如何卸载菜单（UIViewControllers）

Question

I'm working on an app with which I send and receive data from and to a database.

At the moment, when I start the app in portrait or landscape position, it will always display the first menu in portrait style. When I turn the first menu, it switches to landscape just fine. I have properties in my AppDelegate to store screen width and height.

Whenever I navigate to another menu for the first time, it takes the screen width and height from the AppDelegate to draw the new menu. Every menu I navigate to does this perfectly.

The problem is, that when a menu is already loaded, I switch to another menu, turn the screen and go back to the previous menu, the layout is still in the previous screen mode. For example:

1. I start the app and get to the first menu in portrait mode. The values for screen width and height in the AppDelegate will change to the current view.bounds.
2. I navigate to menu #2 for the first time. Menu #2 will use the screen width and height in the AppDelegate to draw the menu.
3. I navigate to menu #3 for the first time. Just like Menu #2, it takes the screen width and height from the AppDelegate to draw the menu.
4. I turn the menu from portrait to landscape. Menu #3 will redraw and change the screen width and height in the AppDelegate to the new values.
5. I navigate back to menu #2, but it's still drawn as if it were in portrait mode.

Is there a way to unload the menu (that's not the obsolete method of "WillUnload" or "DidUnload")? Or is there a method that gets called every time I navigate to a menu that I already loaded in my memory?

I love to hear from you.

Love and regards, Björn

Answer 1

• viewWillAppear: method gets invoked every time the controller's view is about to be displayed. Whenever you make a transition to and fro from a controller, it would be invoked.

  From Apple's documentation( iOS Developer Library ) :

  This method is called before the receiver's view is about to be added to a view hierarchy and before any animations are configured for showing the view. You can override this method to perform custom tasks associated with displaying the view. For example, you might use this method to change the orientation or style of the status bar to coordinate with the orientation or style of the view being presented. If you override this method, you must call super at some point in your implementation.

• An another lifecycle method that you can use is viewWillLayoutSubviews . You can read more about it here.( iOS Developer Library )