如何暫停和恢復我的NSTimer

Question

我有一個已經可以工作的NSTimer，但是當您單擊按鈕時想暫停它。 除了暫停，此按鈕會將我重定向到其他視圖，然后當我返回到主視圖時，他必須從您上次停下的地方繼續。 我已經有了暫停按鈕，並且打算繼續計算在viewWillAppear上調用方法

這是我的代碼：

- (void)viewDidLoad {
    [super viewDidLoad];
    [self setUp];
}

- (void) setUp {
    _startDate = [NSDate date];
    _timer = [NSTimer scheduledTimerWithTimeInterval: 1.0/100.0 target: self selector: @selector(timerUpdating) userInfo: nil repeats: true];
}

-(void)timerUpdating {

    NSDate *currentDate = [NSDate date];
    NSTimeInterval timeInterval = [currentDate timeIntervalSinceDate:_startDate];
    NSDate *timerDate  = [NSDate dateWithTimeIntervalSince1970:timeInterval];
    NSDateFormatter *dateFormater = [[NSDateFormatter alloc]init];
    [dateFormater setDateFormat:@"mm:ss"];
    [dateFormater setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]];
    NSString *timeString = [dateFormater stringFromDate:timerDate];
    self.timerLabel.text = timeString;
    self.pauseTimeInterval = &(timeInterval);
}

- (IBAction)timerActionPause:(id)sender {
}

Answer 1

- (void)startTimer {
    if(_timer != nil) { // To make sure 
        [self stopTimer];
    }
    _timer = [NSTimer scheduledTimerWithTimeInterval: 1.0/100.0 target: self selector: @selector(timerUpdating) userInfo: nil repeats: true];
}

- (void)stopTimer {
    [_timer invalidate];
    _timer = nil;
}

- (void)resetTimer {
    [self stopTimer];
    [self startTimer];
}