Save the state

Transcript

1. Save the state
   Keishin Yokomaku (@KeithYokoma) / Giftmall, Inc.
   Shibuya.apk #42
   

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2. Save the state
   About me
   ▸ Keishin Yokomaku - @KeithYokoma
   
   
   ▸ Giftmall, Inc.
   
   
   ▸ Android App Engineer
   
   
   ▸ https://keithyokoma.dev/
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   Shibuya.apk #42
   

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3. Shibuya.apk #42
   Save the state
   

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4. Save the state
   References
   ▸ Best practices for saving UI state on Android
   

   https://youtu.be/V-s4z7B_Gnc
   
   
   ▸ Advanced state and side effects in Jetpack Compose
   

   https://youtu.be/TbxCz5AljQk
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5. Save the state
   Quick run-through: Activity lifecycle
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   source: https://developer.android.com/guide/components/activities/activity-lifecycle
   

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6. Save the state
   Quick run-through: Activity lifecycle
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   source: https://developer.android.com/guide/components/activities/activity-lifecycle
   

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7. Save the state
   Quick run-through: Activity lifecycle
   ▸ Rebirthing activities
   
   
   ▸ System creates a new activity instance
   
   
   ▸ When this happens
   
   
   ▸ On low memory
   
   
   ▸ Con
   fi
   guration changes
   
   
   ▸ Don’t keep activities
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   source: https://developer.android.com/guide/components/activities/activity-lifecycle
   

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8. Save the state
   Quick run-through: Activity lifecycle
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   source: https://gifer.com/en/2Dn8
   

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9. Save the state
   Quick run-through: Activity lifecycle
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   source: https://giphy.com/gifs/6qqnulwmAJozb51SCe
   

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10. Save the state
    Not saving state: views
    class SampleActivity : ComponentActivity(R.layout.activity_sample) {
    
    
    var count: Int = 0
    
    
    override fun onCreate(savedInstanceState: Bundle?) {
    
    
    super.onCreate(savedInstanceState)
    
    
    val counterText = findViewById(R.id.counter)
    
    
    updateCounterText(counterText)
    
    
    findViewById(R.id.counter_button).setOnClickListener {
    
    
    count++
    
    
    updateCounterText(counterText)
    
    
    }
    
    
    }
    
    
    private fun updateCounterText(counterText: TextView) {
    
    
    counterText.text = "Count: $count"
    
    
    }
    
    
    }
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11. Save the state
    Not saving state: views
    class SampleActivity : ComponentActivity(R.layout.activity_sample) {
    
    
    var count: Int = 0
    
    
    override fun onCreate(savedInstanceState: Bundle?) {
    
    
    super.onCreate(savedInstanceState)
    
    
    val counterText = findViewById(R.id.counter)
    
    
    updateCounterText(counterText)
    
    
    findViewById(R.id.counter_button).setOnClickListener {
    
    
    count++
    
    
    updateCounterText(counterText)
    
    
    }
    
    
    }
    
    
    private fun updateCounterText(counterText: TextView) {
    
    
    counterText.text = "Count: $count"
    
    
    }
    
    
    }
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    count is 0 when activity instance is created
    Shibuya.apk #42
    

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12. Save the state
    Not saving state: views
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13. Save the state
    Saving state: views
    class ViewActivity : ComponentActivity(R.layout.activity_view) {
    
    
    var count: Int = 0
    
    
    override fun onCreate(savedInstanceState: Bundle?) {
    
    
    super.onCreate(savedInstanceState)
    
    
    savedInstanceState?.getInt("count")?.let { count = it }
    
    
    // …
    
    
    }
    
    
    override fun onSaveInstanceState(outState: Bundle) {
    
    
    outState.putInt("count", count)
    
    
    super.onSaveInstanceState(outState)
    
    
    }
    
    
    }
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14. Save the state
    Saving state: views
    class ViewActivity : ComponentActivity(R.layout.activity_view) {
    
    
    var count: Int = 0
    
    
    override fun onCreate(savedInstanceState: Bundle?) {
    
    
    super.onCreate(savedInstanceState)
    
    
    savedInstanceState?.getInt("count")?.let { count = it }
    
    
    // …
    
    
    }
    
    
    override fun onSaveInstanceState(outState: Bundle) {
    
    
    outState.putInt("count", count)
    
    
    super.onSaveInstanceState(outState)
    
