];
2.) Convert the date string to a NSDate.
NSDate* sourceDate = [dateFormatter dateFromString:dateString];
3) Specify ,Local and Destination timezone in which you want to convert your date.
For getting timezone of your source date:
NSTimeZone* sourceTimeZone = [NSTimeZone timeZoneWithAbbreviation:#"GMT"];
For getting User timezone :
NSTimeZone* destinationTimeZone = [NSTimeZone systemTimeZone];
4.) Calculate the inverval between source timezone and user timezone as given bellow:
NSInteger sourceGMTOffset = [sourceTimeZone secondsFromGMTForDate:sourceDate];
NSInteger destinationGMTOffset = [destinationTimeZone secondsFromGMTForDate:sourceDate];
NSTimeInterval interval = destinationGMTOffset - sourceGMTOffset;
NSDate* destinationDate = [[NSDate alloc] initWithTimeInterval:interval sinceDate:sourceDate];
5.) Now, create an NSDateFormatter for formatting date in which you want to show.
NSDateFormatter* dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setTimeZone:[NSTimeZone systemTimeZone]];
[dateFormat setDateFormat:#"M/d/yy 'at' h:mma"];
NSString* localTime = [dateFormat stringFromDate:destinationDate];
NSLog(#"localTime:%#", localTime);
Hope it is useful for you :)