Frustration-free orientation changes

Many apps do unexpected things when a user rotates the device. A message that has been painfully composed using the on-screen keyboard is just gone. Dialogs are disappearing. Data that took a while to load and display is gone and now the app is making the user wait again.

All of this is very frustrating to users. But if you know that an Activity is destroyed and then recreated on orientation change, this is not too surprising to you. Still, many beginners don’t know what is going on behind the scenes and consequently come up with flawed or incomplete ways to deal with the lifetime of an Activity.

If you have ever “fixed” a bug by changing your app’s manifest to manually handle orientation changes or by locking the device orientation, this talk is for you. It aims to give attendees a better understanding of the Activity lifetime/lifecycle. And we will look at the fundamental ways to deal with this situation. So you can write better apps.

Transcript

1. Frustration-free orientation changes cketti Twitter: @cketti
2. Frustration?
3. Frustration?
4. Frustration!
5. Frustration!
6. Frustration!
7. Frustration-free
8. What happens during an orientation change? destroyed recreated User-perceived Activity lifetime Activity instance lifetime
9. Dealing with Activity restarts
10. Handle the orientation change yourself AndroidManifest.xml: <activity android:name=".SearchActivity" android:configChanges="orientation|screenSize" … />
11. Handle the orientation change yourself SearchActivity.kt: override fun onConfigurationChanged(newConfig: Configuration) { super.onConfigurationChanged(newConfig) if (newConfig.orientation == Configuration.ORIENTATION_LANDSCAPE) { portraitOnlyView.setVisibility(View.GONE) } else { portraitOnlyView.setVisibility(View.VISIBLE) } }
12. Types of configuration changes • locale • density • fontScale • keyboard • keyboardHidden • layoutDirection • mcc • mnc • navigation • screenLayout • smallestScreenSize • touchscreen • uiMode • orientation • screenSize
13. Retain an object during a configuration change • Activity.onRetainNonConfigurationInstance() + getLastNonConfigurationInstance() • FragmentActivity.onRetainCustomNonConfigurationInstance() + getLastCustomNonConfigurationInstance() • Loaders • Fragment.setRetainInstance(true) • Android Architecture Components: ViewModel
14. Are we done?
15. No.
16. Android Low Memory Killer Image source: https://www.vecteezy.com/vector-art/66465-grim-reaper-tattoo
17. Saving state
18. onSaveInstanceState() override fun onSaveInstanceState(outState: Bundle) { super.onSaveInstanceState(outState) outState.putBoolean("optionalViewVisible", optionalView.isVisible) }
19. Limitations “A Bundle object isn't appropriate for preserving more than a trivial amount of data because it consumes system-process memory” – The Activity Lifecycle | Android Developers
20. onRestoreInstanceState() override fun onRestoreInstanceState(savedInstanceState: Bundle) { super.onRestoreInstanceState(savedInstanceState) optionalView.isVisible = savedInstanceState.getBoolean("optionalViewVisible") }
21. Restoring state in onCreate() override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) … if (savedInstanceState != null) { … } }
22. What state is saved for you? • Activity stack • Fragment stack • Platform UI widgets save user-modifiable UI state ◦ Views need to have an ID set
23. What state should you save? • As little as possible, as much as necessary • User input • Reference to original data source ◦ Database ID ◦ URL ◦ File name
24. Consequences
25. Timing java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState at android.support.v4.app.FragmentManagerImpl.checkStateLoss(FragmentManager.java:2053) at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:2079) at android.support.v4.app.BackStackRecord.commitInternal(BackStackRecord.java:678) at android.support.v4.app.BackStackRecord.commit(BackStackRecord.java:632) …
26. Timing state saved recreated Activity instance 1 Activity instance 2 Background operation UI update
27. Object references Don’t hold on to any object that references your Activity instance • Views • Inner classes in Activity
28. Being restored while waiting for user input EditUserActivity ImagePickerActivity Load User object startActivityForResult() onActivityResult() Update User object
29. Being restored while waiting for user input EditUserActivity ImagePickerActivity startActivityForResult() onActivityResult() Load User object Update User object Load User object
30. Testing
31. Manual testing • Rotate the device • Change language
32. Manual testing • Rotate the device • Change language • Change font size
33. Manual testing • Rotate the device • Change language • Change font size • Change display size
34. Manual testing • Rotate the device • Change language • Change font size • Change display size • Developer options ◦ Don’t keep activities
35. Manual testing • Rotate the device • Change language • Change font size • Change display size • Developer options ◦ Don’t keep activities ◦ Background process limit
36. Summary • Always save state • Retain an object as optimization • Don’t update the UI when you’re not supposed to • Check out ViewModel + LiveData
37. Thank you! cketti Twitter: @cketti Email: hello@cketti.de