@GDG Korea Android - Google I/O Extended Android

1. KimKevin
Android Developer / Kakaobank
Android Jetpack
ViewModel and Testing

4. ViewModel

5. Model
Presenter
View
Repository
The past of past

6. Model
ViewModel
(Not AAC)
Presenter
Repository
View
Databinding
The past

7. Model
AAC ViewModel
Repository
View
Databinding
The present

8. ViewModel
! The Lifecycle Library’s ViewModel class
! android.arch.lifecycle -> androidx.lifecycle
! Provides data for UI components and survive configuration changes.

9. ViewModel can help
! Avoiding memory leaks
! Solving common Android lifecycle challenges

10. ViewModel can help
! Avoiding memory leaks
! Solving common Android lifecycle challenges
! Share data between fragments

11. class UserViewModel : ViewModel() {
val name = MutableLiveData<String>()
}
class UserFragment : Fragment() {
override fun onCreate(savedInstanceState: Bundle?) {
val userViewModel =
ViewModelProviders.of(getActivity()).get(UserViewModel::class.java)
loginButton.setOnClickListener({ item -> userViewModel.name = item })
}
}
class UserProfileFragment : Fragment() {
override fun onCreate(savedInstanceState: Bundle?) {
val userViewModel =
ViewModelProviders.of(getActivity()).get(UserViewModel::class.java)
userViewModel.name.observe(this, { name ->
// Update the UI.
})
}
}

12. ViewModel can help
! Avoiding memory leaks
! Solving common Android lifecycle challenges
! Share data between fragments
! Design good software (SRP, testing etc)

13. Activity
Activity
Data Loading
Drawing UI
Components
Processing Data
Handling all UI
Interactions
Saving and
restoring the UI

14. Data Loading
Drawing UI
Components
Processing Data
Handling all UI
Interactions
Saving and
restoring the UI
Activity
Activity
https://stackify.com/solid-design-principles

15. Data Loading
Drawing UI
Components
Processing Data
Handling all UI
Interactions
Saving and
restoring the UI
Activity
Activity
Single Responsibility Principle
https://stackify.com/solid-design-principles

16. Activity
Drawing UI
Receiving User Interactions
as Android Developer

17. Activity
Drawing UI
Receiving User Interactions
ViewModel
Hold UI Data
Repository
API for saving and loading app data
Presenter
Process data for UI
User Case
full fledged clean architecture
And more…
as Android Developer
as Java Developer

18. Activity
Drawing UI
Receiving User Interactions
ViewModel
Hold UI Data
Repository
API for saving and loading app data
Presenter
Process data for UI
User Case
full fledged clean architecture
And more…
as Android Developer
as Java Developer
Provides
APIs
Testable
Code

19. Reactive UI
! ViewModel
! LiveData
! Data Binding
! Android Studio 3.1 +
! Support for ViewModel and LiveData
! setLifecycleOwner(LifecycleOwner)

20. ViewModel could do
! Handle configuration changes
! Replace onSaveInstanceState()

21. Activity Instance
Activity UI data

22. Activity Instance
RotationEvent
Activity UI data

23. Activity Instance
Recreated Activity
Instance
RotationEvent
Forgotten data that didn’t get passed to next activity
Activity UI data

24. <activity android:name="MainActivity"
android:configChanges="screenSize|orientation" />
Activity
Fragment
public void onCreate(@Nullable Bundle savedInstanceState) {
···
setRetainInstance(true)
}

25. ViewModel
Activity Instance
Activity UI data

26. ViewModel
Activity UI data
RotationEvent
Activity Instance

27. ViewModel
Activity UI data
Activity Instance
Recreated Activity
Instance
RotationEvent

28. class UserLoginViewModel : ViewModel() {
private val _id = MutableLiveData<String>()
val id: LiveData<String>
get() = _id
private val _password = MutableLiveData<String>()
val password: LiveData<String>
get() = _password
···
}

