Implement working paging

app/src/androidTest/java/com/karumi/jetpack/superheroes/ui/view/MainActivityTest.kt

@@ -1,5 +1,8 @@
 package com.karumi.jetpack.superheroes.ui.view
 
+import android.os.Looper
+import androidx.paging.PagedList
+import androidx.paging.PositionalDataSource
 import com.karumi.jetpack.superheroes.data.repository.SuperHeroRepository
 import com.karumi.jetpack.superheroes.data.singleValueLiveData
 import com.karumi.jetpack.superheroes.domain.model.SuperHero
@@ -9,6 +12,7 @@ import org.kodein.di.Kodein
 import org.kodein.di.erased.bind
 import org.kodein.di.erased.instance
 import org.mockito.Mock
+import java.util.concurrent.Executors.newSingleThreadExecutor
 
 class MainActivityTest : AcceptanceTest<MainActivity>(MainActivity::class.java) {
 
@@ -64,6 +68,11 @@ class MainActivityTest : AcceptanceTest<MainActivity>(MainActivity::class.java)
  compareScreenshot(activity)
  }
 
+ private fun compareScreenshot(activity: MainActivity) {
+ Thread.sleep(100)
+ super.compareScreenshot(activity)
+ }
+
  private fun givenThereAreSomeAvengers(numberOfAvengers: Int): List<SuperHero> =
  givenThereAreSomeSuperHeroes(numberOfAvengers, areAvengers = true)
 
@@ -84,15 +93,42 @@ class MainActivityTest : AcceptanceTest<MainActivity>(MainActivity::class.java)
  )
  }
 
- whenever(repository.getAllSuperHeroes()).thenReturn(singleValueLiveData(superHeroes))
+ whenever(repository.getAllSuperHeroes())
+ .thenReturn(singleValueLiveData(superHeroes.toPagedList()))
+
  return superHeroes
  }
 
  private fun givenThereAreNoSuperHeroes() {
- whenever(repository.getAllSuperHeroes()).thenReturn(singleValueLiveData(emptyList()))
+ whenever(repository.getAllSuperHeroes())
+ .thenReturn(singleValueLiveData(emptyList<SuperHero>().toPagedList()))
  }
 
  override val testDependencies = Kodein.Module("Test dependencies", allowSilentOverride = true) {
  bind<SuperHeroRepository>() with instance(repository)
  }
+
+ private fun List<SuperHero>.toPagedList(): PagedList<SuperHero> =
+ PagedList.Builder(object : PositionalDataSource<SuperHero>() {
+ override fun loadRange(
+ params: LoadRangeParams,
+ callback: LoadRangeCallback<SuperHero>
+ ) {
+ callback.onResult(this@toPagedList)
+ }
+
+ override fun loadInitial(
+ params: LoadInitialParams,
+ callback: LoadInitialCallback<SuperHero>
+ ) {
+ callback.onResult(
+ this@toPagedList,
+ 0,
+ this@toPagedList.size
+ )
+ }
+ }, 100)
+ .setNotifyExecutor(newSingleThreadExecutor { Looper.getMainLooper().thread })
+ .setFetchExecutor(newSingleThreadExecutor { Looper.getMainLooper().thread })
+ .build()
 }

app/src/main/java/com/karumi/jetpack/superheroes/SuperHeroesApplication.kt

@@ -6,6 +6,7 @@ import com.karumi.jetpack.superheroes.common.module
 import com.karumi.jetpack.superheroes.data.repository.LocalSuperHeroDataSource
 import com.karumi.jetpack.superheroes.data.repository.RemoteSuperHeroDataSource
 import com.karumi.jetpack.superheroes.data.repository.SuperHeroRepository
+import com.karumi.jetpack.superheroes.data.repository.SuperHeroesBoundaryCallback
 import com.karumi.jetpack.superheroes.data.repository.room.SuperHeroDao
 import org.kodein.di.DKodein
 import org.kodein.di.Kodein
@@ -41,9 +42,12 @@ class SuperHeroesApplication : Application(), KodeinAware {
  database.superHeroesDao()
  }
  bind<SuperHeroRepository>() with provider {
- SuperHeroRepository(instance(), instance())
+ SuperHeroRepository(instance(), instance(), instance())
  }
- bind<LocalSuperHeroDataSource>() with singleton {
+ bind<SuperHeroesBoundaryCallback>() with provider {
+ SuperHeroesBoundaryCallback(instance(), instance())
+ }
+ bind<LocalSuperHeroDataSource>() with provider {
  LocalSuperHeroDataSource(instance(), instance())
  }
  bind<RemoteSuperHeroDataSource>() with provider {

app/src/main/java/com/karumi/jetpack/superheroes/data/repository/LocalSuperHeroDataSource.kt

