Question

I’m trying to add a feature into my app that allows the user to toggle current date that is shown in US format (MM/DD/YYYY) to UK format (DD/MM/YYYY) and back.

I’m using a segment control to switch my UILabel (dateSlateLabel) between two separate timers (dateTimer_us & dateTimer_uk).

I’ve got everything working but whenever I toggle to the dateTimer_uk, dateTimer_us keeps fighting back, as if I haven’t killed it. When I say fighting back, I mean that I see the UK format with the US format blinking back and forth based on the timers’ timeInterval. So since my timers’ timeInterval is .01, I see a quick flashing of the US format over the UK format. Its clear to me that dateTimer_us is not being invalidated or something else is starting it back up. When I toggle to dateTimer_us, all seems fine, its just the other way around that is the problem, (when I toggle to dateTimer_uk). I figure something is wrong in my code/memory management but I can’t figure it out. I’ve scoured the web and spent two days on this problem.

Any ideas?

Note: I’ve tried using just one timer and an if else which checked the segmentControl status to drive the date format but that didn’t seem to work.

Here’s my code:

//////////////////////////////THIS CONTROLS THE DATE TIMER//////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////
- (IBAction)toggleDateFormat {

    if(dateFormatSegmentControl.selectedSegmentIndex == 0) {


        [dateTimer_uk invalidate];
        [dateTimer_uk release];
        dateTimer_uk = nil;

        [self dateTimer_us];


    }
    else if (dateFormatSegmentControl.selectedSegmentIndex == 1) {


        [dateTimer_us invalidate];
        [dateTimer_us release];
        dateTimer_us = nil;

        [self dateTimer_uk];


    }

}







-(void)dateTimer_us {

    dateTimer_us = [[NSTimer scheduledTimerWithTimeInterval: .01
                                                     target: self
                                                   selector: @selector(displayDate_us)
                                                   userInfo: nil
                                                    repeats: YES] retain];

}
-(void)displayDate_us; {

    NSDateFormatter *formatter =
    [[[NSDateFormatter alloc] init] autorelease];
    NSDate *date = [NSDate date];


    [formatter setDateFormat:@"MM/dd/yyyy"];
    [dateSlateLabel setText:[formatter stringFromDate:date]];



}
-(void)dateTimer_uk {


    dateTimer_uk = [[NSTimer scheduledTimerWithTimeInterval: .01
                                                     target: self
                                                   selector: @selector(displayDate_uk)
                                                   userInfo: nil
                                                    repeats: YES] retain];
}           
-(void)displayDate_uk; {

    NSDateFormatter *formatter =
    [[[NSDateFormatter alloc] init] autorelease];
    NSDate *date = [NSDate date];


    [formatter setDateFormat:@"dd/MM/yyyy"];
    [dateSlateLabel setText:[formatter stringFromDate:date]];   

}

Answer 1

The design you’ve shown here is needlessly complicated. For one, you’re asking for an interval of one hundredth of a second to update a label which represents the current time. This is roughly one hundred times too often to be firing.

Your design should be something like this:

• Add an NSDateFormatter property to your view controller class. You don’t need to expose
  this property publicly.
• In viewDidLoad,
  • alloc/init your NSDateFormatter property to whatever default setting you want, US or UK (you might read/write this preference from NSUserDefaults.
  • Start a timer on an interval of 1 second to call a method to update the label. This method should use the NSDateFormatter property, whatever value it is (the method doesn’t care) to render the date/time
• In your callback method to toggle the time format,
  • release the NSDateFormatter property and alloc/init a new one
• In viewDidUnload,
  • invalidate/release the NSTimer object