Why can’t I force landscape orientation when use UINavigationController?

Best way to do this is the create extend UINavigationController and write your orientation function inside the extended class.

Class Declaration:

@interface MyNavigationControllerViewController : UINavigationController

@property(nonatomic, assign) UIInterfaceOrientation orientation;
@property(nonatomic, assign) NSUInteger supportedInterfaceOrientatoin;
@end

Implementation of MyNavigationController

@implementation MyNavigationController

@synthesize supportedInterfaceOrientatoin = _supportedInterfaceOrientatoin;

@synthesize orientation = _orientation;
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
        _supportedInterfaceOrientatoin = UIInterfaceOrientationMaskLandscape;
        _orientation = UIInterfaceOrientationLandscapeLeft;
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
- (BOOL)shouldAutorotate
{
    return YES;
}

-(NSUInteger)supportedInterfaceOrientations

{
    return _supportedInterfaceOrientatoin;
}

- (UIInterfaceOrientation)preferredInterfaceOrientationForPresentation
{
    return self.orientation;
}

@end

and use your extended like MyNavigationController as navigation controller to your rootviewcontroller.

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

@property (strong, nonatomic) ViewController *viewController;
@property (strong, nonatomic) MyNavigationControllerViewController *myNavController;

- (void) reloadAppDelegateRootViewControllerLandscape;
- (void) reloadAppDelegateRootViewController;
@end

So your application delegate didfinishlounchingwithoptions code will be as follow.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    self.viewController = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];

    self.myNavController = [[MyNavigationController alloc] initWithRootViewController:self.viewController];
    [self.myNavController setNavigationBarHidden:YES];
    self.window.rootViewController = self.myNavController;

    [self.window makeKeyAndVisible];
    return YES;
}

Only way you can provide different orientation for two different view with same navigation controller isto reload the navigation controller itself. So if you add two methods

- (void) reloadAppDelegateRootViewController{
    [[[UIApplication sharedApplication].delegate window] setRootViewController:nil];
    [(MyNavigationControllerViewController *)self.myNavController setOrientation:UIInterfaceOrientationPortrait];
    [(MyNavigationControllerViewController *)self.myNavController setSupportedInterfaceOrientatoin:UIInterfaceOrientationMaskAll];
    [[[UIApplication sharedApplication].delegate window] setRootViewController:self.myNavController];
}

- (void) reloadAppDelegateRootViewControllerLandscape{
    [[[UIApplication sharedApplication].delegate window] setRootViewController:nil];
    [(MyNavigationControllerViewController *)self.myNavController setOrientation:UIInterfaceOrientationLandscapeLeft];
    [(MyNavigationControllerViewController *)self.myNavController setSupportedInterfaceOrientatoin:UIInterfaceOrientationMaskLandscape];
    [[[UIApplication sharedApplication].delegate window] setRootViewController:self.myNavController];
}

and call these function after pushing and pop views.

Note:- I don’t know whether it is a good way or bad way.