Question

I have a simple navigation hierarchy:

Controller 1 > Controller 2 > Controller 3

Each controller contains a reference (@property (nonatomic, assign) ...) to it’s child and parent.

My viewWillDisappear looks something like this:

- (void)viewWillDisappear:(BOOL)animated {
    NSLog(@"%s", __FUNCTION__);

    if (![self.navigationController.viewControllers containsObject:self]) {
        // View has been popped! Important to distinguish between view popping and tab switching.
        // If parent view controller is active, pass a message.
        if (_refParentViewController && !_isSearchViewController) {
            _refParentViewController.valueX = @"xyz";
        }
    }

    [super viewWillDisappear:animated];
}

Now, there’s a case where following statement is executed (by Controller 1):

[self.navigationController popToRootViewControllerAnimated:NO];

As a result, i get a crash because _refParentViewController is a deallocated instance (at this point). How can i check whether _refParentViewController is valid? I thought that the view controllers/views will get destroyed in order but it appears that there isn’t any specific order and Controller 2 is destroyed before Controller 3.

I can check retainCount but i’m not sure if that’s a good idea.

Answer 1

I can check retainCount but i’m not
sure if that’s a good idea.

It is a horrible idea; retainCount is useless, don’t call it. And note that retainCount can never return 0; it can’t be used to know if an object is deallocated or not.

If both your parent and child properties are assign, then who is responsible for retaining the view controller? You need a retain that spans the expected lifespan of the parent/child properties.

I would suggest that you make the child property retain and leave the parent property as assign. You also need to make sure that when you set the child to nil (which, with a retain property will release it as long as you go through the property’s setter) that you first set the child’s parent property to nil.