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WWDC19

Table of Contents

=================

Advances in App Background Execution - Wednesday

Session materials: https://developer.apple.com/videos/play/wwdc2019/707/

Overview of Background Execution

Why Do We Enter Background State?

  • App requests
  • Specific event triggers. e.g: The user entering to a specific region or an updated health data

Important Considerations for Background Execution

  • Power
    • More execution = more battery drain
  • Performance
    • Smart CPU limits to minimize the impact to the user
  • Privacy

Background Execution Best Practices

Example: The messaging app

  • Sending messages: User expects immediate completion even if they leave the app before sending a message
    • Background task completion
      • Gives app additional time to run in the background before being suspended
      • Use expiration handlers if the event is still not completed within the time frame
  • Phone Calls
    • VoIP push notifications
      • Special type of push that launches your app
      • Must report incoming call with CallKit in the callback
      • Set apns-expiration on push to 0 or something small
      • Prefer a banner? Use standard pushes
  • Muted threads: The user may have many different threads and not want alerts for the specific thread
    • Use background pushes
      • Send push with content-available: 1 without badge or sound
      • must set apns-priority = 5 or the app will not launch
  • Download past attachments: User signs into the account and would like to get the older content once the app is backgrounded
    • Discretionary Background URL session
      • Allows the system to defer the download until a better time
      • Batching analytics to send later is also another good candidate for this

Deferrable Work

  • Syncing

  • Database cleanup

  • Backups

    • BackgroundTasks

      • A new framework for scheduling bg work

      • Available on all platforms

      • Several minutes of runtime at system-friendly times

        • e.g Maintenance work or Core ML training

    • Background App Refresh Task

      • A new API with the same policies
        • 30 secs of runtime

  • BGProcessingTask & BGAppRefreshTask

  • Old UIApplication fetch API is deprecated, and not supported on Mac

  • Adding capability under project settings (Signing & Capabilities)

  • requiresNetworkConnectivity: Bool & requiresExternalPower: Bool

  • Ability pause the debugger on simulator to simulate execution of tasks at a given time throughout the debugger!

Additional Considerations

  • Don't set earliestBeginDate too far into the future
  • Ensure files are accessible while the device is locked
    • FileProtectionType.completeUntilFirstUserAuthentication
  • UIScene apps should call UIApplication.requestSceneSessionRefresh(_:)
  • Consider calling BGTaskScheduler.submit() on a BG queue if submitting at launch