@@ -2,6 +2,8 @@ package com.karumi.jetpack.superheroes.data.repository
 
 import androidx.lifecycle.LiveData
 import androidx.lifecycle.Transformations
+import androidx.paging.LivePagedListBuilder
+import androidx.paging.PagedList
 import com.karumi.jetpack.superheroes.data.repository.room.SuperHeroDao
 import com.karumi.jetpack.superheroes.data.repository.room.SuperHeroEntity
 import com.karumi.jetpack.superheroes.domain.model.SuperHero
@@ -11,14 +13,20 @@ class LocalSuperHeroDataSource(
  private val dao: SuperHeroDao,
  private val executor: ExecutorService
 ) {
- fun getAllSuperHeroes(): LiveData<List<SuperHero>> =
- Transformations.map(dao.getAll()) { it.toSuperHeroes() }
+ fun getAllSuperHeroes(
+ pageSize: Int,
+ boundaryCallback: PagedList.BoundaryCallback<SuperHero>
+ ): LiveData<PagedList<SuperHero>> {
+ val superHeroesFactory = dao.getAll().map { it.toSuperHero() }
+ return LivePagedListBuilder(superHeroesFactory, pageSize)
+ .setBoundaryCallback(boundaryCallback)
+ .build()
+ }
 
  fun get(id: String): LiveData<SuperHero?> =
  Transformations.map(dao.getById(id)) { it?.toSuperHero() }
 
  fun saveAll(all: List<SuperHero>) = executor.execute {
- dao.deleteAll()
  dao.insertAll(all.map { it.toEntity() })
  }
 
@@ -27,7 +35,6 @@ class LocalSuperHeroDataSource(
  return superHero
  }
 
- private fun List<SuperHeroEntity>.toSuperHeroes(): List<SuperHero> = map { it.toSuperHero() }
  private fun SuperHeroEntity.toSuperHero(): SuperHero = superHero
  private fun SuperHero.toEntity(): SuperHeroEntity = SuperHeroEntity(this)
 }

app/src/main/java/com/karumi/jetpack/superheroes/data/repository/RemoteSuperHeroDataSource.kt

@@ -15,11 +15,15 @@ class RemoteSuperHeroDataSource(
  private val superHeroes: MutableMap<String, SuperHero> =
  fakeData().associateBy { it.id }.toMutableMap()
 
- fun getAllSuperHeroes(): LiveData<List<SuperHero>> {
+ fun getSuperHeroesPage(pageIndex: Int, pageSize: Int): LiveData<List<SuperHero>> {
  val allSuperHeroes = MutableLiveData<List<SuperHero>>()
  executor.execute {
  waitABit()
- allSuperHeroes.postValue(superHeroes.values.toList().sortedBy { it.id })
+ val superHeroesPage = superHeroes.values.toList()
+ .sortedBy { it.id }
+ .drop(pageIndex * pageSize)
+ .take(pageSize)
+ allSuperHeroes.postValue(superHeroesPage)
  }
  return allSuperHeroes
  }

app/src/main/java/com/karumi/jetpack/superheroes/data/repository/SuperHeroRepository.kt

@@ -2,23 +2,21 @@ package com.karumi.jetpack.superheroes.data.repository
 
 import androidx.lifecycle.LiveData
 import androidx.lifecycle.MediatorLiveData
+import androidx.paging.PagedList
 import com.karumi.jetpack.superheroes.domain.model.SuperHero
 
 class SuperHeroRepository(
  private val local: LocalSuperHeroDataSource,
- private val remote: RemoteSuperHeroDataSource
+ private val remote: RemoteSuperHeroDataSource,
+ private val boundaryCallback: SuperHeroesBoundaryCallback
 ) {
- fun getAllSuperHeroes(): LiveData<List<SuperHero>> = MediatorLiveData<List<SuperHero>>().apply {
- val localSource = local.getAllSuperHeroes()
- val remoteSource = remote.getAllSuperHeroes()
-
- addSource(remoteSource) { superHeroes ->
- removeSource(remoteSource)
- addSource(localSource) { postValue(it) }
- local.saveAll(superHeroes)
- }
+ companion object {
+ const val PAGE_SIZE = 4
  }
 
