self.navigationController is null - iphone

Question

in my viewcontroller,I have a button,when press the button,entry the navigationController,my code like:
-(IBAction)ShangHaiButtonPressed:(id)sender{
marketviewcontroller = [[MarketViewController alloc]initWithNibName:#"MarketViewController" bundle:nil];
NSLog(#"%#",self.navigationController);
[self.navigationController pushViewController:marketviewcontroller animated:YES];
[marketviewcontroller release];
}
but I can see the self.navigationController is null,how to solve this problem?thank you.
update:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
_switchviewcontroller = [[SwitchViewController alloc]initWithNibName:#"SwitchViewController" bundle:nil];
[self.window addSubview:_switchviewcontroller.view];
[self.window makeKeyAndVisible];
return YES;
}

Answer 1

The navigationController property of a view controller will return a valid navigation controller object only if the view controller is in a navigation controller's navigation stack. A view controller can be added to a navigation stack in the following ways.
By making the view controller the rootViewController of a navigation controller using initWithRootViewController: method of UINavigationController
By pushing the view controller using pushViewController: method of UINavigationController.
Make sure your view controller is added to the navigation stack in any of the above ways.
EDIT: (After the didFinishLaunchingWithOptions: code added to the question):
Change the didFinishLaunchingWithOptions: method to this,
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
_switchviewcontroller = [[SwitchViewController alloc]initWithNibName:#"SwitchViewController" bundle:nil];
UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:_switchviewcontroller];
[self.window addSubview:navController.view];
[navController release];
[self.window makeKeyAndVisible];
return YES;
}
Swift 4 (version):
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey : Any]? = nil) -> Bool {
switchviewcontroller = SwitchViewController(nibName: "SwitchViewController", bundle: nil)
let navController = UINavigationController(rootViewController: switchviewcontroller)
window.addSubview(navController.view)
window.makeKeyAndVisible()
return true
}

Answer 2

This code will yield the solution you're looking for:
-(IBAction)ShangHaiButtonPressed:(id)sender {
UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:self];
[self.view removeFromSuperview];
[appDelegate.window addSubview:nav.view]; // appDelegate is the delegate of your Application
marketViewController = [[MarketViewController alloc] initWithNibName:#"MarketViewController" bundle:nil];
[nav pushViewController:marketViewController animated:YES];
[marketViewController release];
}

Answer 3

In AppDelegate.m file make your first view RootView for Navigation :
-(BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
myView *Obj=[[myView alloc]initWithNibName:#"myView" bundle:nil];
UINavigationController *nav = [[UINavigationController alloc]initWithRootViewController:Obj];
nav.navigationBar.barStyle = UIBarStyleBlackOpaque;
[window addSubview:nav.view];
[self.window makeKeyAndVisible];
return YES;
}
In your myView.m file add below code to navigate to myNewView from myView :
-(void) registerMethod {
myNewView *obj = [[myView alloc] initWithNibName:#"myNewView" bundle:nil];
[self.navigationController pushViewController:obj animated:YES];
[obj release];
}