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Question

I'd like to save some data to NSUserDefaults on the user leaving a table view in a UINavigation stack. I'd like to be able to still utilize the default back button (the button with the chevron), while still having a reliable way to save the data. I've tried using the viewDidDisappear method, but I'm not sure how reliable this is. I'm worried that it might be called when the app is killed (or any other system action that might call the method). The only way to exit the view controller is via the back button. I'm not sure what else to try, if what I have tried is a technique that can be used, please do tell. Thanks.

Answer 1

Maybe using the UINavigationControllerDelegate will help you in this, so you will be aware of popping and pushing in your navigation controller.

self.navigationController.delegate = self;

and in push or pop this delegate function will be called, you can check the view controller that will be presented.

- (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated
{
      if (viewController.class == [YourPreviousViewController class]) {
           //back clicked, poping
       }
}

Answer 2

We came across the same issue and ended up using a custom nav bar button with an action. It was fairly easy to mimic the default back arrow too. The reason we decided to go this way instead is because we found we didn't have enough control over the saving of data otherwise, it was possible that the data might not save in time before the view was dismissed. Also, in our case, the user may not have wanted to save the changes and just wanted to back out of the view. Using an action allowed us to present an alert to the user that the data was not saved and gave them the option to save or not.