iOS: Correct way to dispose of view controllers and go back to main screen

Question

I have a login screen, a second screen and a third screen. I want to have a button in the third screen to go back to the login screen and delete the current instances of second and third screen.

What I have is a push segue from login to second screen and a push segue from second to third screen. I've put a bar button item on the navigation bar of the third screen and attached a modal segue to it to go back to the login screen. On clicking I get a new login screen thats empty, this is just creating a new instance of it right? How do I delete the previous instances so that memory is saved? In Android we pass a flag FLAG_ACTIVITY_CLEAR_TOP to the intent that clears the other activities. Is there something analogous to this in iOS?

Answer 1

Instead of creating new object on third screen just use the following code inside navigation bar button action method. Ur remaining objects will be destroyed automatically.

[self.navigationController popToRootViewControllerAnimated:YES];

Answer 2

If you want to create a new instance of the Login View Controller and dispose all other controllers, your code should be like this.

   LoginViewController *loginController=[[UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil] instantiateViewControllerWithIdentifier:@"loginController"]; 
   UINavigationController *navController=[[UINavigationController alloc]initWithRootViewController:loginController];
   [[(AppDelegate*)[UIApplication sharedApplication].delegate window] setRootViewController:navController];

PS: If you do not mind keeping the same instance of LoginViewController you had before, then user2894531's answer is correct