Where Did My State Go? - Speaker Deck

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Where Did My State Go? Subhrajyoti Sen @iamsubhrajyoti

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This is a Lifecycle talk

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The First thing

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The First thing We have all done this

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The First thing We have all done this

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Is this Enough?

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But WHY?

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Reasons

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Reasons 1. Dark Theme

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Reasons 1. Dark Theme 2. Multi-Window

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Reasons 1. Dark Theme 2. Multi-Window 3. Process Death

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Dark Theme

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Dark Theme Introduced in Android 10

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Dark Theme Introduced in Android 10 Can be changed by 1. System Toggle 2. AppCompat in-app

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Dark Theme

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Dark Theme Triggers a uiMode conﬁguration change

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Dark Theme Triggers a uiMode conﬁguration change All started Activities are automatically recreated.

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Dark Theme

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Dark Theme This will invoke onConﬁgurationChanged() and not recreate all started Activities.

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Multi-Window

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Multi-Window

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Multi-Window

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Multi-Window Introduced in Android N

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Multi-Window Introduced in Android N A slight change in Lifecycle.

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Multi-Window Introduced in Android N A slight change in Lifecycle. You can’t completely depend on onPause() and onResume()

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Multi-Window Introduced in Android N A slight change in Lifecycle. You can’t completely depend on onPause() and onResume() screenOrientation will be ignored

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Multi-Window Portrait orientation != Vertical device

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Multi-Window Portrait orientation != Vertical device android:resizeableActivity="false" to opt out of Multi-Window

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Process Death

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Process Death ● The device is running low on memory and the OS kills your app to free up memory.

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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.

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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.

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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

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Process Death - Testing 1. Put the app in background 2. adb shell am kill packagename

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ViewModel

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ViewModel ViewModels persist state across Activity recreation. ViewModels do not persist state on process death.

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ViewModel ViewModels persist state across Activity recreation. ViewModels do not persist state on process death. Use SavedStateHandle to save state.

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ViewModel - SavedStateHandle

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ViewModel - SavedStateHandle val viewModel = ViewModelProvider(this, SavedStateVMFactory(this)) .get(MyViewModel::class.java)

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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")?: "" } }

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Custom View Views can save their own state. Views need to have an ID to be able to save state.

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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) } }

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Custom View private class SavedState : BaseSavedState { //.. companion object { val CREATOR: Parcelable.Creator = object : Parcelable.Creator { override fun createFromParcel(source: Parcel) = SavedState(source) override fun newArray(size: Int) = arrayOfNulls(size) } } }

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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 } }

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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 } }

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What about TESTING?

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Testing Activity/Fragment Recreation

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Testing Activity/Fragment Recreation Can be done with Espresso

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Testing Activity/Fragment Recreation Can be done with Espresso Easier with AndroidX Test

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Testing Activity/Fragment Recreation Can be done with Espresso Easier with AndroidX Test debugImplementation 'androidx.fragment:fragment-testing:$fragment_version'

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Testing Fragment Recreation

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Testing Fragment Recreation @RunWith(AndroidJUnit4::class) class MyTestSuite { @Test fun testRecreation() { val scenario = launchFragmentInContainer() } }

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Testing Fragment Recreation @RunWith(AndroidJUnit4::class) class MyTestSuite { @Test fun testRecreation() { val scenario = launchFragmentInContainer() // perform actions } }

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Testing Fragment Recreation @RunWith(AndroidJUnit4::class) class MyTestSuite { @Test fun testRecreation() { val scenario = launchFragmentInContainer() // perform actions scenario.recreate() } }

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Testing Fragment Recreation @RunWith(AndroidJUnit4::class) class MyTestSuite { @Test fun testRecreation() { val scenario = launchFragmentInContainer() // perform actions scenario.recreate() // test events } }

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Testing Fragment Lifecycle

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Testing Fragment Lifecycle @RunWith(AndroidJUnit4::class) class MyTestSuite { @Test fun testLifecycle() { val scenario = launchFragmentInContainer() } }

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Testing Fragment Lifecycle @RunWith(AndroidJUnit4::class) class MyTestSuite { @Test fun testLifecycle() { val scenario = launchFragmentInContainer() scenario.moveToState(State.CREATED) } }

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Thank You @iamsubhrajyoti