View Controllers: How to switch between views programmatically?

Question

In short: I want to have two fullscreen views, where I can switch between view A and view B. I know I could just use an Tab Bar Controller, but I dont want to. I want to see how this is done by hand, for learning what's going on under the hood.

I have an UIViewController that acts as an root controller:

@interface MyRootController : UIViewController {     IBOutlet UIView *contentView; } @property(nonatomic, retain) UIView *contentView;  @end 

The contentView is hooked up to an UIView which I added as an subview to the "view" of the Nib. This has green color and I see it fullscreen. Works fine.

Then, I created two other View Controllers pretty much the same way. ViewControllerA and ViewControllerB. ViewControllerA has a blue background, ViewControllerB has a black background. Just to see which one is active.

So, in the implementation of myRootController, I do this:

// Implement viewDidLoad to do additional setup after loading the view, typically from a nib. - (void)viewDidLoad {     [super viewDidLoad];      ViewControllerA *vcA = [[ViewControllerA alloc] initWithNib];     [self.contentView addSubview:vcA.view];      [cvA release]; } 

By the way, the -initWithNib method looks like this:

- (id)initWithNib { // Load the view nib     if (self = [super initWithNibName:@"ViewA" bundle:nil]) {         // do ivar initialization here, if needed     }     return self; } 

That works. I see the view from ViewControllerA when I start the app. But now the big question is: A View Controller typically has all those methods like:

• (void)viewWillAppear:(BOOL)animated;
• (void)viewDidDisappear:(BOOL)animated;
• (void)viewDidLoad;

...and so on. Who or what, or how would those methods be called if I do it "my" way without a tab bar controller? I mean: If I allocate that ViewController's class and the view get's visible, would I have to take care about calling those methods? How does it know that viewWillAppear, viewDidDisappear, or viewDidLoad? I believe that the Tab Bar Controller has all this "cleverness" under the hood. Or am I wrong?

UPDATE: I've tested it. If I release the view controller (for example: ViewControllerA), I will get no log message on viewDidDisappear. Only when allocating and initializing the ViewControllerA, I get an viewDidLoad. But that's it. So all signs stand for the cleverness of UITabBarController now ;) and I have to figure out how to replicate that, right?

Answer 1

There's a nice example of switching views in Chapter 6 of Beginning iPhone Development. You can see the source code for it here: http://iphonedevbook.com/

SwitchViewController has the code to change views programatically.

 - (IBAction)switchViews:(id)sender {      if (self.yellowViewController == nil)     {         YellowViewController *yellowController = [[YellowViewController alloc]                 initWithNibName:@"YellowView" bundle:nil];         self.yellowViewController = yellowController;         [yellowController release];     }      [UIView beginAnimations:@"View Flip" context:nil];     [UIView setAnimationDuration:1.25];     [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];      UIViewController *coming = nil;     UIViewController *going = nil;     UIViewAnimationTransition transition;      if (self.blueViewController.view.superview == nil)      {            coming = blueViewController;         going = yellowViewController;         transition = UIViewAnimationTransitionFlipFromLeft;     }     else     {         coming = yellowViewController;         going = blueViewController;         transition = UIViewAnimationTransitionFlipFromRight;     }      [UIView setAnimationTransition: transition forView:self.view cache:YES];     [coming viewWillAppear:YES];     [going viewWillDisappear:YES];     [going.view removeFromSuperview];     [self.view insertSubview: coming.view atIndex:0];     [going viewDidDisappear:YES];     [coming viewDidAppear:YES];      [UIView commitAnimations];  }