Objective-C：模态搜索和发布视图控制器

Question

The initial view controller on my app is a UITabBarController that displays for logged in users.

For new users, however, my app delegate will point them to a login/registration view controller first:

// New user, show login
self.window.rootViewController = [self.window.rootViewController.storyboard instantiateViewControllerWithIdentifier:@"LoginViewController"];

When the user has completed the login/registration, I then send the user to the tabbar as such:

// Login done, go to main view
[self performSegueWithIdentifier:@"userLoginToMainSeg" sender:self];

However, doing it this way, the LoginViewController is not released (dealloc is not called).

Can someone explain the error in my logic here?

Answer 1

Your modal segue is basically doing:

[loginViewController presentViewController:mainViewController animated:YES completion: ...];

What this means is that mainViewController becomes loginViewController s presentedViewController :

loginViewController.presentedViewController == mainViewController
mainViewController.presentingViewController == loginViewController

When you're presenting a view controller , the presenting view controller remains in the view controller hierarchy, so that you can later navigate back by calling:

[loginViewController dismissViewControllerAnimated: ...];

So it's perfectly normal that loginViewController is not released, since it's still the window's rootViewController . It's only that loginViewController is obstructed by the presented mainViewController .

If you want to eradicate loginViewController you can set window.rootViewController directly, but that wouldn't animate the transition. You can achieve animation by messing around the view controllers' views , but it's kind of outside the officially sanctioned territory...

IMO the cleanest solution would be to implement a basic container view controller that would be your window's rootViewController , and that could orchestrate the transition between loginViewController and mainViewController by animating their views, and then throwing away loginViewController . It would be kind of a primitive navigation controller without a navigation bar and a navigation stack – just swapping the current view controller with the new one, and throwing away the former.