    
    }
    
    
    }
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    Save the value for the new instance
    Shibuya.apk #42
    

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15. Save the state
    Saving state: views
    class ViewActivity : ComponentActivity(R.layout.activity_view) {
    
    
    var count: Int = 0
    
    
    override fun onCreate(savedInstanceState: Bundle?) {
    
    
    super.onCreate(savedInstanceState)
    
    
    savedInstanceState?.getInt("count")?.let { count = it }
    
    
    // …
    
    
    }
    
    
    override fun onSaveInstanceState(outState: Bundle) {
    
    
    outState.putInt("count", count)
    
    
    super.onSaveInstanceState(outState)
    
    
    }
    
    
    }
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    Restore the saved value if present
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16. Save the state
    Saving state: views
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17. Save the state
    Not saving state: compose
    @Composable
    
    
    fun SampleScreen() {
    
    
    var count: Int by remember { mutableStateOf(0) }
    
    
    Column {
    
    
    Text(text = "Count: $count")
    
    
    Button(onClick = { count++ }) {
    
    
    Text(text = "Increase")
    
    
    }
    
    
    }
    
    
    }
    
    
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18. Save the state
    Not saving state: compose
    @Composable
    
    
    fun SampleScreen() {
    
    
    var count: Int by remember { mutableStateOf(0) }
    
    
    Column {
    
    
    Text(text = "Count: $count")
    
    
    Button(onClick = { count++ }) {
    
    
    Text(text = "Increase")
    
    
    }
    
    
    }
    
    
    }
    
    
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    count is not saved and restored at activity destruction
    

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19. Save the state
    Saving state: compose
    @Composable
    
    
    fun SampleScreen() {
    
    
    var count: Int by rememberSaveable { mutableStateOf(0) }
    
    
    Column {
    
    
    Text(text = "Count: $count")
    
    
    Button(onClick = { count++ }) {
    
    
    Text(text = "Increase")
    
    
    }
    
    
    }
    
    
    }
    
    
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20. Save the state
    Saving state: compose
    @Composable
    
    
    fun SampleScreen() {
    
    
    var count: Int by rememberSaveable { mutableStateOf(0) }
    
    
    Column {
    
    
    Text(text = "Count: $count")
    
    
    Button(onClick = { count++ }) {
    
    
    Text(text = "Increase")
    
    
    }
    
    
    }
    
    
    }
    
    
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    count is saved and restored
    

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21. Save the state
    remember vs rememberSaveable
    ▸ remember
    
    
    ▸ Remember any type of the value
    
    
    ▸ rememberSaveable
    
    
    ▸ Remember Bundle-supported type of the value
    
    
    ▸ Add more support with Parcelable framework or Saver interface
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22. Save the state
    Save custom data objects
    // views
    
    
    class ViewActivity : ComponentActivity(R.layout.activity_view) {
    
    
    var count: MyValueObject = MyValueObject(0)
    
    
    override fun onSaveInstanceState(outState: Bundle) {
    
    
    outState.putParcelable("count", count)
    
    
    super.onSaveInstanceState(outState)
    
    
    }
    
    
    }
    
    
    // composables
    
    
    @Composable
    
    
    fun SampleScreen() {
    
    
    var count: MyValueObject by rememberSaveable {
    
    
    mutableStateOf(MyValueObject(0))
    
    
    }
    
    
    }
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23. Save the state
    Save custom data objects
    // views
    
    
    class ViewActivity : ComponentActivity(R.layout.activity_view) {
    
    
    var count: MyValueObject = MyValueObject(0)
    
    
    override fun onSaveInstanceState(outState: Bundle) {
    
    
    outState.putParcelable("count", count)
    
    
    super.onSaveInstanceState(outState)
    
    
    }
    
    
    }
    
    
    // composables
    
    
    @Composable
    
    
    fun SampleScreen() {
    
    
    var count: MyValueObject by rememberSaveable {
    
    
    mutableStateOf(MyValueObject(0))
    
    
    }
    
    
    }
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    MyValueObject should be Parcelable!
    
    
    Compilation error 💥
    Requires Saver for MyValueObject or
    
    
    MyValueObject should be Parcelable!
    
