Why Doesn't iOS Autorotate a View loaded from a Nib after it was released by didReceiveMemoryWarning?

Question

My iPad app makes heavy use of autorotation. This is great. However, I've noticed that if a hidden view is released by the default implementation of didReceiveMemoryWarning (as described here), when the view is re-loaded from the nib and I happen to be in landscape, it loads it in portrait. This wreaks havoc with the interface until I rotate the iPad manually and force it to go to the proper orientation.

I had assumed that iOS would load the view in the current orientation; that's what it does when the app launches. But it no, not after being unloaded by didReceiveMemoryWarning. Why not? And how can I get it to do that?

Prajna

Is the view outside of the view hierarchy (not a subview of the UIViewController view)? – Castorena

@dbarker - Nope, in fact it's the main view of the app. – Prajna

@dbarker Ah, but looking more carefully, I see that it's subviews of that view that are not properly rotated. Subviews included in the nib are properly rotated. Sort of. Hrm. Something might be up with my -willAnimateRotationToInterfaceOrientation:duration: method. Maybe it's not getting called because the rotation isn't animated? – Prajna

Yes, neither -willRotateToInterfaceOrientation:duration: nor -willAnimateRotationToInterfaceOrientation:duration: gets called. They're both called on app launch… – Prajna

Sounds right - the rotation callbacks won't get called when the view (re) loads. For the views that aren't managed by a nib, you'll need to adjust them manually to the orientation that UIViewController#interfaceOrientation returns. Not sure, but possible that this is what the nib does behind the scenes. – Castorena

Hrm. In what method should I do that? It's already done automatically on launch, so I'd need to be able to tell whether or not the view is loading on launch. – Prajna

That check should happen in viewDidLoad. If I'm understanding right, viewDidLoad is always orienting these views one way and the will/didRotate messages are correcting it (on launch) if it's wrong. Since there are cases where viewDidLoad happens and will/didRotate are not sent, viewDidLoad has to set these views up correctly for the current orientation. The will/didRotate messages will still handle further orientation changes. – Castorena

Yeah, that's what I figured; see answer below. Kind of annoying, though. Thanks for the help! – Prajna

Answer 1

The answer, determined thanks to pointers from dbarker, is that the view controller's rotation methods, including -willRotateToInterfaceOrientation:duration: and -willAnimateRotationToInterfaceOrientation:duration:, will not be called when a view is reloaded after a the default implementation of didReceiveMemoryWarning has unloaded the view. I've no idea why it would be different on app launch, but I do have a workaround

What I did was to set a boolean ivar, named unloadedByMemoryWarning, to YES in didReceiveMemoryWarning, like so:

- (void) didReceiveMemoryWarning {
    unloadedByMemoryWarning = YES;
    [super didReceiveMemoryWarning];
}

Then, in viewDidLoad, if that flag is true, I set it to NO and then call the rotation methods myself:

if (unloadedByMemoryWarning) {
    unloadedByMemoryWarning = NO;
    [self willRotateToInterfaceOrientation:self.interfaceOrientation duration:0];
    [self willAnimateRotationToInterfaceOrientation:self.interfaceOrientation duration:0];
    [self didRotateFromInterfaceOrientation:self.interfaceOrientation];
}

Kinda sucks that I have to do this, but it does work, and now I'm less concerned about getting killed by iOS for using too much memory.

Prajna

I am facing the same issue in my iPad app. This is kind of weird behavior but your solution helped me. – Tracy

Tried that solution but it's not doing it on my end unfortunately. Bleh... digs on – Tatum

Answer 2

1. I think iOS 5 might fix this.

2. For iOS 4.3, I've had good luck with another fix. After the load from nib:

   [parent.view addSubview:nibView];  
   nibView.frame = parent.view.frame;  
   [nibView setNeedsLayout];  
   

   If that worked, you could jettison the unloadedByMemoryWarning logic, since it's safe to do every load. Got the tip & code (basically) from here.

Ethnocentrism