NSTimer : Update Label after switch View doesn't work - ios

Question

I want to use NSTimer as a Countdown. The counter works fine;-)!
But I I switch to another viewController the timer doesn't runs in "foreground" - so the label isn't updated.... after coming back to this view.
My NSLOG shows that the timer is still runnig, like I want ;-)
So in whicht way I have to work, that my timer update my label?
Here is the code:
- (IBAction)startClock:(id)sender {
globalTimer = 20;
timer = [NSTimer scheduledTimerWithTimeInterval:1.0
target:self
selector:#selector(updateCircularProgressBar)
userInfo:nil
repeats:YES];
}
- (void)updateCircularProgressBar
{
// Values to be passed on to Circular Progress Bar
if (globalTimer > 0 && globalTimer <= 1200) {
globalTimer--;
minutesLeft = globalTimer / 60;
secondsLeft = globalTimer % 60;
[self drawCircularProgressBarWithMinutesLeft:minutesLeft secondsLeft:secondsLeft];
NSLog(#"Time left: %02d:%02d", minutesLeft, secondsLeft);
}
else {
[self drawCircularProgressBarWithMinutesLeft:0 secondsLeft:0];
[timer invalidate];
}
}
I tested to run the "updateCircularProgressBar" in my viewDidLoad but this shows NO result...
THX for Help
UPDATE more with more Code:
/*-------------------- TIMER --------------------*/
// Draws the progress circles on top of the already painted background
- (void)drawCircularProgressBarWithMinutesLeft:(NSInteger)minutes secondsLeft:(NSInteger)seconds
{
// Removing unused view to prevent them from stacking up
for (id subView in [self.view subviews]) {
if ([subView isKindOfClass:[CircularProgressTimer class]]) {
[subView removeFromSuperview];
}
}
// Init our view and set current circular progress bar value
CGRect progressBarFrame = CGRectMake(0, 0, 180, 180);
progressTimerView = [[CircularProgressTimer alloc] initWithFrame:progressBarFrame];
[progressTimerView setCenter:CGPointMake(160, 210)];
[progressTimerView setPercent:seconds];
if (minutes == 0 && seconds <= 0) {
[progressTimerView setInstanceColor:[UIColor magentaColor]];
}
// Here, setting the minutes left before adding it to the parent view
[progressTimerView setMinutesLeft:minutesLeft];
[progressTimerView setSecondsLeft:secondsLeft];
[self.view addSubview:progressTimerView];
progressTimerView = nil;
}
The label is in another file (CircularProgressTimer) which controls the progessbar...