objective C Basic question

Question

hi friends, i made a simple application using view based template.and i put only nslog inside view didload method in viewController file and also inside applicationDidFinishLaunch method (in appDelegate )to checked which class file called first.

after the run i got: viewController Run first and then appdelegate ..but i think appdelegate should first then other's called according to the need ... plz give me the proper reasion.

Noted that --i did not call viewController (didnot make object) in my appDelegate(inside application didFinishLaunch) . i am using ios4

Answer 1

If your View Controller is a property of the AppDelegate, similar to the code reference

@interface AppDelegate_Shared : NSObject <UIApplicationDelegate, UIAlertViewDelegate, OMFDataLoadDelegate> {

    NSManagedObjectModel *managedObjectModel;
    NSManagedObjectContext *managedObjectContext;       
    NSPersistentStoreCoordinator *persistentStoreCoordinator;

    UIWindow *window;

    UITabBarController *tabBarController;

}

then it is probably getting allocated by the AppDelegate when it is being allocated. According to the Apple documentation viewDidLoad is run after the view is loaded into memory, which can be a little confusing, since the language can make you believe it's when it's loaded onto the screen.

http://developer.apple.com/iphone/library/documentation/uikit/reference/UIViewController_Class/Reference/Reference.html#//apple_ref/doc/uid/TP40006926-CH3-SW25

Move your NSLog statement to viewDidAppear for the result you were expecting. Here's two sample snippets with the way you should expect the statements to load.

ViewController.m

- (void) viewDidLoad {
  NSLog(@"1st - this occurs when appDelegate allocates this object");
}
- (void) viewDidAppear {

  NSLog(@"3rd - this should appear after the applicationDidFinishLaunchingStatement");
}

AppDelegate_Shared.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    
    NSLog(@"2. Starting AppDelegate_Shared");

    [window addSubview:self.tabBarController.view];
    [window makeKeyAndVisible];

    NSLog(@"4. Leaving AppDelegate_Shared");
    return YES;
}

Answer 2

If the initial view hasn't loaded then clearly the application has not finished launching.

The messages are sent in the right order.