问如何在应用程序的导航流中使用NSTimer？

EN

- (void)stopTimer
{
    if( timer )
    {
        [timer invalidate];
        [timer release]; // if not ARC
        timer = nil;
    }
}

- (void)startTimer
{
    [self stopTimer];
    int interval = 1.;
    timer = [[NSTimer scheduledTimerWithTimeInterval:interval
                                              target:self
                                            selector:@selector(countUp)
                                            userInfo:nil repeats:YES] retain]; // retain if not ARC
}

-(void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    [self timerStart];
}

-(void)viewWillDisappear:(BOOL)animated
{
    [self stopTimer];
    [super viewWillDisappear:animated];
}

-(void)countUp
{
    if(timePassed++ >= 60)  // defined in header
    {
        timePassed=0;
        [self myCustomEvent];
    }
}