Programming iOS: clarifications about Root View Controller

Question

Through this question I would like to know if I understand well the notion of Root View Controller.

In iOS application, the Root View Controller (RVC) is the control

Answer 1

Ya.. when I began iPhone dev.. the rootViewController thing threw me for a loop too. But it’s really straight forward.

when the app starts, I create a UIWindow object in my app delegate class. Also, in that class, I have a property of type UIWindow called window;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {  

    UIWindow *w = [[UIWindow alloc]initWithFrame:[[UIScreen mainScreen]bounds]];
    self.window=w;
    [w release];
    // other code here...
}

I then create a UIViewController whose view will be the first view in the window hierarchy, this could be called the "root view controller".

The confusing part is...that often we create a UINavigationController as the "root view controller" and that navigation controller has an init method that asks for a "RootViewController", which is the first viewcontroller it will place on its stack.

So, the window gets a "root view controller", which is the UINavigationController, which also has a RootViewController, which is the first view controller you want to show.

once you sort that out, its all makes sense.. I think :-)

here is some code that does it all.. (taken from a project I have open in front of me)

//called with the app first loads and runs.. does not fire on restarts while that app was in memory
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    


    //create the base window.. an ios thing
    UIWindow *w = [[UIWindow alloc]initWithFrame:[[UIScreen mainScreen]bounds]];
    self.window=w;
    [w release];

    // this is the home page from the user's perspective
    //the UINavController wraps around the MainViewController, or better said, the MainViewController is the root view controller
    MainViewController *vc = [[MainViewController alloc]init];

    UINavigationController *nc = [[UINavigationController alloc]initWithRootViewController:vc];
    self.navigationController=nc;  // I have a property on the app delegate that references the root view controller, which is my navigation controller.

    [nc release];
    [vc release];

    //show them
    [self.window addSubview:nc.view];
    [self.window makeKeyAndVisible];

    return YES;
}