How to set Root View Controller programatically in Objective C?

Question

I am a newbie in iOS Development trying to learn how to create and set views programmatically.

i am trying to do swift statement in Obj-C

window?.rootViewController = UINavigationController(rootViewController : ViewController()) 

Project: Single View Application . Trying to link default Created ViewController.h

As per Krunals Answer i updated code but Navigation Controller is not shown in simulator

Cmd+Click on controller does not navigate to ViewController File

#import "AppDelegate.h"
#import "ViewController.h"

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
UIScreen *screen=[[UIScreen alloc]init];
    UIWindow *window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

    self.window.makeKeyAndVisible;




    ViewController *controller = [[ViewController alloc] init];



    window.rootViewController = [[UINavigationController alloc] initWithRootViewController:controller] ;

Answer 1

Initialise your view controller ViewController before you add (use as root controller of navigation) into navigation controller stack.

Here is sample code to initialise simple view controller

UIViewController *controller = [[UIViewController alloc] init];

Here is sample code to initialise using storyboard

ViewController *controller = [[UIStoryboard storyboardWithName:@"Main" bundle:nil] instantiateViewControllerWithIdentifier:@"<ViewController - string identifier of your view controller>"];

Here is sample code to initialise using NIB/Bundle

ViewController *controller = [[ViewController alloc] initWithNibName:@"<ViewController - string NIB name>>" bundle:nil];

According to your code and following comment try this code only (remove other codes from your app delegate launch):

// make sure your NIB name is 'ViewController' 

ViewController *controller = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
if (controller != nil) {
    self.window.rootViewController = [[UINavigationController alloc] initWithRootViewController: controller];
    self.window.makeKeyAndVisible;
} else {
   //print - your view controller is nil
}

Answer 2

Thanks to Krunal for detailed answer .

Thanks to dan for support

i found issue instead of self.window.rootViewController , i typed window.rootViewController.

setting self.window.rootViewController solved issue.

i dont know difference between self.window.rootViewController and window.rootViewController and reason for issue.

If some one knows answer please provide answer on comment

#import "AppDelegate.h"
#import "ViewController.h"


@interface AppDelegate ()

@end

@implementation AppDelegate


- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    UIScreen *screen=[[UIScreen alloc]init];
    UIWindow *window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];


    self.window.makeKeyAndVisible;




    ViewController *controller = [[ViewController alloc] init];





    self.window.rootViewController = [[UINavigationController alloc] initWithRootViewController:controller] ;