how do I use background fetch?

To use background fetch in your app, you can take advantage of the performFetchWithCompletionHandler method provided by the UIApplicationDelegate protocol. This method allows your app to fetch data in the background and update its content even when the app is not actively running.

Here are the steps to implement background fetch:

1. Enable Background Fetch:

   • Go to your app's target settings in Xcode.
   • Select the "Capabilities" tab.
   • Turn on "Background Modes" and check "Background fetch".

2. Implement performFetchWithCompletionHandler:

   • In your app delegate, implement the application(_:performFetchWithCompletionHandler:) method.
   • This method will be called by the system at appropriate times to allow your app to fetch new data.

func application(_ application: UIApplication, performFetchWithCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
    // Fetch your data here
    fetchData { newData in
        if newData {
            completionHandler(.newData)
        } else {
            completionHandler(.noData)
        }
    }
}

3. Schedule Background Fetch:
   • You can use setMinimumBackgroundFetchInterval to set how frequently your app should fetch data.

application.setMinimumBackgroundFetchInterval(UIApplication.backgroundFetchIntervalMinimum)

4. Fetch Data:
   • Implement your data fetching logic in a separate method and call it from performFetchWithCompletionHandler.

func fetchData(completion: @escaping (Bool) -> Void) {
    // Your data fetching logic here
    // Call completion(true) if new data is fetched, otherwise call completion(false)
}

For more detailed information on background fetch and other related topics, you might find the session Extend your app’s controls across the system useful, especially the chapter on "Update toggle states" which starts at 399 seconds. This session covers various aspects of updating app states and controls, which can be relevant when dealing with background fetch scenarios.