Where Did My State Go?

Transcript

1. Where Did My State Go?
   Subhrajyoti Sen
   @iamsubhrajyoti
   

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2. This is a Lifecycle talk
   

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3. The First thing
   

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4. The First thing
   We have all done this
   

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5. The First thing
   We have all done this
   android:name=".main.MainActivity"
   android:screenOrientation="portrait">
   

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6. Is this Enough?
   

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7. NO
   

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8. NO
   

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9. But WHY?
   

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10. Reasons
    

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11. Reasons
    1. Dark Theme
    

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12. Reasons
    1. Dark Theme
    2. Multi-Window
    

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

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14. Dark Theme
    

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15. Dark Theme
    Introduced in Android 10
    

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

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17. Dark Theme
    

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18. Dark Theme
    Triggers a uiMode configuration change
    

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

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20. Dark Theme
    android:name=".MyActivity"
    android:configChanges="uiMode" />
    

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21. Dark Theme
    android:name=".MyActivity"
    android:configChanges="uiMode" />
    This will invoke onConfigurationChanged() and not recreate all started Activities.
    

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22. Multi-Window
    

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23. Multi-Window
    

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24. Multi-Window
    

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25. Multi-Window
    Introduced in Android N
    

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

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

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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
    

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29. Multi-Window
    Portrait orientation != Vertical device
    

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

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31. Process Death
    

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

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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.
    

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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.
    

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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
    

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

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37. ViewModel
    

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

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

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40. ViewModel - SavedStateHandle
    

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

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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")?: ""
    }
    }
    

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

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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)
    }
    }
    

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45. 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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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
    }
    }
    

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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
    }
    }
    

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48. What about TESTING?
    

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49. Testing Activity/Fragment Recreation
    

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50. Testing Activity/Fragment Recreation
    Can be done with Espresso
    

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

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

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53. Testing Fragment Recreation
    

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

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

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

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

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58. Testing Fragment Lifecycle
    

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

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

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61. Thank You
    @iamsubhrajyoti
    

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