iOS Programming: The Big Nerd Ranch Guide, 7th Edition

Background Tasks

You learned in Chapter 20 that blocking the main queue can lead to an unresponsive application, so it is often a good idea to do expensive operations using a background task. The viewContext of NSPersistentContainer is associated with the main queue, so long-running operations using the viewContext – like the insertion of photos from the web service – are good candidates for a background task.

You are going to update processPhotosRequest(data:error:) to use a background task. Background tasks are an asynchronous operation, so instead of returning a Result synchronously from your method, you will pass a completion handler to be called asynchronously.

Open PhotoStore.swift and update processPhotosRequest(data:error:) ...