NSTimer does not count down in while loop - ios

Question

int maximumMinute;
NSTimer *timer;
- (void)startTimer: (int) minute {
maximumMinute = minute;
timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:#selector(countDown) userInfo:nil repeats:YES];
}
- (void)countDown {
maximumMinute -= 1;
self.timerLabel.text = [NSString stringWithFormat:#"%i", maximumMinute];
if (maximumMinute == 0) {
[timer invalidate];
}
}
This is my timer code and i just start the timer in viewDidLoad
i have this method called when some view is clicked for just testing.
-(void)clickSomthing: (UITapGestureRecognizer *)recognizer {
int i = 0;
while ([timer isValid])
{
NSLog(#"timer valid");
}
Firstly, when the view is loaded, the timer count is fired and i can see the time count down actually but when i click any view associated with the method "clickSomething" the timer does not count down actually it stops.
What i really want to do is that i want the timer keep going on until it reaches zero regardless of while or for loop. Actually, I am trying to stop my game based on the timer but the game does need some while loop and for loop that would take a while.

Answer 1

Your code lock the main thread (you never should do this) you should use GCD - Grand Central Dispatch to let the countdown in background while the user keep using the app.
-(void)clickSomthing: (UITapGestureRecognizer *)recognizer {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
int countDown = 10; // This is the countdown time
BOOL letTheCountDown = TRUE;
while (letTheCountDown) {
[NSThread sleepForTimeInterval:1.0]; // Count second by second
countDown--;
NSLog(#"countDown %i",countDown);
if (countDown == 0) {
letTheCountDown = FALSE;
dispatch_async(dispatch_get_main_queue(), ^{
// Do something in main thread here. Ex: alert
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Alert" message:#"Time is Over" delegate:self cancelButtonTitle:#"Okay" otherButtonTitles:nil];
[alert show];
});
}
}
});
}