Eduardo Medina

MVVM Pattern

Model View ViewModel

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MVC Model View Controller

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MVP Model View Presenter

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Clean Architecture

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MVVM Model View ViewModel

Architecture Patterns & Architectures

• Delegate responsibilities to other components. (BL, Data layer, View layer)
• Consider the lifecycle of android components.
• Convert your views to Passive Views.
• Define a rule of dependencies.
• Possibility to refactor and support changes.
• Easier to create Unit tests.

You should use some architecture pattern...

Kotlin MVVM Pattern

Kotlin-First

Google goes Kotlin-First

Google I/O 19 �Kotlin-first

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Kotlin v1.3

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Kotlin v1.2

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Google I/O 17

Support Kotlin

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Kotlin 1.0

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Jetbrains

Kotlin

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- 2019

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- 2018

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- 2017

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- 2017

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- 2016

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- 2011

MVVM

MVVM - Model View ViewModel

Callbacks

Property changed events

UI events

Android Jetpack

Architecture

MVVM

Model

LiveData

request data

Callbacks

Repository

Data source

Entity

interface OperationCallback {

fun onSuccess(obj:Any?)

fun onError(obj:Any?)

}

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interface MuseumDataSource {

fun retrieveMuseums(callback: OperationCallback)

fun cancel()

}

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class MuseumRepository:MuseumDataSource {

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override fun retrieveMuseums(callback: OperationCallback) {

… }

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override fun cancel() {

… }

}

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Model

MVVM

ViewModel

ViewModel provides data for UI components and survive configuration changes.

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class ViewModelFactory(private val repository:MuseumDataSource):ViewModelProvider.Factory {

override fun <T : ViewModel?> create(modelClass: Class<T>): T {

return MuseumViewModel(repository) as T

}

}

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class MuseumViewModel(private val repository: MuseumDataSource):ViewModel() {

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private val _isViewLoading=MutableLiveData<Boolean>()

val isViewLoading:LiveData<Boolean> = _isViewLoading

…

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_isViewLoading.postValue(false)

}

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private fun setupViewModel(){

viewModel = ViewModelProviders.of(this,ViewModelFactory(Injection.providerRepository())).get(MuseumViewModel::class.java)

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viewModel.isViewLoading.observe(this,isViewLoadingObserver)

}

ViewModel

MVVM

View

Observers

UI events

LiveData

Property changed events

LiveData & Lifecycle

LiveData & Lifecycle

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private fun setupViewModel(){

viewModel = ViewModelProviders.of(this,ViewModelFactory(Injection.providerRepository())).get(MuseumViewModel::class.java)

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viewModel.museums.observe(this,renderMuseums)

viewModel.isViewLoading.observe(this,isViewLoadingObserver)

viewModel.onMessageError.observe(this,onMessageErrorObserver)

}

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private val renderMuseums= Observer<List<Museum>> {

layoutError.visibility=View.GONE

layoutEmpty.visibility=View.GONE

adapter.update(it)

}

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private val isViewLoadingObserver= Observer<Boolean> {

val visibility=if(it)View.VISIBLE else View.GONE

progressBar.visibility= visibility

}

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private val onMessageErrorObserver= Observer<Any> {

layoutError.visibility=View.VISIBLE

layoutEmpty.visibility=View.GONE

textViewError.text= "Error $it"

}

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override fun onResume() {

super.onResume()

viewModel.loadMuseums()

}

View

Demo

https://github.com/emedinaa/kotlin-mvvm

Architecture

Flow

View behavior

Property changed events

UI events

Request data

Callbacks

Observers

LiveData

Data source

Unit Tests

• Local tests
• Instrumentation tests

Unit tests

JUnit v4.12 + Mockito v2.27.0 + ArchTesting v1.1.1

dependencies {

implementation fileTree(dir: 'libs', include: ['*.jar'])

...