29. public abstract class ViewModel {
@SuppressWarnings("WeakerAccess")
protected void onCleared() { }
}

30. public abstract class ViewModel {
@SuppressWarnings("WeakerAccess")
protected void onCleared() { }
}
@Override
protected void onDestroy() {
super.onDestroy();
···
mViewModelStore.clear();
···
}
FragmentActivity & Fragment

31. public final void clear() {
for (ViewModel vm : mMap.values()) {
vm.onCleared();
}
mMap.clear();
}
@Override
protected void onDestroy() {
super.onDestroy();
···
mViewModelStore.clear();
···
}
FragmentActivity & Fragment
ViewModelStore

32. WARNING!
! Don’t store Contexts in a ViewModel
! Activities, Fragments, Views, etc

33. ViewModel
Activity UI data
Activity Instance
If you store an
Activity

34. ViewModel
Activity UI data
Activity Instance
If you store an
Activity
RotationEvent

35. ViewModel
Activity UI data
Activity Instance
If you store an
Activity
RotationEvent
Recreated Activity
Instance
MEMORY LEAK

37. override fun onCreate(savedInstanceState: Bundle?) {
···
val userLoginViewModel =
ViewModelProviders.of(this, factory).get(UserLoginViewModel::class.java)
}
ViewModelProdivers.of() creates a ViewModelProvider

38. public static ViewModelProvider of(@NonNull FragmentActivity activity,
@Nullable Factory factory) {
Application application = checkApplication(activity);
if (factory == null) {
factory = ViewModelProvider.AndroidViewModelFactory.getInstance(application);
}
return new ViewModelProvider(activity.getViewModelStore(), factory);
}
override fun onCreate(savedInstanceState: Bundle?) {
···
val userLoginViewModel =
ViewModelProviders.of(this, factory).get(UserLoginViewModel::class.java)
}
ViewModelProviders

39. public static ViewModelProvider of(@NonNull FragmentActivity activity,
@Nullable Factory factory) {
// Lifecycles 2.0.0-alpha1 (AndroidX)
return new ViewModelProvider(activity.getViewModelStore(), factory);
// Lifecycles 1.1.1
return new ViewModelProvider(ViewModelStores.of(activity), factory);
}
ViewModelProviders

40. public static ViewModelStore of(@NonNull FragmentActivity activity) {
if (activity instanceof ViewModelStoreOwner) {
return ((ViewModelStoreOwner) activity).getViewModelStore();
}
return holderFragmentFor(activity).getViewModelStore();
}
public HolderFragment() {
setRetainInstance(true);
}
public static ViewModelProvider of(@NonNull FragmentActivity activity,
@Nullable Factory factory) {
···
return new ViewModelProvider(ViewModelStores.of(activity), factory);
}
ViewModelStores (Not included in AndroidX)
ViewModelProviders
Lifecycles 1.1.1

41. public static ViewModelProvider of(@NonNull FragmentActivity activity,
@Nullable Factory factory) {
···
return new ViewModelProvider(activity.getViewModelStore(), factory);
}
public static ViewModelProvider of(@NonNull Fragment fragment,
@Nullable Factory factory) {
···
return new ViewModelProvider(fragment.getViewModelStore(), factory);
}
// for FragmentActivity
Lifecycles 2.0.0-alpha1 (AndroidX)
ViewModelProviders
// for Fragment

42. ViewModelStore
ViewModel2
FragmentA
ViewModel3
ViewModelStore
ViewModel1
ViewModel1
FragmentB
ViewModel2
Created FragmentActivity

43. ViewModelStore
ViewModel2
FragmentA
ViewModel3
ViewModelStore
ViewModel1
FragmentB
Recreated FragmentActivity on rotation

44. ViewModelStore
ViewModel2
FragmentA
ViewModel3
ViewModelStore
ViewModel1
ViewModel1
ViewModelProvider
ViewModelProviders
FragmentB
ViewModel2
Restored ViewModels

