iPhone dev - viewDidLoad and viewDidUnload in programmatically created view?

Question

I read somewhere that in a programmatically created view in a UIViewController, not using Interface Builder, -viewDidLoad and -viewDidUnload should not be used. Is this right? Why? Where would I release subviews that I have retaining properties of? Or should I just not use properties for them?

EDIT: Read my comments on Rob Napier's answer.

Answer 1

viewDidLoad and viewDidUnload are only called automatically for you if you use a NIB. If you're not using a NIB, then it's your responsibility to decide when to create and destroy your subviews. If you're doing it programmatically, you don't need what these methods provide (a hook for when the NIB loading system does it automatically).

You should be creating your subviews in loadView. You should be releasing things in dealloc, didReceiveMemoryWarning and viewWillDisappear. Of course, you have some flexibility here. If it's a particularly small view, or you need it a lot, you could choose to just release things in dealloc.

A good resource for best practices around when to allocate and release is Managing Memory Efficiently.

Answer 2

Create your subviews in -viewDidLoad. If you need ivars for them then only assign their values. The reference is hold by adding the views as subviews to you main view.

Then when your view is unloaded you should set your ivars to nil, because the object have been released since your view was removed and released.

So in your header

@interface MyViewController : UIViewController {
  IBOutlet UIView *someSubview; // assigned
}
@property (nonatomic, assign) IBOutlet UIView someSubview;
@end

And in your implementation

@implementation MyViewController
//... some important stuff

- (void)viewDidLoad;
{
  [super viewDidLoad];
  someSubview = [[UIView alloc] initWithFrame:self.view.bounds];
  [self.view addSubview:someSubview]; // retains someSubview
  [someSubview release];   // we don't hold it
}

- (void)viewDidUnload;
{
  [super viewDidUnload];
  someSubview = nil;  // set the pointer to nil because someSubview has been released
}

//... more important stuff

@end

If you wish you can also not release someSubview in -viewDidLoad, but then you have to release it in -viewDidUnload AND -dealloc since (if I remember right) -viewDidUnload isn't called before -dealloc. But this isn't necessary if you don't retain someSubview.