The document discusses doing background tasks on iOS, which is limited to a few options. It can explain that apps can register to receive location updates, play audio, or perform VOIP tasks in the background by setting the appropriate value in the app's Info.plist file. The document provides code samples and demos for receiving location updates and playing audio in the background. Developers are warned that background tasks may drain the user's battery.

1. Backgrounding
Bursting Your Bubble on iOS

2. Sorry
Doing what you want in the background
is almost impossible

3. photo by protographer23

4. Get Your Notepads
Ready
Suspending vs. Resuming
Local Notifications
Doing Stuff in the Background

5. Exiting vs. Resume
Since iOS 4, you can keep your app
“open” on exit
But it’s really just a “freeze” and
resume - nothing happens while it’s
in the background

6. Resume Me
Set the ‘UIApplicationExitsOnSuspend’
to ‘NO’ in your Info.plist

7. App Delegate Events
App Initial Load -> Exit:
applicationDidBecomeActive
applicationWillResignActive
applicationDidEnterBackground
On Relaunch:
applicationWillEnterForeground

8. Sounds Promising
applicationDidEnterBackground sounds
promising, but you can’t do anything
inside it that is long-running.
Docs say you have 5 seconds
You can’t get back to the UI

9. Terminate on Exit
Set ‘UIApplicationExitsOnSuspend’ to
‘YES’ in your Info.plist

10. App Delegate Events
App Launch -> Exit:
applicationDidBecomeActive
applicationDidEnterBackground
applicationWillTerminate

11. Kill Me
If the user does the jiggle and Red-
Xes the app, no events are fired

12. DEMO!

13. Local Notifications
You can schedule local notifications
to prompt the user at a future time
even if your app isn’t running
Useful - but remember the user isn’t
required to open the app, and your
notification may never appear

14. DEMO!

15. Ok, Next
So you “can” do things in the
background, but it’s limited to 3
things:
Get GPS updates
Play Justin Bieber
Do the VOIP

16. Set Your Plist
Do do one of those 3 lovely things in
the background, set the
‘UIBackgroundModes’ in your
Info.plist
Values are: location, audio, voip

17. Location
Get super duper real-time updates or
major changes only
Use CLLocationManager to do the magic

18. DEMO!

19. Playing Audio
It’s easy: start playing your tunes
using AV* framework.
If something else starts playing
music, you lose

20. DEMO!

21. VOIP
Sorry, no demo.
But supposedly you can open a socket
and keep it open.

22. Fighting the Man
People have tried tricking the system
by playing an “empty” sound file.
This works until some other app plays
sound.
GPS Updates take up battery power, so
your users may hate you.

23. Conclusion
Read more at:
http://developer.apple.com/library/ios/
#documentation/iphone/conceptual/
iphoneosprogrammingguide/
BackgroundExecution/
BackgroundExecution.html
Sample Code: https://github.com/
dnstevenson/BackgroundTest
Good Luck!

24. Thanks!
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www.stevensonsoftware.com
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