    
    Runtime error 💥
    

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24. Save the state
    Save custom data objects: Parcelables
    // apply Parcelize plugin in build.gradle
    
    
    @Parcelize
    
    
    data class MyValueObject(
    
    
    val count: Int,
    
    
    ) : Parcelable
    
    
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25. Save the state
    Save custom data objects: Savers
    @Composable
    
    
    fun SampleScreen() {
    
    
    var count: MyValueObject by rememberSaveable(stateSaver = MyValueObjectSaver) {
    
    
    mutableStateOf(MyValueObject(0))
    
    
    }
    
    
    // …
    
    
    }
    
    
    val MyValueObjectSaver = Saver(
    
    
    save = { obj ->
    
    
    obj.count
    
    
    },
    
    
    restore = { count ->
    
    
    MyValueObject(count = count)
    
    
    },
    
    
    )
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    Shibuya.apk #42
    

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26. Save the state
    Save custom data objects: Savers
    @Composable
    
    
    fun SampleScreen() {
    
    
    var count: MyValueObject by rememberSaveable(stateSaver = MyValueObjectSaver) {
    
    
    mutableStateOf(MyValueObject(0))
    
    
    }
    
    
    // …
    
    
    }
    
    
    val MyValueObjectSaver = Saver(
    
    
    save = { obj ->
    
    
    obj.count
    
    
    },
    
    
    restore = { count ->
    
    
    MyValueObject(count = count)
    
    
    },
    
    
    )
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    Convert type into Bundle-supported one on save
    

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27. Save the state
    Save custom data objects: Savers
    @Composable
    
    
    fun SampleScreen() {
    
    
    var count: MyValueObject by rememberSaveable(stateSaver = MyValueObjectSaver) {
    
    
    mutableStateOf(MyValueObject(0))
    
    
    }
    
    
    // …
    
    
    }
    
    
    val MyValueObjectSaver = Saver(
    
    
    save = { obj ->
    
    
    obj.count
    
    
    },
    
    
    restore = { count ->
    
    
    MyValueObject(count = count)
    
    
    },
    
    
    )
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    Shibuya.apk #42
    Convert saved value to
    

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28. Save the state
    Save custom data objects: Savers
    @Composable
    
    
    fun SampleScreen() {
    
    
    var count: MyValueObject by rememberSaveable(stateSaver = MyValueObjectSaver) {
    
    
    mutableStateOf(MyValueObject(0))
    
    
    }
    
    
    // …
    
    
    }
    
    
    val MyValueObjectSaver = Saver(
    
    
    save = { obj ->
    
    
    obj.count
    
    
    },
    
    
    restore = { count ->
    
    
    MyValueObject(count = count)
    
    
    },
    
    
    )
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    Use stateSaver to save/restore
    

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29. Save the state
    ViewModel as a StateHolder
    class MyViewModel(
    
    
    private val countRepository: CountRepository,
    
    
    ) : ViewModel() {
    
    
    private val countMutation = MutableStateFlow(0)
    
    
    val count: StateFlow = countMutation.asStateFlow()
    
    
    }
    
    
    class MyFragment : Fragment() {
    
    
    private val viewModel: MyViewModel by viewModels()
    
    
    }
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30. Save the state
    ViewModel as a StateHolder
    class MyViewModel(
    
    
    private val countRepository: CountRepository,
    
    
    ) : ViewModel() {
    
    
    private val countMutation = MutableStateFlow(0)
    
    
    val count: StateFlow = countMutation.asStateFlow()
    
    
    }
    
    
    class MyFragment : Fragment() {
    
    
    private val viewModel: MyViewModel by viewModels()
    
    
    }
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    ViewModel instance is kept during con
    fi
    guration changes
    

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31. Save the state
    ViewModel as a StateHolder
    class MyViewModel(
    
    
    private val countRepository: CountRepository,
    
    
    ) : ViewModel() {
    
    
    private val countMutation = MutableStateFlow(0)
    
    
    val count: StateFlow = countMutation.asStateFlow()
    
    
    }
    
    
    class MyFragment : Fragment() {
    
    
    private val viewModel: MyViewModel by viewModels()
    
    
    }
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    Shibuya.apk #42
    ViewModel instance is lost when Activity is destroyed for low memory…
    

