Fix part #632: Replace current recyclerview implementation with Binda…

…bleAdapter usage. (#641)

* working on topic practice.

* reverted

* updated implementation

* Update ContinuePlayingFragmentPresenter.kt

* Update ContinuePlayingFragmentPresenter.kt

* Update ContinuePlayingItemViewModel.kt

* Delete OngoingListAdapter.kt

* nit change

* Update ContinuePlayViewModel.kt

* fixed nit

app/src/main/java/org/oppia/app/home/continueplaying/ContinuePlayViewModel.kt

@@ -0,0 +1,56 @@
+package org.oppia.app.home.continueplaying
+
+import androidx.fragment.app.Fragment
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.Transformations
+import androidx.lifecycle.ViewModel
+import org.oppia.app.R
+import org.oppia.app.model.OngoingStoryList
+import org.oppia.domain.topic.TopicListController
+import org.oppia.util.data.AsyncResult
+import javax.inject.Inject
+
+// TODO(#297): Add download status information to promoted-story-card.
+
+/** [ViewModel] for displaying a promoted story. */
+class ContinuePlayViewModel @Inject constructor(
+  private val fragment: Fragment,
+  private val topicListController: TopicListController
+) : ContinuePlayingItemViewModel() {
+
+  private val itemList: MutableList<ContinuePlayingItemViewModel> = ArrayList()
+
+  private val ongoingStoryListSummaryResultLiveData: LiveData<AsyncResult<OngoingStoryList>> by lazy {
+    topicListController.getOngoingStoryList()
+  }
+
+  val ongoingStoryLiveData: LiveData<List<ContinuePlayingItemViewModel>>by lazy {
+    Transformations.map(ongoingStoryListSummaryResultLiveData, ::processOngoingStoryList)
+  }
+
+  private fun processOngoingStoryList(ongoingStoryList: AsyncResult<OngoingStoryList>): List<ContinuePlayingItemViewModel> {
+    if (ongoingStoryList.isSuccess()) {
+      if (ongoingStoryList.getOrThrow().recentStoryList.isNotEmpty()) {
+        val recentSectionTitleViewModel =
+          SectionTitleViewModel(fragment.getString(R.string.ongoing_story_last_week), false)
+        itemList.add(recentSectionTitleViewModel)
+        for (promotedStory in ongoingStoryList.getOrThrow().recentStoryList) {
+          val ongoingStoryViewModel = OngoingStoryViewModel(promotedStory, fragment as OngoingStoryClickListener)
+          itemList.add(ongoingStoryViewModel)
+        }
+      }
+
+      if (ongoingStoryList.getOrThrow().olderStoryList.isNotEmpty()) {
+        val showDivider = itemList.isNotEmpty()
+        val olderSectionTitleViewModel =
+          SectionTitleViewModel(fragment.getString(R.string.ongoing_story_last_month), showDivider)
+        itemList.add(olderSectionTitleViewModel)
+        for (promotedStory in ongoingStoryList.getOrThrow().olderStoryList) {
+          val ongoingStoryViewModel = OngoingStoryViewModel(promotedStory, fragment as OngoingStoryClickListener)
+          itemList.add(ongoingStoryViewModel)
+        }
+      }
+    }
+    return itemList
+  }
+}

app/src/main/java/org/oppia/app/home/continueplaying/ContinuePlayingFragmentPresenter.kt

@@ -5,17 +5,16 @@ import android.view.View
 import android.view.ViewGroup
 import androidx.appcompat.app.AppCompatActivity
 import androidx.fragment.app.Fragment
-import androidx.lifecycle.LiveData
 import androidx.lifecycle.Observer
-import androidx.lifecycle.Transformations
-import org.oppia.app.R
 import org.oppia.app.databinding.ContinuePlayingFragmentBinding
+import org.oppia.app.databinding.OngoingStoryCardBinding
+import org.oppia.app.databinding.SectionTitleBinding
 import org.oppia.app.fragment.FragmentScope
 import org.oppia.app.home.RouteToExplorationListener
-import org.oppia.app.model.OngoingStoryList
 import org.oppia.app.model.PromotedStory
+import org.oppia.app.recyclerview.BindableAdapter
+import org.oppia.app.viewmodel.ViewModelProvider
 import org.oppia.domain.exploration.ExplorationDataController
-import org.oppia.domain.topic.TopicListController
 import org.oppia.util.data.AsyncResult
 import org.oppia.util.logging.Logger
 import javax.inject.Inject
@@ -27,71 +26,56 @@ class ContinuePlayingFragmentPresenter @Inject constructor(
   private val fragment: Fragment,
   private val logger: Logger,
   private val explorationDataController: ExplorationDataController,
-  private val topicListController: TopicListController
+  private val viewModelProvider: ViewModelProvider<ContinuePlayViewModel>
 ) {
 
   private val routeToExplorationListener = activity as RouteToExplorationListener
 
   private lateinit var binding: ContinuePlayingFragmentBinding
 
-  private lateinit var ongoingListAdapter: OngoingListAdapter
-
-  private val itemList: MutableList<ContinuePlayingItemViewModel> = ArrayList()
-
   fun handleCreateView(inflater: LayoutInflater, container: ViewGroup?): View? {
     binding = ContinuePlayingFragmentBinding.inflate(inflater, container, /* attachToRoot= */ false)
-
+    val viewModel = getContinuePlayModel()
     binding.continuePlayingToolbar.setNavigationOnClickListener {
       (activity as ContinuePlayingActivity).finish()
     }
 
