WWDC19

Table of Contents

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

• Advances in App Background Execution - Wednesday
  • Overview of Background Execution
    • Why Do We Enter Background State?
  • Important Considerations for Background Execution
  • Background Execution Best Practices
    • Example: The messaging app
  • Deferrable Work
    • BackgroundTasks
    • Background App Refresh Task
  • Additional Considerations

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