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32. Save the state
    ViewModel + SavedState Handle
    class MyViewModel(
    
    
    private val countRepository: CountRepository,
    
    
    private val savedStateHandle: SavedStateHandle,
    
    
    ) : ViewModel() {
    
    
    private val countMutation = MutableStateFlow(
    
    
    savedStateHandle["count"] ?: 0
    
    
    )
    
    
    val count: StateFlow = countMutation.asStateFlow()
    
    
    fun saveState() { savedStateHandle["count"] = countMutation.value }
    
    
    }
    
    
    class MyFragment : Fragment() {
    
    
    private val viewModel: MyViewModel by viewModels()
    
    
    override fun onSaveInstanceState(outState: Bundle) {
    
    
    viewModel.saveState()
    
    
    }
    
    
    }
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33. Save the state
    ViewModel + SavedState Handle
    class MyViewModel(
    
    
    private val countRepository: CountRepository,
    
    
    private val savedStateHandle: SavedStateHandle,
    
    
    ) : ViewModel() {
    
    
    private val countMutation = MutableStateFlow(
    
    
    savedStateHandle["count"] ?: 0
    
    
    )
    
    
    val count: StateFlow = countMutation.asStateFlow()
    
    
    fun saveState() { savedStateHandle["count"] = countMutation.value }
    
    
    }
    
    
    class MyFragment : Fragment() {
    
    
    private val viewModel: MyViewModel by viewModels()
    
    
    override fun onSaveInstanceState(outState: Bundle) {
    
    
    viewModel.saveState()
    
    
    }
    
    
    }
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    Use SavedStateHandle to save and restore values
    

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34. Save the state
    Save custom data objects: Savers for reusable UI element states
    class MyValueState(
    
    
    private val countRepository: CountRepository,
    
    
    initial: Int,
    
    
    ) {
    
    
    var count: MutableState = mutableStateOf(initial)
    
    
    private set
    
    
    }
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35. Save the state
    Save custom data objects: Savers for reusable UI element states
    @Composable
    
    
    fun rememberMyValueState(
    
    
    countRepository: CountRepository,
    
    
    initialCount: Int,
    
    
    ) {
    
    
    return rememberSaveable(
    
    
    inputs = arrayOf(countRepository, initialCount),
    
    
    saver = MyValueState.saver(countRepository),
    
    
    ) {
    
    
    MyValueState(countRepository, initialCount)
    
    
    }
    
    
    }
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36. Save the state
    Save custom data objects: Savers for reusable UI element states
    class MyValueState(
    
    
    private val countRepository: CountRepository,
    
    
    initial: Int,
    
    
    ) {
    
    
    companion object {
    
    
    fun saver(
    
    
    repository: CountRepository,
    
    
    ): Saver = Saver(
    
    
    save = { state -> state.count },
    
    
    restore = { value -> MyValueState(repository, value) },
    
    
    )
    
    
    }
    
    
    }
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37. Save the state
    Save custom data objects: Savers for reusable view element states
    class MyValueState(
    
    
    private val countRepository: CountRepository,
    
    
    initial: Int,
    
    
    ) {
    
    
    var count: Int = initial
    
    
    }
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38. Save the state
    Save custom data objects: Savers for reusable view element states
    class MyValueState(
    
    
    private val countRepository: CountRepository,
    
    
    initial: Int,
    
    
    ) : SavedStateRegistry.SavedStateProvider {
    
    
    var count: Int = initial
    
    
    override fun saveState(): Bundle = bundleOf(
    
    
    "count" to count
    
    
    )
    
    
    }
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39. Save the state
    Save custom data objects: Savers for reusable view element states
    class MyValueState(
    
    
    private val countRepository: CountRepository,
    
    
    initial: Int,
    
    
    registryOwner: SavedStateRegistryOwner,
    
    
    ) : SavedStateRegistry.SavedStateProvider {
    
    
    var count: Int = initial
    
    
    init {
    
    
    registryOwner.lifecycle.addObserver(
    
    
    LifecycleEventObserver { _, event ->
    
    
    // TODO: recover the state from saved state registry
    
    
    }
    
    
    )
    
    
    }
    
    
    }
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40. Save the state
    Save custom data objects: Savers for reusable view element states
    LifecycleEventObserver { _, event ->
    
    
    if (event == Lifecycle.Event.ON_CREATE) {
    
    
    val reg = registryOwner.savedStateRegistry
    
    
    if (reg.getSavedStateProvider("provider") == null) {
    
    
    reg.registerSavedStateProvider("provider", this)
    
