Question

in my application,I have implemented NSTimer to count time.I have swipe detection and when
the user swipes on the screen,animation runs continuously.my question is when I swipe
on the screen(left/right continuously) NSTimer slows down.
can anybody tell me how to solve this problem?

//code

    gameTimer = [NSTimer scheduledTimerWithTimeInterval:1.0/100
                                                          target:self
                                                        selector:@selector(updateGameTimer)
                                                        userInfo:nil
                                                        repeats:YES];

    -(void)updateGameTimer
    {
        counter++;
        tick++;
        if(tick==100){
            tick = 0;
            seconds += 1;
        }
        if(counter==100){
            counter = 0;
        }
        timerLabel.text = [NSString stringWithFormat:@"%i.%02d",seconds,counter];
    } 


//swipe detection

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
    [super touchesMoved:touches withEvent:event];

    UITouch *touch = [touches anyObject];
    //CGPoint curPt = [touch locationInView:self.view];    
    CGPoint newLocation = [touch locationInView:self.view];
    CGPoint oldLocation = [touch previousLocationInView:self.view];
    gameView.multipleTouchEnabled = true;

    if(newLocation.x-oldLocation.x>0){
        swipe_direction = 1;
        //NSLog(@"left");
    }
    else{
        swipe_direction = 2;
        //NSLog(@"right");

    }

    if(swipe_direction==1){
        //animate images
        //play sound effect
    }
    else if(swipe_direction==2){
       //animate images
       //play sound effect
    }

}

Answer 1

From the NSTimer documentation…

A timer is not a real-time mechanism; it fires only when one of the
run loop modes to which the timer has been added is running and able
to check if the timer’s firing time has passed. Because of the various
input sources a typical run loop manages, the effective resolution of
the time interval for a timer is limited to on the order of 50-100
milliseconds. If a timer’s firing time occurs during a long callout or
while the run loop is in a mode that is not monitoring the timer, the
timer does not fire until the next time the run loop checks the timer.
Therefore, the actual time at which the timer fires potentially can be
a significant period of time after the scheduled firing time.

Your timer resolution is 10 milliseconds, so if the run loop doesn’t not complete quickly enough (under 10 milliseconds), you’ll start to notice a lag between real-time, and your counters.

If you are implementing a game, devs will generally try to disassociate from the CPU or clock speed.

Take a look at this answer

or take a look at how a framework like cocos2d implements its own scheduler.