ViewWillAppear not getting called in modal controller. What is wrong here?

I have seen a couple of articles about ViewWillAppear and ViewDidAppear not firing under certain circumstances but I'm still wondering what the thinking behind the behavior is and how I can work around it in my specific case.

• window has one view which is handled by a deafult UIVieController and contains a button.
• Clicking the button presents another view controller modally (VC_MAIN).
• Depending on settings, the modally shown view controller (VC_MAIN) will either present view A or view B.
• View A and B ar开发者_C百科e handled by different view controllers (VC_A and VC_B).
• None of the ViewWill* or ViewDid* methods is called in VC_A or VC_B.
• I can work around it by calling them manually in VC_MAIN in the corresponding ViewDid* and ViewWill* methods. But if VC_MAIN decides to switch from VC_A to VC_B this does not help. VC_MAIN's View* methods won't be called again and neither will VC_A's or VC_B's.

I could of course dimiss VC_MAIN when switching from A to B, but I don't want to. I want to animate the switching and not just open another modal view.

Why the heck don't those methods get called? It really is beyond me! If you look at UISplitViewController: it houses two sub controllers, which can show other controllers. They basically do the same as I'm trying to do. Has Apple placed kludges all over the code?

My experience with this kind of issue:
If you have a view controller VC managing a main view V and this view has a subview V' managed by another view controller VC', viewWillAppear: and other methods like willRotateToInterfaceOrientation: are not sent to VC'.

What you could to is manually forward these calls from VC:

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    [mySubViewController viewWillAppear:animated]; // VC'
}

(Note: I'm not familiar with MonoTouch so I answered with ObjC code)

EDIT

It reminded me that the View Controller Programming Guide states clearly:

Each custom view controller object you create is responsible for managing all of the views in a single view hierarchy. [...] The one-to-one correspondence between a view controller and the views in its view hierarchy is the key design consideration. You should not use multiple custom view controllers to manage different portions of the same view hierarchy.

What I would guess as a reason is the step between

Depending on settings, the modally shown view controller (VC_MAIN) will either present view A or view B.

View A and B are handled by different view controllers (VC_A and VC_B).

If you read the introduction in the view controller programming guide from Apple, they recommend only having one view controller per screen, even if it manages multiple views or a hierarchy of subviews. It would probably be better to manage the views A and B directly in the VC_MAIN, then you would get the notifications you need. If you for any reason preffer the way of having separate view controllers, you might have to notify them by yourself.

You should really manually call those methods. Its a custom way of managing and showing VC views, so its up to you to determine when each sub-viewcontroller receives the lifecycle calls. In VC_MAIN, create a showVC:newVc method that will call

[newVc viewWillAppear]
[mainView addSubview:newVc.view]
[newVc viewDidAppear]

similarly, create a hideVC: that will call viewWill/DidHide

on your VC_Main viewWillAppear, call the showVC method apropriatelly based on the current config, and everytime you switch your views, the methods will be correctly called.

Its an old question, that was partially handled on iOS5 but still works fine in this fashion, and is fully backwards compatible up to iOS3.