show mainviewcontroller from another view

how can I show mainviewcontroller from another view, on my existing project?
i dont want to create the view from the delegate with this code.
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
MainViewController *viewController = [[MainViewController alloc] init];
UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:viewController];
navController.toolbarHidden = NO;
[[self window] setRootViewController:navController];
// Override point for customization after application launch.
self.window.backgroundColor = [UIColor whiteColor];
[self.window makeKeyAndVisible];