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testImplementation "junit:junit:$junitVersion"

testImplementation "org.mockito:mockito-core:$mockitoVersion"

testImplementation "android.arch.core:core-testing:$archTestingVersion"

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androidTestImplementation "androidx.test:runner:$runnerVersion"

androidTestImplementation "androidx.test.espresso:espresso-core:$espressoVersion"

androidTestImplementation "org.mockito:mockito-core:$mockitoVersion"

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implementation "androidx.lifecycle:lifecycle-extensions:$archLifecycleVersion"

kapt "androidx.lifecycle:lifecycle-compiler:$archLifecycleVersion"

…

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Dependencies

class MVVMUnitTest {

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@Mock private lateinit var repository: MuseumDataSource

@Mock private lateinit var context: Application

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@Captor

private lateinit var operationCallbackCaptor: ArgumentCaptor<OperationCallback>

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private lateinit var viewModel:MuseumViewModel

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private lateinit var isViewLoadingObserver:Observer<Boolean>

private lateinit var onMessageErrorObserver:Observer<Any>

private lateinit var emptyListObserver:Observer<Boolean>

private lateinit var onRenderMuseumsObserver:Observer<List<Museum>>

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private lateinit var museumEmptyList:List<Museum>

private lateinit var museumList:List<Museum>

…

MVVMUnitTest - @Mock / @Captor

class MVVMUnitTest {

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private lateinit var viewModel:MuseumViewModel

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@get:Rule

val rule = InstantTaskExecutorRule()

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@Before

fun setup() {

MockitoAnnotations.initMocks(this)

`when`<Context>(context.applicationContext).thenReturn(context)

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viewModel= MuseumViewModel(repository)

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mockData()

setupObservers()

}

…

MVVMUnitTest - ViewModel & Model

private fun setupObservers(){

isViewLoadingObserver= mock(Observer::class.java) as Observer<Boolean>

onMessageErrorObserver= mock(Observer::class.java) as Observer<Any>

emptyListObserver= mock(Observer::class.java) as Observer<Boolean>

onRenderMuseumsObserver= mock(Observer::class.java)as Observer<List<Museum>>

}

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private fun mockData(){

museumEmptyList= emptyList()

val mockList:MutableList<Museum> = mutableListOf()

mockList.add(Museum(0,"Museo Nacional de Arqueología, Antropología e Historia del Perú",""))

mockList.add(Museum(1,"Museo de Sitio Pachacamac",""))

mockList.add(Museum(2,"Casa Museo José Carlos Mariátegui",""))

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museumList= mockList.toList()

}

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MVVMUnitTest - Observers & Mock data

@Test

fun museumListRepositoryAndViewModel(){

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with(viewModel){

loadMuseums()

isViewLoading.observeForever(isViewLoadingObserver)

museums.observeForever(onRenderMuseumsObserver)

}

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verify(repository, times(1)).retrieveMuseums(capture(operationCallbackCaptor))

operationCallbackCaptor.value.onSuccess(museumList)

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Assert.assertNotNull(viewModel.isViewLoading.value)

Assert.assertTrue(viewModel.museums.value?.size==3)

}

​

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MVVMUnitTest - @Test

@Test

fun museumFailRepositoryAndViewModel() {

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with(viewModel){

loadMuseums()

isViewLoading.observeForever(isViewLoadingObserver)

onMessageError.observeForever(onMessageErrorObserver)

}

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verify(repository, times(1)).retrieveMuseums(capture(operationCallbackCaptor))

operationCallbackCaptor.value.onError("Ocurrió un error")

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Assert.assertNotNull(viewModel.isViewLoading.value)

Assert.assertNotNull(viewModel.onMessageError.value)

}

​

​

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MVVMUnitTest - @Test

Summary

• ViewModel provides data to UI components.
• Use LiveData for communication between ViewModel and View.
• Don’t use the activity reference on the ViewModel component.
• You can use Mockito with Kotlin but with some considerations.
• Use repository or data source interface for mock the layer data.
• The LiveData components can be mocked.

Summary

https://github.com/emedinaa/kotlin-mvvm

Next ->

• Sealed classes to replace callbacks
• Manage asynchronous processes as synchronous processes with coroutines.
• Integrate ViewModel component and retrofit library with coroutines.
• Dependency injections ? Koin

Next

Show me �the code </>

• Kotlin mvvm + tests https://github.com/emedinaa/kotlin-mvvm/tree/master
• Kotlin mvvm + koin + tests

https://github.com/emedinaa/kotlin-mvvm/tree/koin

• Kotlin mvvm + coroutines + sealed class + tests

https://github.com/emedinaa/kotlin-mvvm/tree/coroutines

Kotlin mvvm samples

https://github.com/emedinaa/kotlin-mvvm

Eduardo Medina

Thank you

@eduardomedina | emedinaa@gmail.com | github/emedinaa |

Android

Dev�Perú

https://www.facebook.com/groups/androidpe/