The final step in enabling background fetch for MustC is to add the application(_:performFetchWithCompletionHandler:) method to AppDelegate. As explained before, this method is called by iOS whenever the app is woken up in the background, and it allows you to perform an arbitrary amount of work. Once the app is done performing its task, it must call the completion-handler that was passed to this method.

Upon calling the completion-handler, you should inform iOS about the results of the operations you performed. It's important to correctly report this status because background fetch is intended to improve the user experience. If you falsely report to iOS that you have new data all the time, so your app is woken up more often, you're degrading the user experience. You should trust the system to judge when your app is woken up. It's in the best interest of your users, their battery life, and ultimately your app to not abuse background fetch.

To efficiently implement background fetch, you will work through the following steps:

1. Updating the data model so you can query the movie database more efficiently.
2. Refactoring the existing code to use the improved data model.
3. Implementing background fetch with the existing helper struct.

The first two steps are not directly tied to implementing background fetch, but they do illustrate that an efficient background fetch strategy may involve refactoring some of your app's existing code. Remember, there is nothing wrong with refactoring old code to implement a new feature. Both the new feature and the old code will usually benefit from refactoring.