Switching between view controllers

[erfmufn]

Is it necessary to use a third dedicated UIViewcontroller for navigation between 2 view controllers, or can an app be programmed to call another viewcontroller into view when, say, a UIButton is pushed?

Apologies in advance for simple question.

[erfmufn]

Well through some trial and error I've worked out I don't need a third controller and I can call a switch method in the delegate which is pretty neat. Now my only problem is that it ignores the landscape orientation I've set.

- (void)switchView 
{
    if (instructionsViewController == nil)
    { 
        [viewController.view removeFromSuperview];
        [viewController release];
        viewController = nil;
		
        instructionsViewController = [[InstructionsViewController alloc]init];
        [window addSubview:instructionsViewController.view];
    }
    else
    {
        [instructionsViewController.view removeFromSuperview];
		[instructionsViewController release];
		instructionsViewController = nil;
		
		viewController = [[PianoTutorViewController alloc]init];
        [window addSubview:viewController.view];
    }
}

Not sure if code is elegant, but works apart from the landscape issue.