iOS 計時器暫停和開始 防止重復點擊

-(IBAction)btnClick{
    [self starTimer];//開始計時
    //[self stopTimer];
}

-(NSTimer*)timer{
    if (!_timer) {
        _timer =[NSTimer scheduledTimerWithTimeInterval:5  target:self  selector:@selector(beginChange) userInfo:nil  repeats:YES];
    }
    return _timer;
}

//暫停定時器(只是暫停,並沒有銷毀timer)
-(void)pauseTimer{
    [self.timer setFireDate:[NSDate distantFuture]];
}
//繼續計時
-(void)continueTimer{
    [self.timer setFireDate:[NSDate distantPast]];
}

//開始計時
-(void)startimer{
    [self.timer fire];
}
//暫停並銷毀
-(void)stopTimer{
    [self.timer invalidate];
    self.timer = nil;
}

//開啟定時器
-(void)starTimer{
    [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(timerStar) object:nil];
    [self performSelector:@selector(timerStar) withObject:nil afterDelay:1];
}