How to switch from one UIViewController to another? - iphone

Question

I have a problem with switching from one viewcontroller to another.
Here is what I have :
In my "AppDelegate_iPad.m" :
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
CGRect frame = [UIScreen mainScreen].bounds;
window = [[UIWindow alloc] initWithFrame:frame];
window.backgroundColor = [UIColor blackColor];
LoginViewController_iPad *loginView = [[LoginViewController_iPad alloc] initWithNibName:#"LoginViewController_iPad" bundle:nil];
[window addSubview:loginView.view];
[self.window makeKeyAndVisible];
return YES;
}
That works. Now I have a login button on that screen and when pressed it calles this :
- (IBAction)doPressLoginButton
{
DebugLog(#"doPressLoginButton");
MenuViewController_iPad *menuView = [[MenuViewController_iPad alloc] initWithNibName:#"MenuViewController_iPad" bundle:nil];
[self.navigationController pushViewController:menuView animated:YES];
[menuView release];
}
The problem is that nothing happends. I assume I am missing the actual navigationconroller ?!
Hope that anyone can help.
Thank you

Answer 1

You should create a UINavigationController instance variable in your app delegate. Then, make sure you synthesize it and release it in your dealloc method.
Your implementation of application:didFinishLaunchingWithOptions: could look like this:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
// window is usually an IBOutlet
CGRect frame = [UIScreen mainScreen].bounds;
window = [[UIWindow alloc] initWithFrame:frame];
window.backgroundColor = [UIColor blackColor];
LoginViewController_iPad *loginView = [[LoginViewController_iPad alloc] initWithNibName:#"LoginViewController_iPad" bundle:nil];
navigationController = [[UINavigationController alloc] initWithRootViewController:loginView];
[loginView release];
[self.window addSubview:navigationController.view];
[self.window makeKeyAndVisible];
return YES;
}
Now you'll be able to use self.navigationController.

Answer 2

I assume I am missing the actual navigationconroller ?!
you are right. :D
self.navigationController returns nil if you don't set up an NavigationController.
And any messages send to nil object will be ignored.
If you only need switch from one to another.
using
[self presentModalViewController:modalViewController animated:YES];
instead.