Changing a UINavigationController’s Root View Controller

Posted by: Brian Knorr on: March 5, 2009

• In: IPhone Development
• 24 Comments

If you have ever dealt with using a UINavigationController in your iPhone app, you may have wanted to swap out the root view controller with a new one. Unfortunately the iPhone SDK doesn’t allow you to do this. To do so you actually have to create a brand new UINavigationController, which for us was not acceptable.

To support swapping out the root view controller, we created a custom class that extends UINavigationController and adds a method “setRootViewController”. We do a little hack by creating a generic UIViewController and setting it as a fake root view controller at index 0. This allows you to push and pop UIViewControllers above it on the stack. So now the “perceived” root view controller is always at index 1 behind the scenes, but actually appears to be at index 0. It behaves exactly as the original UINavigationController except that now you can change the “perceived” root view controller. Here is an example of using it:

//Say you have a UIViewController that 
//handles logging in to your app
self.loginViewController = [LoginViewController loginViewController];

//Here we initialize it as the root view controller
//of your main navigation
self.mainNav = [[[TVNavigationController alloc] initWithRootViewController:loginViewController] autorelease];

//Let's say the user interacts with the screen and logs 
//in and now you want to replace the login view controller 
//with the UIViewController that is your application

self.appViewController = [AppViewController appViewController];
//Now we call the new method that let's you set 
//the root view controller 
[mainNav setRootViewController:appViewController];

Below is the code to make all this work:

//// Header file

@interface TVNavigationController : UINavigationController {
  UIViewController *fakeRootViewController;
}

@property(nonatomic, retain) UIViewController *fakeRootViewController;

-(void)setRootViewController:(UIViewController *)rootViewController;

@end

//// Implementation file

#import “TVNavigationController.h”

@implementation TVNavigationController

@synthesize fakeRootViewController;

//override the standard init
-(id)initWithRootViewController:(UIViewController *)rootViewController {
  //create the fake controller and set it as the root
  UIViewController *fakeController = [[[UIViewController alloc] init] autorelease];
  if (self = [super initWithRootViewController:fakeController]) {
    self.fakeRootViewController = fakeController;
    //hide the back button on the perceived root
    rootViewController.navigationItem.hidesBackButton = YES;
    //push the perceived root (at index 1)
    [self pushViewController:rootViewController animated:NO];
  }
  return self;
}

//override to remove fake root controller
-(NSArray *)viewControllers {
    NSArray *viewControllers = [super viewControllers];
	if (viewControllers != nil && viewControllers.count > 0) {
		NSMutableArray *array = [NSMutableArray arrayWithArray:viewControllers];
		[array removeObjectAtIndex:0];
		return array;
	}
	return viewControllers;
}

//override so it pops to the perceived root
- (NSArray *)popToRootViewControllerAnimated:(BOOL)animated {
    //we use index 0 because we overrided “viewControllers”
    return [self popToViewController:[self.viewControllers objectAtIndex:0] animated:animated];
}

//this is the new method that lets you set the perceived root, the previous one will be popped (released)
-(void)setRootViewController:(UIViewController *)rootViewController {
    rootViewController.navigationItem.hidesBackButton = YES;
    [self popToViewController:fakeRootViewController animated:NO];
    [self pushViewController:rootViewController animated:NO];
}

- (void)dealloc {
    self.fakeRootViewController = nil;
    [super dealloc];
}

@end

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Tags: iphone