+ fun getAllSuperHeroes(): LiveData<PagedList<SuperHero>> =
+ local.getAllSuperHeroes(PAGE_SIZE, boundaryCallback)
+
  fun get(id: String): LiveData<SuperHero?> = MediatorLiveData<SuperHero?>().apply {
  addSource(local.get(id)) {
  if (it == null) {

app/src/main/java/com/karumi/jetpack/superheroes/data/repository/SuperHeroesBoundaryCallback.kt

@@ -0,0 +1,35 @@
+package com.karumi.jetpack.superheroes.data.repository
+
+import androidx.lifecycle.Observer
+import androidx.paging.PagedList
+import com.karumi.jetpack.superheroes.domain.model.SuperHero
+
+class SuperHeroesBoundaryCallback(
+ private val local: LocalSuperHeroDataSource,
+ private val remote: RemoteSuperHeroDataSource
+) : PagedList.BoundaryCallback<SuperHero>() {
+
+ private var pageIndexAboutToLoad = 0
+
+ override fun onZeroItemsLoaded() {
+ pageIndexAboutToLoad = 0
+ loadNextPage()
+ }
+
+ override fun onItemAtEndLoaded(itemAtEnd: SuperHero) {
+ loadNextPage()
+ }
+
+ private fun loadNextPage() {
+ val remoteSuperHeroesPage =
+ remote.getSuperHeroesPage(pageIndexAboutToLoad, SuperHeroRepository.PAGE_SIZE)
+
+ remoteSuperHeroesPage.observeForever(object : Observer<List<SuperHero>> {
+ override fun onChanged(superHeroes: List<SuperHero>) {
+ local.saveAll(superHeroes)
+ remoteSuperHeroesPage.removeObserver(this)
+ pageIndexAboutToLoad++
+ }
+ })
+ }
+}

app/src/main/java/com/karumi/jetpack/superheroes/data/repository/room/SuperHeroDao.kt

@@ -1,6 +1,7 @@
 package com.karumi.jetpack.superheroes.data.repository.room
 
 import androidx.lifecycle.LiveData
+import androidx.paging.DataSource
 import androidx.room.Dao
 import androidx.room.Insert
 import androidx.room.OnConflictStrategy
@@ -10,7 +11,7 @@ import androidx.room.Update
 @Dao
 interface SuperHeroDao {
  @Query("SELECT * FROM superheroes ORDER BY superhero_id ASC")
- fun getAll(): LiveData<List<SuperHeroEntity>>
+ fun getAll(): DataSource.Factory<Int, SuperHeroEntity>
 
  @Query("SELECT * FROM superheroes WHERE superhero_id = :id")
  fun getById(id: String): LiveData<SuperHeroEntity?>

app/src/main/java/com/karumi/jetpack/superheroes/domain/usecase/GetSuperHeroes.kt

@@ -1,9 +1,11 @@
 package com.karumi.jetpack.superheroes.domain.usecase
 
 import androidx.lifecycle.LiveData
+import androidx.paging.PagedList
 import com.karumi.jetpack.superheroes.data.repository.SuperHeroRepository
 import com.karumi.jetpack.superheroes.domain.model.SuperHero
 
 class GetSuperHeroes(private val superHeroesRepository: SuperHeroRepository) {
- operator fun invoke(): LiveData<List<SuperHero>> = superHeroesRepository.getAllSuperHeroes()
+ operator fun invoke(): LiveData<PagedList<SuperHero>> =
+ superHeroesRepository.getAllSuperHeroes()
 }

app/src/main/java/com/karumi/jetpack/superheroes/ui/view/BaseActivity.kt

@@ -28,7 +28,7 @@ abstract class BaseActivity<T : ViewDataBinding> : AppCompatActivity(), KodeinAw
  abstract val toolbarView: Toolbar
  abstract val activityModules: Kodein.Module
  abstract val viewModel: AndroidViewModel
- protected lateinit var binding: T
+ private lateinit var binding: T
 
  override fun onCreate(savedInstanceState: Bundle?) {
  super.onCreate(savedInstanceState)