45. ViewModelStore
ViewModel2
ViewModel3
ViewModelStore
ViewModel1
FragmentA
ViewModel1
ViewModelProvider
ViewModelProviders
FragmentB
ViewModel2
Restored ViewModels
ViewModelStore
ViewModel2
ViewModel3
ViewModelStore
ViewModel1

46. How to restore ViewModelStore

47. @Override
public final Object onRetainNonConfigurationInstance() {
···
Object custom = onRetainCustomNonConfigurationInstance();
FragmentManagerNonConfig fragments = mFragments.retainNestedNonConfig();
if (fragments == null && mViewModelStore == null && custom == null) {
return null;
}
NonConfigurationInstances nci = new NonConfigurationInstances();
nci.custom = custom;
nci.viewModelStore = mViewModelStore;
nci.fragments = fragments;
return nci;
}
FragmentActivity Retain All fragment state

48. FragmentActivity Restore All fragment state
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
···
NonConfigurationInstances nc =
(NonConfigurationInstances) getLastNonConfigurationInstance();
if (nc != null) {
mViewModelStore = nc.viewModelStore;
}
if (savedInstanceState != null) {
Parcelable p = savedInstanceState.getParcelable(FRAGMENTS_TAG);
mFragments.restoreAllState(p, nc != null ? nc.fragments : null);
···
}

49. FragmentActivity Restore All fragment state
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
···
NonConfigurationInstances nc =
(NonConfigurationInstances) getLastNonConfigurationInstance();
if (nc != null) {
mViewModelStore = nc.viewModelStore;
}
if (savedInstanceState != null) {
Parcelable p = savedInstanceState.getParcelable(FRAGMENTS_TAG);
mFragments.restoreAllState(p, nc != null ? nc.fragments : null);
···
}

50. Restore All fragment state
public void restoreAllState(Parcelable state, FragmentManagerNonConfig
nonConfig) {
mHost.mFragmentManager.restoreAllState(state, nonConfig);
}
FragmentController

51. Restore All fragment state
FragmentController
public void restoreAllState(Parcelable state, FragmentManagerNonConfig
nonConfig) {
mHost.mFragmentManager.restoreAllState(state, nonConfig);
}

52. FragmentManager
void restoreAllState(Parcelable state, FragmentManagerNonConfig nonConfig) {
···
if (nonConfig != null) {
List<Fragment> nonConfigFragments = nonConfig.getFragments();
childNonConfigs = nonConfig.getChildNonConfigs();
viewModelStores = nonConfig.getViewModelStores();
···
mActive = new SparseArray<>(fms.mActive.length);
for (int i=0; i<fms.mActive.length; i++) {
FragmentState fs = fms.mActive[i];
if (fs != null) {
FragmentManagerNonConfig childNonConfig = null;
if (childNonConfigs != null && i < childNonConfigs.size()) {
childNonConfig = childNonConfigs.get(i);
}
ViewModelStore viewModelStore = null;
if (viewModelStores != null && i < viewModelStores.size()) {
viewModelStore = viewModelStores.get(i);
}
Fragment f = fs.instantiate(mHost, mContainer, mParent,
childNonConfig, viewModelStore);
Restore All fragment state

53. ViewModel could do
! Handle configuration changes?

54. ViewModel could do
! Handle configuration changes? Yes!

55. ViewModel could do
! Handle configuration changes? Yes!
! Replace onSaveInstanceState()?

56. ViewModel could do
! Handle configuration changes? Yes!
! Replace onSaveInstanceState()? No!

57. Use ViewModel with onSaveInstanceState
• Survives configuration changes
• Hold lots of data
• Survives configuration changes and process death
• Requires serialization
• Hold small amount of data (less than 50k of data)
All data for Activity UI
Data to reload Activity data
in emergency
ViewModel onSaveInstanceState

