gistfile1.m

// HomeTableViewController

- (IBAction)btnLogout:(id)sender {
    
    self.animateBOOL = YES;
    [Lockbox setString:@"FALSE" forKey:kLoggedinStatusKeyString];
    [(TabBarViewController *)[self tabBarController] loginCheck:animateBOOL];
}

// TabBarViewController

- (void)loginCheck:(BOOL)animateBOOL
{
    UIStoryboard *mainstoryboard = self.storyboard;
    LoginViewController* loginViewController = [mainstoryboard instantiateViewControllerWithIdentifier:@"LoginViewController"];
    
    if ([[Lockbox stringForKey:kLoggedinStatusKeyString] isEqualToString:@"FALSE"]) {
        [self presentViewController:loginViewController animated:animateBOOL completion:nil];
    }
}