i have a problem in objective c project 
there is a button at the viewcontroller and when i click the button pushviewcontroller doesnt work.

my appdelegate.m file :

- (BOOL)application UIApplication *)application didFinishLaunchingWithOptions NSDictionary *)launchOptions {
    self.window = [[UIWindow alloc] initWithFrame:EK_SCREEN_BOUNDS];

    ExampleViewController *exampleViewController = [ExampleViewController new];
    self.window.rootViewController               = exampleViewController;
    [self.window makeKeyAndVisible];

    return YES;

Button click method (in ExampleViewController):

        mainViewController *frm = [mainViewController new];
        [self.navigationController pushViewController:frm animated:YES];

How i can fire button click event ?