58. Use ViewModel with onSaveInstanceState
• Survives configuration changes
• Hold lots of data
• Survives configuration changes and process death
• Requires serialization
• Hold small amount of data (less than 50k of data)
All the user’s data:
User id, first name, last name, birthday,
address, profile images…
User id
ViewModel onSaveInstanceState

59. and Testing

62. https://github.com/mockito/mockito/issues/1013

63. Wiki & Docs
How to use Search feature
• Handling network errors
• ERROR CODE : 1003
• Do something!
•
•

64. Wiki & Docs
How to use Search feature
• Handling network errors
• ERROR CODE : 1003
• Do something!
•
•
Hard to keep document the latest,
whenever requirement changes

65. Why writing Unit tests
! Think of unit tests as documentation for future developers
! Help developers to refactor safely

66. https://www.shutterstock.com
Testing is
not only for you
but also for your colleagues in your next seat

67. Presenter Testing
! Behavior Driven Testing
! Template : Given-When-Then (3A - Arrange-Act-Assert)

68. @Test
fun givenErrorCode1003_whenSearch_shouldHandleError() {
val networkError = NetworkException(1003, "Network Error!")
doThrow(networkError).when(mockSearchRepository).search(INVALID_QUERY)
presenter.search(INVALID_QUERY)
verify(view).hideLoading()
verify(view).setErrorMessage(networkError.message)
}

69. ViewModel Testing
! Assert data values

70. @Test
fun givenErrorCode1003_whenSearch_shouldHandleError() {
val networkError = NetworkException(1003, "Network Error!")
doThrow(networkError).when(mockSearchRepository).search(INVALID_QUERY)
presenter.search(INVALID_QUERY)
verify(view).hideLoading()
verify(view).setErrorMessage(networkError.message)
}
@Test
fun givenErrorCode1003_whenSearch_shouldHandleError() {
···
viewModel.search(INVALID_QUERY)
assertEquals(viewModel.loading.value, false)
assertEquals(viewModel.errorMessage.value, networkError.message)
}
Presenter
ViewModel

71. ViewModel Testing
! Assert data values
! Verify Observer onChanged() events
! Dependency for testing LiveData
! testImplementation “android.arch.core:core-testing:{version}“
! @Rule
val instantTaskExecutorRule = InstantTaskExecutorRule()

72. @Test
fun givenErrorCode1003_whenSearch_shouldHandleError() {
···
val mockObserver = mock<Observer<Boolean>>()
viewModel.loading.observeForever(mockObserver)
viewModel.search(INVALID_QUERY)
assertEquals(viewModel.loading.value, false)
verify(mockObserver).onChanged(false)
}
class SearchActivity : AppCompatActivity() {
viewModel.loading.observe(this, Observer {
it?.let {
if (it) loading.visibility = View.VISIBLE
else loading.visibility = View.GONE
}
})
}
SearchActivity

73. Mockito features
! verify(), reset(), never(), doThrow()
! verifyNoMoreInteractions()
! verifyZeroInteractions()

74. @Test
fun givenErrorCode1003_whenSearch_shouldHandleError() {
···
val mockObserver = mock<Observer<Boolean>>()
viewModel.loading.observeForever(mockObserver)
viewModel.search(INVALID_QUERY)
verify(mockObserver).onChanged(false)
reset(mockObserver)
// For making sure interaction(s) never happened on mock
verifyNoMoreInteractions(mockObserver)
verify(mockObserver, never()).onChanged(any())
// For finding redundant invocations
verifyZeroInteractions(mockData1, mockData2)
}

75. Thank you
@imkimkevin / imkimkevin@gmail.com
Kevin Yongjun Kim

76. References
! https://www.youtube.com/watch?v=5qlIPTDE274
! https://medium.com/google-developers/viewmodels-persistence-
onsaveinstancestate-restoring-ui-state-and-loaders-fc7cc4a6c090
! https://developer.android.com/topic/libraries/architecture/viewmodel