CODEWITHSUNDEEP
iosswiftauthenticationviewcontrollertwitterkit
undervine
undervine

Reputation: 59

Swift - Why should I use viewDidAppear rather than viewWillAppear when redirect user if the user logged in already

I'm making twitter client app, using TwitterKit.

The initial VC is loginVC with login button. After login, it presents tableviewVC that shows list of tweets.

I want to redirect the user to tableviewVC directly if the user logged in already before and the session remains.

So I implemented codes in viewWillAppear that check logged-in users and present tableviewVC, but the tableviewVC never presented though the user session remains.

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    if TWTRTwitter.sharedInstance().sessionStore.hasLoggedInUsers() {
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let tweetVC = storyboard.instantiateViewController(withIdentifier: "TweetTableViewController")
        present(tweetVC, animated: true, completion: nil)
    }
}

But when I implemented the same codes in viewDidAppear, the tableviewVC showed up when the user session remains.

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    if TWTRTwitter.sharedInstance().sessionStore.hasLoggedInUsers() {
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let tweetVC = storyboard.instantiateViewController(withIdentifier: "TweetTableViewController")
        present(tweetVC, animated: true, completion: nil)
    }
}

I don't understand why it doesn't work when the codes are in viewWillAppear.

Could someone please explain it for me?

Upvotes: 0

Views: 931

Answers (2)

rickrvo
rickrvo

Reputation: 565

I think it's because it's the initial VC that the app is still presenting, and viewWillAppear is called before the view is presented. So trying to present another view on top a view that's not presented yet won't work.

My solution to this was to load the Login view with the loginButton hidden then on viewDidAppear check if user is logged in then present the logged page otherwise you show the loginButton.

Upvotes: 0

Pramod Kumar
Pramod Kumar

Reputation: 2652

As the methods name explains,

viewWillApper means the view of the current viewController is going to be appear, still not on the window. So, in that case you cann't present the any viewController over the viewController which is not being displayed in the window.

viewDidApper means the view of the current viewController is being displayed on the window, That's why you're able to present the new viewController.

PS: As you want to achieve, in case of already logged in show the listVC. I would suggest to setup the rootViewController of the window in didFinishLaunchingWithOptions method of AppDelegate.

Like: 

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

    var rootVC: UIViewController?
    if <check weather user is already logged in> {
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        rootVC = storyboard.instantiateViewController(withIdentifier: "TweetTableViewController")
    }
    else {
        rootVC = <you loginVC object>
    }

    self.window?.rootViewController = rootVC
    self.window?.makeKeyAndVisible()


    return true
}

Upvotes: 1

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