Where Did My State Go?

Transcript

1. Where Did My State Go? Subhrajyoti Sen @iamsubhrajyoti
2. This is a Lifecycle talk
3. The First thing
4. The First thing We have all done this
5. The First thing We have all done this <activity android:name=".main.MainActivity" android:screenOrientation="portrait">
6. Is this Enough?
7. NO
8. NO
9. But WHY?
10. Reasons
11. Reasons 1. Dark Theme
12. Reasons 1. Dark Theme 2. Multi-Window
13. Reasons 1. Dark Theme 2. Multi-Window 3. Process Death
14. Dark Theme
15. Dark Theme Introduced in Android 10
16. Dark Theme Introduced in Android 10 Can be changed by 1. System Toggle 2. AppCompat in-app
17. Dark Theme
18. Dark Theme Triggers a uiMode configuration change
19. Dark Theme Triggers a uiMode configuration change All started Activities are automatically recreated.
20. Dark Theme <activity android:name=".MyActivity" android:configChanges="uiMode" />
21. Dark Theme <activity android:name=".MyActivity" android:configChanges="uiMode" /> This will invoke onConfigurationChanged() and not recreate all started Activities.
22. Multi-Window
23. Multi-Window
24. Multi-Window
25. Multi-Window Introduced in Android N
26. Multi-Window Introduced in Android N A slight change in Lifecycle.
27. Multi-Window Introduced in Android N A slight change in Lifecycle. You can’t completely depend on onPause() and onResume()
28. Multi-Window Introduced in Android N A slight change in Lifecycle. You can’t completely depend on onPause() and onResume() screenOrientation will be ignored
29. Multi-Window Portrait orientation != Vertical device
30. Multi-Window Portrait orientation != Vertical device android:resizeableActivity="false" to opt out of Multi-Window
31. Process Death
32. Process Death • The device is running low on memory and the OS kills your app to free up memory.
33. Process Death • The device is running low on memory and the OS kills your app to free up memory. • It happens if your app is in the Paused/Stopped state.
34. Process Death • The device is running low on memory and the OS kills your app to free up memory. • It happens if your app is in the Paused/Stopped state. • Cannot work around it.
35. Process Death - Testing 1. Developer Options -> Apps -> Background process limit 2. Choose ‘No background processes’ 3. Open your app and put in the background 4. Open another app and switch to your app
36. Process Death - Testing 1. Put the app in background 2. adb shell am kill packagename
37. ViewModel
38. ViewModel ViewModels persist state across Activity recreation. ViewModels do not persist state on process death.
39. ViewModel ViewModels persist state across Activity recreation. ViewModels do not persist state on process death. Use SavedStateHandle to save state.
40. ViewModel - SavedStateHandle
41. ViewModel - SavedStateHandle val viewModel = ViewModelProvider(this, SavedStateVMFactory(this)) .get(MyViewModel::class.java)
42. ViewModel - SavedStateHandle val viewModel = ViewModelProvider(this, SavedStateVMFactory(this)) .get(MyViewModel::class.java) class MyViewModel(val state : SavedStateHandle) : ViewModel() { fun saveProductId(productId: String) { state.set("productId", productId) } fun getProductId(): String { return state.get("productId")?: "" } }
43. Custom View Views can save their own state. Views need to have an ID to be able to save state.
44. Custom View private class SavedState : BaseSavedState { var value = 1 constructor(superState: Parcelable) : super(superState) private constructor(source: Parcel) : super(source) { value = source.readInt() } override fun writeToParcel(out: Parcel, flags: Int) { super.writeToParcel(out, flags) out.writeInt(value) } }
45. Custom View private class SavedState : BaseSavedState { //.. companion object { val CREATOR: Parcelable.Creator<SavedState> = object : Parcelable.Creator<SavedState> { override fun createFromParcel(source: Parcel) = SavedState(source) override fun newArray(size: Int) = arrayOfNulls<SavedState?>(size) } } }
46. Custom View class CustomView(context: Context) : View(context) { var value = 1 override fun onSaveInstanceState(): Parcelable { val superState = super.onSaveInstanceState() val state = SavedState(superState) state.value = this.value return state } }
47. Custom View class CustomView(context: Context) : View(context) { override fun onRestoreInstanceState(state: Parcelable) { val savedState = state as SavedState super.onRestoreInstanceState(savedState.superState) this.value = savedState.value } }
48. What about TESTING?
49. Testing Activity/Fragment Recreation
50. Testing Activity/Fragment Recreation Can be done with Espresso
51. Testing Activity/Fragment Recreation Can be done with Espresso Easier with AndroidX Test
52. Testing Activity/Fragment Recreation Can be done with Espresso Easier with AndroidX Test debugImplementation 'androidx.fragment:fragment-testing:$fragment_version'
53. Testing Fragment Recreation
54. Testing Fragment Recreation @RunWith(AndroidJUnit4::class) class MyTestSuite { @Test fun testRecreation() { val scenario = launchFragmentInContainer<MyFragment>() } }
55. Testing Fragment Recreation @RunWith(AndroidJUnit4::class) class MyTestSuite { @Test fun testRecreation() { val scenario = launchFragmentInContainer<MyFragment>() // perform actions } }
56. Testing Fragment Recreation @RunWith(AndroidJUnit4::class) class MyTestSuite { @Test fun testRecreation() { val scenario = launchFragmentInContainer<MyFragment>() // perform actions scenario.recreate() } }
57. Testing Fragment Recreation @RunWith(AndroidJUnit4::class) class MyTestSuite { @Test fun testRecreation() { val scenario = launchFragmentInContainer<MyFragment>() // perform actions scenario.recreate() // test events } }
58. Testing Fragment Lifecycle
59. Testing Fragment Lifecycle @RunWith(AndroidJUnit4::class) class MyTestSuite { @Test fun testLifecycle() { val scenario = launchFragmentInContainer<MyFragment>() } }
60. Testing Fragment Lifecycle @RunWith(AndroidJUnit4::class) class MyTestSuite { @Test fun testLifecycle() { val scenario = launchFragmentInContainer<MyFragment>() scenario.moveToState(State.CREATED) } }
61. Thank You @iamsubhrajyoti