Time Zone conversion troubles: a day off

[Trent McDougall]

Hi,

I know if you google about this there are a lot of results that come up but unfortunately nothing seems to be working for me.

I am trying to make a simple app that among other things converts from one time zone (gained from a UIDatePicker) to another but it in some instances it returns a date that is a day off.

I tried doing things this way:

 
viewDidLoad {
datePicker.timeZone = [NSTimeZone timeZoneWithName:@"America/Los_Angeles"];
[super viewDidLoad];
}
- (IBAction)datePickerValueDidChange:(id)sender {

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

[dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"Australia/Sydney"];   

NSLog(@"%@",[dateFormatter stringFromDate:datePicker.date]);
}

and this way:

 
- (IBAction)datePickerValueDidChange:(id)sender {
NSTimeZone* sourceTimeZone = datePicker.timeZone;
        
        NSTimeZone* destinationTimeZone = NSTimeZone timeZoneWithName:@"Australia/Sydney"];
        
        NSInteger sourceGMTOffset = [sourceTimeZone secondsFromGMTForDate:datePicker.date];
        NSInteger destinationGMTOffset = [destinationTimeZone secondsFromGMTForDate:datePicker.date];
        NSTimeInterval interval = destinationGMTOffset - sourceGMTOffset;
        
        NSDate* date = [[[NSDate alloc] initWithTimeInterval:interval sinceDate:datePicker.date] autorelease];

        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

[dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"Australia/Sydney"];  

        NSLog(@"%@",[dateFormatter stringFromDate:date]);

But regardless of which method I use, if I input 7:01 am 7/16/11 (LA time) into the date picker for example it returns the date 12:01 am 7/16/11 (sydney time) when it should actually read 12:01 am 7/17/11 (one day later).

Im not sure if Im just doing something sill or what but has anyone got any ideas where I'm going wrong?

[Duncan C]

Originally Posted by Trent McDougall

Hi,

I know if you google about this there are a lot of results that come up but unfortunately nothing seems to be working for me.

I am trying to make a simple app that among other things converts from one time zone (gained from a UIDatePicker) to another but it in some instances it returns a date that is a day off.

I tried doing things this way:

 
viewDidLoad {
datePicker.timeZone = [NSTimeZone timeZoneWithName:@"America/Los_Angeles"];
[super viewDidLoad];
}
- (IBAction)datePickerValueDidChange:(id)sender {

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

[dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"Australia/Sydney"];   

NSLog(@"%@",[dateFormatter stringFromDate:datePicker.date]);
}

and this way:

 
- (IBAction)datePickerValueDidChange:(id)sender {
NSTimeZone* sourceTimeZone = datePicker.timeZone;
        
        NSTimeZone* destinationTimeZone = NSTimeZone timeZoneWithName:@"Australia/Sydney"];
        
        NSInteger sourceGMTOffset = [sourceTimeZone secondsFromGMTForDate:datePicker.date];
        NSInteger destinationGMTOffset = [destinationTimeZone secondsFromGMTForDate:datePicker.date];
        NSTimeInterval interval = destinationGMTOffset - sourceGMTOffset;
        
        NSDate* date = [[[NSDate alloc] initWithTimeInterval:interval sinceDate:datePicker.date] autorelease];

        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

[dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"Australia/Sydney"];  

        NSLog(@"%@",[dateFormatter stringFromDate:date]);

But regardless of which method I use, if I input 7:01 am 7/16/11 (LA time) into the date picker for example it returns the date 12:01 am 7/16/11 (sydney time) when it should actually read 12:01 am 7/17/11 (one day later).

Im not sure if Im just doing something sill or what but has anyone got any ideas where I'm going wrong?

I'm not an expert on this stuff, but your code looks reasonable. I wonder if there's a bug in the system date conversion code?

P.S. I didn't realize there was such a huge time difference between LA and Sidney. Time differences of greater than 12 hours seem counter-intuitive.