Question

I have UIViewControllers A and B, they are allocated in AppDelegate. I need to apply transition to them. How to transit them without reallocating and replacing UIViews?
This code calls from my UIBarButtonItem in UINavigationController:

[UIView transitionFromView:self.view  //UIViewController A
                           toView:appDelegate.secondViewController.view //UIViewController B
                           duration:0.5 
                           options:UIViewAnimationOptionTransitionFlipFromLeft   

This method replaces UIViews in my UIViewControllers, and I can transit them back, or just don’t know how to do that. Can you tell me how to do this?

Answer 1

If you’re in iOS 5 world and want to jump between various view controllers, you might want to pursue View Controller Containment. Or check out WWDC 2011 session 102.

View controller containment basically assumes that you have some parent view controller which is governing the navigation between multiple child controllers. In your case, the parent view would be one with the navigation bar with the button on it.

Update:

If you pursue containment, you could create a parent view controller that has a nav bar with the button on it. When you load that view, you can add the first child view. Thus viewDidLoad might look like:

- (void)viewDidLoad
{
    [super viewDidLoad];

    // this is my model, where I store data used by my view controllers

    _model = [[MyModel alloc] init];

    // let's create our first view controller

    OneViewController *controller = [[OneViewController  alloc] initWithNibName:@"OneViewController"  bundle:nil];

    // pass it our model (obviously, `model` is a property that I've set up in my child controllers)

    controller.model = _model;

    // let's put the new child in our container and add it to the view

    [self addChildViewController:controller];
    [self configureChild:controller];
    [self.view addSubview:controller.view];
    [controller didMoveToParentViewController:self];

    // update our navigation bar title and the label of the button accordingly

    [self updateTitles:controller];
}

The configureChild just does final configuration. As a matter of convenience, I frequently will have a UIView that I’ve set up in IB (in this case, called childView) which I use for setting up the frame, which gets me out of the world of manually creating frames, but you can do it any way you want:

- (void)configureChild:(UIViewController *)controller
{
    // configure it to be the right size (I create a childView in IB that is convenient for setting the size of the views of our child view controllers)

    controller.view.frame = self.childView.frame;
}

This is the action if you touch the button in the navigation bar. If you’re in the first controller, set up the second controller. If you’re in the second controller, set up the first one:

- (IBAction)barButtonTouchUpInside:(id)sender 
{
    UIViewController *currentChildController = [self.childViewControllers objectAtIndex:0];

    if ([currentChildController isKindOfClass:[OneViewController class]])
    {
        TwoViewController *newChildController = [[TwoViewController alloc] initWithNibName:@"TwoViewController"  bundle:nil];
        newChildController.model = _model;
        [self transitionFrom:currentChildController To:newChildController];
    }
    else if ([currentChildController isKindOfClass:[TwoViewController class]])
    {
        OneViewController *newChildController = [[OneViewController alloc] initWithNibName:@"OneViewController"  bundle:nil];
        newChildController.model = _model;
        [self transitionFrom:currentChildController To:newChildController];
    }
    else
        NSAssert(FALSE, @"Unknown controller type");

}

This does the basic transition (including the various containment related calls):

- (void)transitionFrom:(UIViewController *)oldController To:(UIViewController *)newController
{    
    [self addChildViewController:newController];
    [self configureChild:newController];

    [self transitionFromViewController:oldController 
                      toViewController:newController
                              duration:0.5
                               options:UIViewAnimationOptionTransitionCrossDissolve
                            animations:^{
                                [self updateTitles:newController];
                            }
                            completion:^(BOOL finished){
                                [oldController willMoveToParentViewController:nil];
                                [oldController removeFromParentViewController];
                                [newController didMoveToParentViewController:self];
                            }];
}

This method just sets up the title in the nav bar in our parent view controller based upon which child is selected. It also sets up the button to reference the other controller.

- (void)updateTitles:(UIViewController *)controller
{
    if ([controller isKindOfClass:[OneViewController class]])
    {
        self.navigationItemTitle.title = @"First View Controller";  // current title
        self.barButton.title = @"Two";                              // title of button to take me to next controller
    }
    else if ([controller isKindOfClass:[TwoViewController class]])
    {
        self.navigationItemTitle.title = @"Second View Controller"; // current title
        self.barButton.title = @"One";                              // title of button to take me to next controller
    }
    else
        NSAssert(FALSE, @"Unknown controller type");
}

This all assumes you are going to create and destroy controllers as you jump between them. I generally do this, but use a model object to store my data so I keep whatever data I want.

You said you don’t want to do this “without reallocating and replacing UIViews”: If so, you can also change the above code to create both child view controllers up-front and change the transition to be simply jump between them:

- (void)viewDidLoad
{
    [super viewDidLoad];

    // this is my model, where I store data used by my view controllers

    _model = [[MyModel alloc] init];

    // let's create our first view controller

    _controller0 = [[OneViewController  alloc] initWithNibName:@"OneViewController"  bundle:nil];
    _controller0.model = _model;
    [self addChildViewController:_controller0];
    [self configureChild:_controller0];
    [_controller0 didMoveToParentViewController:self];

    // let's create our second view controller

    _controller1 = [[OneViewController  alloc] initWithNibName:@"OneViewController"  bundle:nil];
    _controller1.model = _model;
    [self addChildViewController:_controller1];
    [self configureChild:_controller1];
    [_controller1 didMoveToParentViewController:self];

    // let's add the first view and update our navigation bar title and the label of the button accordingly

    _currentChildController = _controller0;
    [self.view addSubview:_currentChildController.view];
    [self updateTitles:_currentChildController];
}

- (void)transitionFrom:(UIViewController *)oldController To:(UIViewController *)newController
{    
    [self transitionFromViewController:oldController 
                      toViewController:newController
                              duration:0.5
                               options:UIViewAnimationOptionTransitionCrossDissolve
                            animations:^{
                                [self updateTitles:newController];
                            }
                            completion:^(BOOL finished){
                                _currentChildController = newController;
                            }];
}

- (IBAction)barButtonTouchUpInside:(id)sender 
{
    UIViewController *newChildController;

    if ([_currentChildController isKindOfClass:[OneViewController class]])
    {
        newChildController = _controller1;
    }
    else if ([_currentChildController isKindOfClass:[TwoViewController class]])
    {
        newChildController = _controller0;
    }
    else
        NSAssert(FALSE, @"Unknown controller type");

    [self transitionFrom:_currentChildController To:newChildController];

}

I’ve seen it both ways, so you can do whatever works for you.