how can I use UIApplication.shared.beginBackgroundTask from an isolated actor?

To use UIApplication.shared.beginBackgroundTask from an isolated actor, you can leverage the @MainActor annotation to ensure that the code runs on the main actor. This is important because UIApplication.shared is isolated to the main actor, and accessing it from a different actor would require asynchronous context switching.

Here's a step-by-step approach based on the information from the WWDC session "Migrate your app to Swift 6":

1. Annotate the Function with @MainActor: This ensures that the function runs on the main actor, which is necessary for accessing UIApplication.shared.

2. Use @MainActor in Protocols: If the function is part of a protocol, you can annotate the protocol to guarantee that all its methods are called on the main actor.

3. Use assume isolated: If you are certain that the function will always be called on the main actor, you can use assume isolated to inform the compiler about this guarantee.

Here is an example implementation:

@MainActor
func startBackgroundTask() {
    let taskID = UIApplication.shared.beginBackgroundTask {
        // Cleanup code if the task expires
    }
    // Perform your background task here
    UIApplication.shared.endBackgroundTask(taskID)
}

If you are working within a protocol, you can annotate the protocol and its methods:

@MainActor
protocol BackgroundTaskHandler {
    func startBackgroundTask()
}

class MyBackgroundTaskHandler: BackgroundTaskHandler {
    func startBackgroundTask() {
        let taskID = UIApplication.shared.beginBackgroundTask {
            // Cleanup code if the task expires
        }
        // Perform your background task here
        UIApplication.shared.endBackgroundTask(taskID)
    }
}

For more details on using @MainActor and assume isolated, you can refer to the session Migrate your app to Swift 6 (24:15).

Relevant Sessions

• Migrate your app to Swift 6
• A Swift Tour: Explore Swift’s features and design