    
    }
    
    
    val state = reg.consumeRestoredStateForKey("provider")
    
    
    count = state?.getInt("count") ?: initial
    
    
    }
    
    
    }
    
    
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41. Save the state
    Save custom data objects: Savers for reusable view element states
    class MyValueState(
    
    
    private val countRepository: CountRepository,
    
    
    initial: Int,
    
    
    registryOwner: SavedStateRegistryOwner,
    
    
    ) : SavedStateRegistry.SavedStateProvider
    
    
    class MyFragment : Fragment() {
    
    
    private var state: MyValueState = MyValueState(
    
    
    countRepository = // …
    
    
    initial = 0,
    
    
    registryOwner = this,
    
    
    )
    
    
    }
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42. Save the state
    Save custom data objects: Savers for reusable view element states
    class MyValueState(
    
    
    private val countRepository: CountRepository,
    
    
    initial: Int,
    
    
    registryOwner: SavedStateRegistryOwner,
    
    
    ) : SavedStateRegistry.SavedStateProvider
    
    
    class MyFragment : Fragment() {
    
    
    private var state: MyValueState = MyValueState(
    
    
    countRepository = // …
    
    
    initial = 0,
    
    
    registryOwner = this,
    
    
    )
    
    
    }
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43. Save the state
    Advanced use case
    ▸ Control rememberSaveable value’s lifecycle
    
    
    ▸ Saveable values are disposed on exit composition by default
    
    
    ▸ We can extend the lifecycle
    
    
    ▸ as long as the navigation destination is in the back stack
    
    
    ▸ similar to navGraphViewModels
    
    
    ▸ see: https://youtu.be/V-s4z7B_Gnc?t=874
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44. Save the state
    Stop stopping
    ▸ Con
    fi
    guration changes
    
    
    ▸ Fixing screen orientation doesn’t help
    
    
    ▸ Can’t stop device folding, theme / locale changes, etc…
    
    
    ▸ Stopping con
    fi
    g changes
    
    
    ▸ It’s on you, not the system; More code required to handle this
    
    
    ▸ Can’t stop activity recreation for some con
    fi
    guration changes
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    ? android:configChanges="orientation"
    

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45. Save the state
    Stop stopping
    ▸ Don’t keep activities
    
    
    ▸ Developer option to always dispose activity instance
    
    
    ▸ Activity disposal can happen without enabling this option
    
    
    ▸ ViewModel will lost its data without SavedStateHandle
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46. Save the state
    Caveats 1: SavedStateHandle limitations
    ▸ no more than 1MB data size in 1 process
    
    
    ▸ Same as Bundle!
    
    
    ▸ otherwise TransactionTooLargeException 💥
    
    
    ▸ Avoid saving HUGE objects
    
    
    ▸ Bitmap obviously :)
    
    
    ▸ List containing lots of elements
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47. Save the state
    Caveats 1: SavedStateHandle limitations
    ▸ How to make value object properties transient
    
    
    ▸ Kotlin Parcelize: @IgnoredOnParcel
    
    
    ▸ Make sure to set the data after recreation!
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48. Save the state
    // Kotlin 1.6.20+
    
    
    @Parcelize
    
    
    data class SampleValue(
    
    
    val name: String = "",
    
    
    @IgnoredOnParcel val list: List = emptyList(),
    
    
    ) : Parcelable
    
    
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    Caveats 1: SavedStateHandle limitations
    

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49. Save the state
    Caveats 2: WebView
    ▸ Keeps reloading the webpage on showing the WebView
    
    
    ▸ form values are gone after recreation
    
    
    ▸ Accompanist WebView can save scroll position (0.31.1-alpha)
    
    
    ▸ What if we need to implement a image
    fi
    le chooser for …?
    
    
    ▸ Android 11+: no worries with stock Photo Picker, it’s transparent activity!
    
    
    ▸ Android 10 and below: no clue…
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50. Save the state
    Enable automatic installation of the backported photo picker
    
    
    
    
    
    android:name="com.google.android.gms.metadata.ModuleDependencies"
    
    
    android:enabled="false"
    
    
    android:exported="false"
    
    
    tools:ignore="MissingClass"
    
    
    >
    
    
    
    
    
    
    
    
    
    
    
    
    
    android:name="photopicker_activity:0:required"
    
    
    android:value=""
    
    
    />
    
    
    
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51. Save the state
    Keishin Yokomaku (@KeithYokoma) / Giftmall, Inc.
    Shibuya.apk #42
    

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