NSTimer Stopwatch - xcode

Question

I have a stopwatch that runs fine on my app however when I click on the back button to go to another view it stops. I want the stopwatch to keep running even when the user is viewing another page.
How do I accomplish this?
Ok added the code
code:
.h
UILabel *stopWatchLabel;
NSTimer *stopWatchTimer; // Store the timer that fires after a certain time
NSDate *startDate; // Stores the date of the click on the start button
#property (nonatomic, retain) IBOutlet UILabel *stopWatchLabel;
- (IBAction)onStartPressed:(id)sender;
- (IBAction)onStopPressed:(id)sender;
.m
- (void)viewDidUnload
{
[self setStopWatchLabel:nil];
[super viewDidUnload];
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}
- (void)updateTimer
{
NSDate *currentDate = [NSDate date];
NSTimeInterval timeInterval = [currentDate timeIntervalSinceDate:startDate];
NSDate *timerDate = [NSDate dateWithTimeIntervalSince1970:timeInterval];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"HH:mm:ss.SSS"];
[dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]];
NSString *timeString=[dateFormatter stringFromDate:timerDate];
stopWatchLabel.text = timeString;
}
- (IBAction)onStartPressed:(id)sender {
startDate = [NSDate date];
// Create the stop watch timer that fires every 10 ms
stopWatchTimer = [NSTimer scheduledTimerWithTimeInterval:1.0/10.0
target:self
selector:#selector(updateTimer)
userInfo:nil
repeats:YES];
}
- (IBAction)onStopPressed:(id)sender {
[stopWatchTimer invalidate];
stopWatchTimer = nil;
[self updateTimer];
}

Answer 1

Well it stops because you're releasing the view that it lives in when you pop it off the stack.
have you tried making a stopwatch class that handles the timer independent of the view?

Answer 2

The stopwatch stops because you're releasing the view that controls it.
You need to make sure that the NSTimer is not linked to any view.
Perhaps you can use subviews or Modal View Controllers (I think that may work) in order to not have the stopwatch released when the view is.
You could also try sending the stopwatch information to the next view through variables, and then having the other view take over the stopwatch from there.
There are most definitely other methods as well.
Either way, you need to make sure that the NSTimer is not released.

Answer 3

Exactly, if you look at your "ViewDidUnload" you're setting it to nil when the view gets released which it does when you go to another view.
Something you can try is to have a class that's running the timer and sending it over to the view that way it's still running even though the view that displays it is not in memory.
MVC style!

Answer 4

Yeah, what everyone else says.
On the ViewDidUnload it is releasing it. Meaning it is basically ending the operation as soon as that ViewController is exited.

Answer 5

I Dont know if the problem is already solved or not but still.
Create the Object of NSTimer in App Delegate Class and then instantiate the timer of in .m file of app delegate in this way your NSTimer will stay in memory. and when you want to stop or pause the timer you can just invalidate that object from any view Controller.