stopping a programming loop

When my main viewController is first clicked, it starts showing a demo (on repeat) as follows:

showingDemo = YES;
[self startDemo];

- (void)startDemo {
    if (showingDemo) {
        [self performSelector:@selector(stepone) withObject:nil afterDelay:1.5f];
        [self performSelector:@selector(steptwo) withObject:nil afterDelay:2.0f];
        [self performSelector:@selector(stepthree) withObject:nil afterDelay:3.8f];
        [self performSelector:@selector(stepfour) withObject:nil afterDelay:4.3f];  
        [self performSelector:@selector(startDemo) withObject:nil afterDelay:5.6f];
    }
}

When it is clicked a second time, I bring a new ViewController to the screen

showingDemo = NO;
[self.view addSubview:newView];

I thought this would stop the endless loop.

When the user returns back to my main viewController:

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[newView.view removeFromSuperview];

And clicks on the screen again:

showingDemo = YES;
[self startDemo];

In testing my app, if I click back quickly (before the loop has had time to end, the program seems to be running through the loop twice - the one that was previously going and the new one - and therefore it looks all weird, with the 'stepthree' function happening before 'stepone' and so forth.

Anybody know a better way to STOP the loop I've programmed for good so that when I go to start it again later, it doesn't run multiple loops thinking that the previous one hasn't been finished?

Thanks so much!

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When you set showingDemo to NO, call NSObject's cancelPreviousPerformRequestsWithTarget: to cancel any pending perform requests:

showingDemo = NO;
[NSObject cancelPreviousPerformRequestsWithTarget:self];
[self.view addSubview:newView];