What is the perfect way to make a logout from IOS app?

Question

The below code is working but has a bug. The scenario is that, I begin by logging in to enter the app system. Once the login has succeeded, the app will set UserDefaults (UserId). After that, I can navigate the app views with stored UserId. Once I go to settings and tab logout, that will clean UserId and go to login view.

The BUG: When I login again to the app and click the home button to go to iPhone desktop and close the app, and return to open it again it still storing the UserId. So, if I go to the setting and log out that will clean UserId and will not go to login view. I don't know why.

The code:

- (IBAction)resetKeychain:(id)sender {

    UIActionSheet *actionSheet = [[UIActionSheet alloc] 
                 initWithTitle:@"Are you sure you want to logout?" 
                 delegate:self 
                 cancelButtonTitle:@"Cancel" 
                 destructiveButtonTitle:@"Logout"
                 otherButtonTitles:nil];
    actionSheet.actionSheetStyle = UIActionSheetStyleDefault;
    [actionSheet showFromTabBar:self.tabBarController.tabBar];
    [actionSheet release];

}

- (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex {
    if (buttonIndex ==0) {
        //logout
        NSUserDefaults * defaults = [NSUserDefaults standardUserDefaults];
        //delete user ID fro user Defaults
        [defaults setObject:nil forKey:@"UserId"];
        //redirect to login view

        NewClassMoonAppDelegate * appsDelegate =[[UIApplication sharedApplication] delegate];
        [appsDelegate.window addSubview:[appsDelegate.login view]];

    }
}

Answer 1

From what I can interpret from you question, which needs to be formatted and made coherent by the way, I believe that:

a) your @"UserID" value is not syncing with NSUserDefaults because you are not calling the -synchronize method. NSUserDefaults will update its in-memory key-value store, but will not write it to disk meaning that it's lost at an arbitrary time.

b) The fact that it is not going to the loginView could be to do with any few reasons, most likely that it is already a subview of your UIWindow. So, instead of reusing the login property in your app delegate, create a new instance variable of the View Controller, and set that as the rootViewController instead.

- (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex {

    if (buttonIndex == 0) {
        NSUserDefaults * defaults = [NSUserDefaults standardUserDefaults];
        [defaults setObject:nil forKey:@"UserId"];
        [defaults synchronize];
        //redirect to login view

        NewClassMoonAppDelegate * appsDelegate =[[UIApplication sharedApplication] delegate];
        LoginViewController *login = [[LoginViewController alloc] initWithNibName...];
        [appsDelegate.window setRootViewController:nil];
        [appsDelegate.window setRootViewController:login];

    }
}

Answer 2

Swift:

From max_'s answer with some changes:

let objectsToSave: [String] = [obj1, obj2, obj3]
for key in objectsToSave {
    NSUserDefaults.standardUserDefaults().removeObjectForKey(key)
}

 let appsDelegate = UIApplication.sharedApplication().delegate
 let storyboard = UIStoryboard(name: "MainStoryboard", bundle: nil)
 let newLoginVC: LoginViewController = storyboard.instantiateInitialViewController() as! LoginViewController
 appsDelegate?.window!!.rootViewController = nil
 appsDelegate?.window!!.rootViewController = newLoginVC

EDIT: The only changes I've made are just that I initialize newLoginVC through Storyboards instead of initWitName.