What is the Xcode "Background Processing" Background Mode?

There is no documentation yet. But in WWDC2019, they explain what it is and how to use it. Here is the link: Apple WWDC 2019

Say like you wanted to clean up your database in background to delete old records. First, you have to enable background processing in your Background Modes Capabilities. Then in your Info.plist add the background task scheduler identifier:

Then in 'ApplicationDidFinishLaunchingWithOptions' method register your identifier with the task.

BGTaskScheduler.shared.register(forTaskWithIdentifier: "com.example.apple-samplecode.ColorFeed.db_cleaning", using: nil) { task in
    // Downcast the parameter to a processing task as this identifier is used for a processing request
    self.handleDatabaseCleaning(task: task as! BGProcessingTask)
}

Do the work that you wanted to perform in the background and put it into the operation queue. In our case, the cleanup function will looks like:

// Delete feed entries older than one day...
func handleDatabaseCleaning(task: BGProcessingTask) {
    let queue = OperationQueue()
    queue.maxConcurrentOperationCount = 1

    // Do work to setup the task
    let context = PersistentContainer.shared.newBackgroundContext()
    let predicate = NSPredicate(format: "timestamp < %@", NSDate(timeIntervalSinceNow: -24 * 60 * 60))
    let cleanDatabaseOperation = DeleteFeedEntriesOperation(context: context, predicate: predicate)

    task.expirationHandler = {
        // After all operations are canceled, the completion block is called to complete the task
        queue.cancelAllOperations()
    }

    cleanDatabaseOperation.completionBlock {
        // Perform the task
    }

    // Add the task to the queue
    queue.addOperation(cleanDatabaseOperation)
}

Now, when the app goes into the background we have to schedule the background task in BGTaskScheduler.

Note: BGTaskScheduler is a new feature to schedule multiple background tasks that will be performed into the background].

This background task will execute once a week to clean up my database. Check out the properties you can mention to define the task types.

"Background Processing" mode is required for running BGTaskScheduler tasks.

BGTaskScheduler:

A class for scheduling tasks run by submitting task requests that launch your app in the background. Configuring the App for Background Tasks Configure the app for background tasks by adding the capabilities for the required background modes, and by adding a whitelist of task identifiers.

Configuring the App for Background Tasks

Configure the app for background tasks by adding the capabilities for the required background modes, and by adding a whitelist of task identifiers.

Xcode Background Modes

App states

foreground -> background -> suspended -> terminated

background transfer - execute some task when app is in background mode

To add a capability to work in background mode

App Target -> Signing & Capabilities -> + Capability -> Background Modes

You can find a list of modes like:

• Audio - recording/playing audio in background mode
• Location - receive new location updates in background mode
• Background tasks
  • Background fetch - Background App Refresh Task - 30 seconds to fetch up-to-date data before loading app.
  • Background Processing Task - several minutes at system friendly times (e.g. right after app become background) to complete big task(clear video stuff) or priority task(send message)

[Background session]