Why is self.navigationController nil in a storyboard application?

Question

I have an iOS storyboard-based application which uses the navigationController to control the view transitions. The app delegate's didFinishLaunchingWithOptions is:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"StoryboardPrincipal"  bundle:[NSBundle mainBundle]];
    self.viewController = [storyboard instantiateInitialViewController];
    // Instantiate a UIWindow object and initialize it with the screen size of the iOS device
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    self.window.rootViewController = self.viewController;
    [self.window makeKeyAndVisible];
    return YES;

}

In the initial view, pushed by the initial navigation controller, I push the next view like:

 [[UIStoryboard storyboardWithName:@"StoryboardPrincipal" bundle:nil] instantiateViewControllerWithIdentifier:@"ViewControllerUsuario"];
 self.ViewUsuarioVIP = [self.storyboard instantiateViewControllerWithIdentifier:@"ViewControllerUsuario"];          
 self.navigationController.navigationBar.hidden = NO;
 self.navigationController.navigationBar.barStyle = UIBarStyleBlackTranslucent;
 [self.navigationController pushViewController:self.ViewUsuarioVIP animated:YES];

Although the next view is successfully pushed, self.navigationController is nil and the navigation bar does not appear.

//
//  ViewController.h


#import <UIKit/UIKit.h>
#import "PageControl.h"
#import "ViewUsuario.h"
#import "SaibaMaisViewController.h"
#import "WebService.h"
#import "ViewCaptainViewController.h"


@interface ViewController : UIViewController <UIScrollViewDelegate, PageControlDelegate, UITextFieldDelegate> {
    IBOutlet UIScrollView *_scrollView;
    IBOutlet PageControl *_pageControl;
    IBOutlet UIImageView *leftArrow;
    IBOutlet UIImageView *rightArrow;

    }
@property (nonatomic, retain) IBOutlet UIScrollView *_scrollView;
@property (nonatomic, retain) IBOutlet UIScrollView *_imageScrollView;
@property (nonatomic, retain) IBOutlet PageControl *_pageControl;
@property (nonatomic, retain) IBOutlet UIImageView *leftArrow;
@property (nonatomic, retain) IBOutlet UIImageView *rightArrow;
@property (nonatomic, retain) ViewUsuario *ViewUsuarioVIP;
@property (nonatomic, retain) ViewCaptainViewController *ViewCaptainVIP;
@property (strong, nonatomic) SaibaMaisViewController *SaibaMaisViewControllerVIP;
@property (strong, nonatomic) WebService *WebServiceVIP;
@property (strong, nonatomic) NSString *firstname;
@property (strong, nonatomic) NSString *id;
@property (strong, nonatomic) NSString *lastname;
@property (strong, nonatomic) NSString *type;
@property (strong, nonatomic) NSString *photo;


@end

I tried to post a image with the storyboard but I am not allowed to do so. But, the Navigation Controller is the RootView. The ViewUsaruio declaration is:

//
//  ViewUsuario.h
//  FlyVIP
//

#import <UIKit/UIKit.h>
#import "NovoVoo.h"
#import "VoosExistentesTableViewController.h"
#import "VooAbertosViewController.h"

@interface ViewUsuario : UIViewController;
@property (nonatomic, retain) NovoVoo *NovoVooVIP;
@property (nonatomic, retain) VoosExistentesTableViewController *VoosExistentesVIP;
@property (nonatomic, retain) VooAbertosViewController *VoosAbertosVIP;
@property (strong, nonatomic) NSString *firstname;
@property (strong, nonatomic) NSString *id;
@property (strong, nonatomic) NSString *lastname;
@property (strong, nonatomic) NSString *type;
@property (strong, nonatomic) NSString *photo;


@end

Answer 1

You also need to explain the structure of your storyboard, and the header of your ViewControllerUsuario view controller. Where have you defined a navigation controller in your storyboard?

If you want to have a navigation controller as the root view controller for your storyboard, you have to define one in the storyboard. One is not created for free. Note that if you create a storyboard with any other view controller as the root then you can select "embed in" from the editor menu. That will change the root view controller to a navigation controller and make the previous view controller the first child of the navigation controller.

Answer 2

Many times, your app acting strange in the iOS simulator is just XCode being weird.

Quit XCode entirely, then run your app again.

If this persists, you have a problem with how you've set the storyboard up. Most likely your view controller is not embedded within a navigation controller in the storyboard.

I like this tutorial as it has easy to follow examples and many screenshots.

Answer 3

我有同样的问题...您可以使用getter方法简单地引用它，即：

[self navigationController]