pushViewController and presentViewController are not working.

@interface ViewController ()@end@implementation ViewController- (void)viewDidLoad{    [super viewDidLoad];// Do any additional setup after loading the view, typically from a nib.    //self.view.backgroundColor=[UIColor purpleColor];        UIButton *btn=[UIButton buttonWithType:UIButtonTypeRoundedRect];    btn.frame=CGRectMake(60, 200, 140, 40);    [btn setTitle:@"Button" forState:UIControlStateNormal];    [btn addTarget:self action:@selector(buttonAction) forControlEvents:UIControlEventTouchUpInside];    [self.view addSubview:btn];}//-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{//    if([segue.identifier isEqualToString:@"segueId"]){//        //        DetailViewController *detailVC=segue.destinationViewController;//        detailVC.text=@"Segue Value";//        detailVC.delegate=self;//    }//}#pragma mark - ChangeLabelTextDelegate-(void)changeText:(UIViewController *)viewController text:(NSString *)textValue{    self.mainLabel.text=textValue;    }-(void)buttonAction{    UIStoryboard *storyboard=[UIStoryboard storyboardWithName:@"Main" bundle:nil];    DetailViewController *detailVC=[storyboard instantiateViewControllerWithIdentifier:@"detailView"];    detailVC.text=@"pushViewController";    detailVC.delegate=self;    [self.navigationController pushViewController:detailVC animated:YES];        // Two method.    //[self performSegueWithIdentifier:@"segueId" sender:self];        /* One method.    UIStoryboard *storyboard=[UIStoryboard storyboardWithName:@"Main" bundle:nil];    DetailViewController *detailVC=[storyboard instantiateViewControllerWithIdentifier:@"detailView"];        detailVC.text=@"Hello World!!";    [self presentViewController:detailVC animated:YES completion:^{        NSLog(@"Call Back...");    }];    */}- (void)didReceiveMemoryWarning{    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.    }@end