app/src/main/java/com/karumi/jetpack/superheroes/ui/view/MainActivity.kt

@@ -3,6 +3,7 @@ package com.karumi.jetpack.superheroes.ui.view
 import android.os.Bundle
 import androidx.appcompat.widget.Toolbar
 import androidx.lifecycle.Observer
+import androidx.paging.PagedList
 import androidx.recyclerview.widget.LinearLayoutManager
 import com.karumi.jetpack.superheroes.R
 import com.karumi.jetpack.superheroes.common.bindViewModel
@@ -32,7 +33,7 @@ class MainActivity : BaseActivity<MainActivityBinding>() {
  initializeRecyclerView()
  viewModel.prepare()
  viewModel.idOfSuperHeroToOpen.observe(this, Observer<String> { openDetail(it) })
- viewModel.superHeroes.observe(this, Observer<List<SuperHero>> { showSuperHeroes(it) })
+ viewModel.superHeroes.observe(this, Observer<PagedList<SuperHero>> { showSuperHeroes(it) })
  }
 
  override fun configureBinding(binding: MainActivityBinding) {
@@ -49,10 +50,8 @@ class MainActivity : BaseActivity<MainActivityBinding>() {
  recycler_view.adapter = adapter
  }
 
- private fun showSuperHeroes(superHeroes: List<SuperHero>) {
- adapter.clear()
- adapter.addAll(superHeroes)
- adapter.notifyDataSetChanged()
+ private fun showSuperHeroes(superHeroes: PagedList<SuperHero>) {
+ adapter.submitList(superHeroes)
  }
 
  private fun openDetail(id: String) {

app/src/main/java/com/karumi/jetpack/superheroes/ui/view/adapter/SuperHeroesAdapter.kt

@@ -3,21 +3,16 @@ package com.karumi.jetpack.superheroes.ui.view.adapter
 import android.view.LayoutInflater
 import android.view.ViewGroup
 import androidx.databinding.DataBindingUtil
-import androidx.recyclerview.widget.RecyclerView
+import androidx.paging.PagedListAdapter
+import androidx.recyclerview.widget.DiffUtil
 import com.karumi.jetpack.superheroes.R
 import com.karumi.jetpack.superheroes.databinding.SuperHeroRowBinding
 import com.karumi.jetpack.superheroes.domain.model.SuperHero
 import com.karumi.jetpack.superheroes.ui.viewmodel.SuperHeroesViewModel
 
 internal class SuperHeroesAdapter(
  private val viewModel: SuperHeroesViewModel
-) : RecyclerView.Adapter<SuperHeroViewHolder>() {
- private val superHeroes: MutableList<SuperHero> = ArrayList()
-
- fun addAll(collection: Collection<SuperHero>) {
- superHeroes.addAll(collection)
- }
-
+) : PagedListAdapter<SuperHero, SuperHeroViewHolder>(diffCallback) {
  override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): SuperHeroViewHolder {
  val binding: SuperHeroRowBinding = DataBindingUtil.inflate(
  LayoutInflater.from(parent.context),
@@ -30,14 +25,17 @@ internal class SuperHeroesAdapter(
  }
 
  override fun onBindViewHolder(holder: SuperHeroViewHolder, position: Int) {
- holder.render(superHeroes[position], viewModel)
+ val superHero = getItem(position) ?: return
+ holder.render(superHero, viewModel)
  }
 
- override fun getItemCount(): Int {
- return superHeroes.size
- }
+ companion object {
+ private val diffCallback = object : DiffUtil.ItemCallback<SuperHero>() {
+ override fun areItemsTheSame(oldItem: SuperHero, newItem: SuperHero): Boolean =
+ oldItem.id == newItem.id
 
- fun clear() {
- superHeroes.clear()
+ override fun areContentsTheSame(oldItem: SuperHero, newItem: SuperHero): Boolean =
+ oldItem == newItem
+ }
  }
 }

app/src/main/java/com/karumi/jetpack/superheroes/ui/viewmodel/SuperHeroesViewModel.kt

@@ -4,6 +4,7 @@ import android.app.Application
 import androidx.lifecycle.AndroidViewModel
 import androidx.lifecycle.MediatorLiveData
 import androidx.lifecycle.MutableLiveData
+import androidx.paging.PagedList
 import com.karumi.jetpack.superheroes.domain.model.SuperHero
 import com.karumi.jetpack.superheroes.domain.usecase.GetSuperHeroes
 import com.karumi.jetpack.superheroes.ui.view.SingleLiveEvent
@@ -15,7 +16,7 @@ class SuperHeroesViewModel(
 
  val isLoading = MutableLiveData<Boolean>()
  val isShowingEmptyCase = MutableLiveData<Boolean>()
- val superHeroes = MediatorLiveData<List<SuperHero>>()
+ val superHeroes = MediatorLiveData<PagedList<SuperHero>>()
  val idOfSuperHeroToOpen = SingleLiveEvent<String>()
 
  fun prepare() {