Getting the current time and keeping it updated - Objective C - iphone

Question

I know how to use NSDate to get the time and display it inside UILabel.
i need to display the date + hours and minutes.
any idea how can i keep it updated without busy-waiting?
Thanks!

Answer 1

Use NSTimer to update time on the label
- (void)viewDidLoad
{
[super viewDidLoad];
[NSTimer scheduledTimerWithTimeInterval:1 target:self selector:#selector(updateTime) userInfo:nil repeats:YES];
}
-(void)updateTime
{
NSDate *date= [NSDate date];
NSDateFormatter *formatter1 = [[NSDateFormatter alloc]init]; //for hour and minute
formatter1.dateFormat = #"hh:mm a";// use any format
clockLabel.text = [formatter1 stringFromDate:date];
[formatter1 release];
}

Answer 2

As your comments said , if you want when minutes changes you change the label.text
you should do like this :
1st: get the current time:
NSDate *date = [NSDate date];
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *dateComponents = [calendar components:NSHourCalendarUnit fromDate:date];
and set the label.text = CURRENTHOUR_AND_YOURMINNUTS;
and then refresh the label next minute,like this :
the first , you can check after 60 - nowSeconds
[self performSelector:#selector(refreshLabel) withObject:nil afterDelay:(60 - dateComponents.minute)];
- (void)refreshLabel
{
//refresh the label.text on the main thread
dispatch_async(dispatch_get_main_queue(),^{ label.text = CURRENT_HOUR_AND_MINUTES; });
// check every 60s
[self performSelector:#selector(refreshLabel) withObject:nil afterDelay:60];
}
It will check every minute , so the effecent is more than answers above.
When refreshLabel invocated , it means the minutes changed

Answer 3

You can use the NSTimer to periodically get the current time.
[NSTimer scheduledTimerWithTimeInterval:2 target:self selector:#selector(timerFired:) userInfo:nil repeats:YES];
- (void)timerFired:(NSTimer*)theTimer{
//you can update the UILabel here.
}

Answer 4

You can use NSTimer , but , given the above methods , the UILabel won't update on touch Events as the main thread will be busy tracking it.You need to add it to mainRunLOOP
NSTimer* timer = [NSTimer timerWithTimeInterval:1.0f target:self selector:#selector(updateLabelWithDate) userInfo:nil repeats:YES];
[[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
-(void)updateLabelWithDate
{
//Update your Label
}
You can change the time interval(rate at which you want Updation).