Animate change of view controllers without using navigation controller stack, subviews or modal controllers?

EDIT: New answer that works in any orientation. The original answer only works when the interface is in portrait orientation. This is b/c view transition animations that replace a view w/ a different view must occur with views at least a level below the first view added to the window (e.g. window.rootViewController.view.anotherView).

I've implemented a simple container class I called TransitionController. You can find it at https://gist.github.com/1394947.

As an aside, I prefer the implementation in a separate class b/c it's easier to reuse. If you don't want that, you could simply implement the same logic directly in your app delegate eliminating the need for the TransitionController class. The logic you'd need would be the same however.

Use it as follows:

In your app delegate

// add a property for the TransitionController

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    MyViewController *vc = [[MyViewContoller alloc] init...];
    self.transitionController = [[TransitionController alloc] initWithViewController:vc];
    self.window.rootViewController = self.transitionController;
    [self.window makeKeyAndVisible];
    return YES;
}

To transition to a new view controller from any view controller

- (IBAction)flipToView
{
    anotherViewController *vc = [[AnotherViewController alloc] init...];
    MyAppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
    [appDelegate.transitionController transitionToViewController:vc withOptions:UIViewAnimationOptionTransitionFlipFromRight];
}

EDIT: Original Answer below - only works for portait orientation

I made the following assumptions for this example:

1. You have a view controller assigned as the rootViewController of your window

2. When you switch to a new view you want to replace the current viewController with the viewController owning the new view. At any time, only the current viewController is alive (e.g. alloc'ed).

The code can be easily modified to work differently, the key point is the animated transition and the single view controller. Make sure you don't retain a view controller anywhere outside of assigning it to window.rootViewController.

Code to animate transition in app delegate

- (void)transitionToViewController:(UIViewController *)viewController
                    withTransition:(UIViewAnimationOptions)transition
{
    [UIView transitionFromView:self.window.rootViewController.view
                        toView:viewController.view
                      duration:0.65f
                       options:transition
                    completion:^(BOOL finished){
                        self.window.rootViewController = viewController;
                    }];
}

Example use in a view controller

- (IBAction)flipToNextView
{
    AnotherViewController *anotherVC = [[AnotherVC alloc] init...];
    MyAppDelegate *appDelegate = (MyAppDelegate *)[UIApplication sharedApplication].delegate;
    [appDelegate transitionToViewController:anotherVC
                             withTransition:UIViewAnimationOptionTransitionFlipFromRight];
}

You can use Apple's new viewController containment system. For more in-depth information check out the WWDC 2011 session video "Implementing UIViewController Containment".

New to iOS5, UIViewController Containment allows you to have a parent viewController and a number of child viewControllers that are contained within it. This is how the UISplitViewController works. Doing this you can stack view controllers in a parent, but for your particular application you are just using the parent to manage the transition from one visible viewController to another. This is the Apple approved way of doing things and animating from one child viewController is painless. Plus you get to use all the various different UIViewAnimationOption transitions!

Also, with UIViewContainment, you do not have to worry, unless you want to, about the messiness of managing the child viewControllers during orientation events. You can simply use the following to make sure your parentViewController forwards rotation events to the child viewControllers.

- (BOOL)automaticallyForwardAppearanceAndRotationMethodsToChildViewControllers{
    return YES;
}

You can do the following or similar in your parent's viewDidLoad method to setup the first childViewController:

[self addChildViewController:self.currentViewController];
[self.view addSubview:self.currentViewController.view];
[self.currentViewController didMoveToParentViewController:self];
[self.currentViewController.swapViewControllerButton setTitle:@"Swap" forState:UIControlStateNormal];

then when you need to change the child viewController, you call something along the lines of the following within the parent viewController:

-(void)swapViewControllers:(childViewController *)addChildViewController:aNewViewController{
     [self addChildViewController:aNewViewController];
     __weak __block ViewController *weakSelf=self;
     [self transitionFromViewController:self.currentViewController
                       toViewController:aNewViewController
                               duration:1.0
                                options:UIViewAnimationOptionTransitionCurlUp
                             animations:nil
                             completion:^(BOOL finished) {
                                   [aNewViewController didMoveToParentViewController:weakSelf];

                                   [weakSelf.currentViewController willMoveToParentViewController:nil];
                                   [weakSelf.currentViewController removeFromParentViewController];

                                   weakSelf.currentViewController=[aNewViewController autorelease];
                             }];
 }

I posted a full example project here: https://github.com/toolmanGitHub/stackedViewControllers. This other project shows how to use UIViewController Containment on some various input viewController types that do not take up the whole screen. Good luck

OK, I know the question says without using a navigation controller, but no reason not to. OP wasn't responding to comments in time for me to go to sleep. Don't vote me down. :)

Here's how to pop the current view controller and flip to a new view controller using a navigation controller:

UINavigationController *myNavigationController = self.navigationController;
[[self retain] autorelease];

[myNavigationController popViewControllerAnimated:NO];

PreferencesViewController *controller = [[PreferencesViewController alloc] initWithNibName:nil bundle:nil];

[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration: 0.65];
[UIView setAnimationTransition:UIViewAnimationTransitionFlipFromRight forView:myNavigationController.view cache:YES];
[myNavigationController pushViewController:controller animated:NO];
[UIView commitAnimations];

[controller release];