-    ongoingListAdapter = OngoingListAdapter(itemList)
-
     binding.ongoingStoryRecyclerView.apply {
-      adapter = ongoingListAdapter
+      adapter = createRecyclerViewAdapter()
     }
     binding.let {
       it.lifecycleOwner = fragment
+      it.viewModel = viewModel
     }
-
-    subscribeToOngoingStoryList()
-
     return binding.root
   }
 
-  private val ongoingStoryListSummaryResultLiveData: LiveData<AsyncResult<OngoingStoryList>> by lazy {
-    topicListController.getOngoingStoryList()
-  }
-
-  private fun subscribeToOngoingStoryList() {
-    getAssumedSuccessfulOngoingStoryList().observe(fragment, Observer<OngoingStoryList> { it ->
-      if (it.recentStoryCount > 0) {
-        val recentSectionTitleViewModel =
-          SectionTitleViewModel(activity.getString(R.string.ongoing_story_last_week), false)
-        itemList.add(recentSectionTitleViewModel)
-        for (promotedStory in it.recentStoryList) {
-          val ongoingStoryViewModel = OngoingStoryViewModel(promotedStory, fragment as OngoingStoryClickListener)
-          itemList.add(ongoingStoryViewModel)
-        }
-      }
-
-      if (it.olderStoryCount > 0) {
-        val showDivider = itemList.isNotEmpty()
-        val olderSectionTitleViewModel =
-          SectionTitleViewModel(activity.getString(R.string.ongoing_story_last_month), showDivider)
-        itemList.add(olderSectionTitleViewModel)
-        for (promotedStory in it.olderStoryList) {
-          val ongoingStoryViewModel = OngoingStoryViewModel(promotedStory, fragment as OngoingStoryClickListener)
-          itemList.add(ongoingStoryViewModel)
+  private fun createRecyclerViewAdapter(): BindableAdapter<ContinuePlayingItemViewModel> {
+    return BindableAdapter.MultiTypeBuilder
+      .newBuilder<ContinuePlayingItemViewModel, ContinuePlayingItemViewModel.ViewType> { viewModel ->
+        when (viewModel) {
+          is SectionTitleViewModel -> ContinuePlayingItemViewModel.ViewType.VIEW_TYPE_SECTION_TITLE_TEXT
+          is OngoingStoryViewModel -> ContinuePlayingItemViewModel.ViewType.VIEW_TYPE_SECTION_STORY_ITEM
+          else -> throw IllegalArgumentException("Encountered unexpected view model: $viewModel")
         }
       }
-      ongoingListAdapter.notifyDataSetChanged()
-    })
+      .registerViewDataBinder(
+        viewType = ContinuePlayingItemViewModel.ViewType.VIEW_TYPE_SECTION_TITLE_TEXT,
+        inflateDataBinding = SectionTitleBinding::inflate,
+        setViewModel = SectionTitleBinding::setViewModel,
+        transformViewModel = { it as SectionTitleViewModel }
+      )
+      .registerViewDataBinder(
+        viewType = ContinuePlayingItemViewModel.ViewType.VIEW_TYPE_SECTION_STORY_ITEM,
+        inflateDataBinding = OngoingStoryCardBinding::inflate,
+        setViewModel = OngoingStoryCardBinding::setViewModel,
+        transformViewModel = { it as OngoingStoryViewModel }
+      )
+      .build()
   }
 
-  private fun getAssumedSuccessfulOngoingStoryList(): LiveData<OngoingStoryList> {
-    // If there's an error loading the data, assume the default.
-    return Transformations.map(ongoingStoryListSummaryResultLiveData) { it.getOrDefault(OngoingStoryList.getDefaultInstance()) }
+  private fun getContinuePlayModel(): ContinuePlayViewModel {
+    return viewModelProvider.getForFragment(fragment, ContinuePlayViewModel::class.java)
   }
 
   fun onOngoingStoryClicked(promotedStory: PromotedStory) {

app/src/main/java/org/oppia/app/home/continueplaying/ContinuePlayingItemViewModel.kt

@@ -2,5 +2,10 @@ package org.oppia.app.home.continueplaying
 
 import org.oppia.app.viewmodel.ObservableViewModel
 
-/** The root [ViewModel] for all individual items that may be displayed in continue-playing fragment recycler view. */
-abstract class ContinuePlayingItemViewModel: ObservableViewModel()
+/** The root  [ViewModel] for all individual items that may be displayed in [ContinuePlayingFragment] [RecyclerView]. */
+abstract class ContinuePlayingItemViewModel : ObservableViewModel() {
+  enum class ViewType {
+    VIEW_TYPE_SECTION_TITLE_TEXT,
+    VIEW_TYPE_SECTION_STORY_ITEM
+  }
+}

app/src/main/res/layout/continue_playing_fragment.xml

@@ -2,6 +2,13 @@
 <layout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:app="http://schemas.android.com/apk/res-auto">
 
+  <data>
+
+    <variable
+      name="viewModel"
+      type="org.oppia.app.home.continueplaying.ContinuePlayViewModel" />
+  </data>
+
   <androidx.constraintlayout.widget.ConstraintLayout
     android:layout_width="match_parent"
     android:layout_height="match_parent"
@@ -47,6 +54,7 @@
         android:paddingTop="8dp"
         android:paddingBottom="172dp"
         android:scrollbars="none"
+        app:data="@{viewModel.ongoingStoryLiveData}"
         app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager" />
 
       <View