ScrollListener to load more articles, change state of list on changing category.

Author: RajashekarRaju

app/src/main/java/com/developerbreach/developerbreach/view/category/CategoryBindingAdapter.kt

@@ -20,7 +20,7 @@ fun MaterialCardView.setItemCategoryParentListener(
     viewModel: ArticleListViewModel,
 ) {
     this.setOnClickListener {
-        viewModel.getArticlesBasedOnCategoryId(category)
+        viewModel.saveUserSelectedCategory(category)
     }
 }
 

app/src/main/java/com/developerbreach/developerbreach/view/list/ArticleListBindingAdapter.kt

@@ -19,23 +19,51 @@ import com.developerbreach.developerbreach.utils.capitalizeWord
 import com.google.android.material.card.MaterialCardView
 
 
-@BindingAdapter("bindArticlesListDataByCategory")
+@BindingAdapter(
+    "bindArticlesListDataByCategory",
+    "bindArticleListViewModel",
+)
 fun RecyclerView.setArticleListDataByCategory(
-    list: List<Article>?
+    list: List<Article>?,
+    viewModel: ArticleListViewModel
 ) {
     val adapter = ArticleAdapter()
     // Pass list to adapter calling submitList since our adapter class extends to ListAdapter<>.
     adapter.submitList(list)
     // Set adapter with recyclerView.
     this.adapter = adapter
 
+    this.addOnScrollListener(articlesScrollListener(viewModel))
+
     if (list?.isNotEmpty() == true) {
         this.visibility = View.VISIBLE
     } else {
         this.visibility = View.GONE
     }
 }
 
+private var isFirstTimeCall = true
+
+private fun articlesScrollListener(
+    viewModel: ArticleListViewModel
+): RecyclerView.OnScrollListener = object : RecyclerView.OnScrollListener() {
+
+    override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
+        super.onScrollStateChanged(recyclerView, newState)
+
+        if (!recyclerView.canScrollVertically(1) && newState == RecyclerView.SCROLL_STATE_IDLE) {
+            if (isFirstTimeCall) {
+                isFirstTimeCall = false
+                viewModel.loadMoreArticles()
+            }
+        }
+
+        if (!recyclerView.canScrollVertically(1) && newState == RecyclerView.SCROLL_STATE_DRAGGING) {
+            isFirstTimeCall = true
+        }
+    }
+}
+
 
 @BindingAdapter("bindSelectedCategoryText")
 fun TextView.setSelectedCategoryText(
@@ -109,7 +137,7 @@ fun MaterialCardView.setArticleToDetailClickListener(
     card.setOnClickListener {
         TransitionManager.beginDelayedTransition(card, Fade())
         title.visibility = View.GONE
-        AppNavDirections(findNavController()).articlesListToDetail(articleId, card)
+        AppNavDirections(findNavController()).fragmentsToDetailFragment(articleId, card)
     }
 }
 

app/src/main/java/com/developerbreach/developerbreach/view/list/ArticleListViewModel.kt

@@ -41,6 +41,16 @@ class ArticleListViewModel constructor(
     val articlesState: LiveData<DataState>
         get() = _articlesState
 
+    private var loadNextPage: Int = 1
+
+    private lateinit var selectedCategory: Categories
+
+    fun saveUserSelectedCategory(category: Categories) {
+        loadNextPage = 1
+        selectedCategory = category
+        loadArticlesWithSelectedCategory()
+    }
+
     init {
         launchToLoadCategoriesData()
     }
@@ -59,14 +69,22 @@ class ArticleListViewModel constructor(
         }
     }
 
-    fun getArticlesBasedOnCategoryId(
-        category: Categories
-    ) {
+    fun loadMoreArticles() {
+        loadNextPage += 1
+        loadArticlesWithSelectedCategory()
+        Timber.e("Current page $loadNextPage")
+    }
+
+    private fun loadArticlesWithSelectedCategory() {
         viewModelScope.launch {
             _articlesState.value = DataState.LOADING
             try {
-                _articles.postValue(repository.getArticlesByCategoryId(category.categoryId))
-                _selectedCategoryName.postValue(category.categoryName)
+                val articlesById = repository.getArticlesByCategory(
+                    selectedCategory.categoryId,
+                    loadNextPage
+                )
+                _articles.postValue(articlesById)
+                _selectedCategoryName.postValue(selectedCategory.categoryName)
                 _articlesState.value = DataState.DONE
             } catch (e: Exception) {
                 Timber.e("Exception caught in ArticleListViewModel ${e.message}")

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

@@ -115,16 +115,15 @@
                 android:orientation="vertical"
                 android:paddingTop="12dp"
                 android:scrollbars="none"
+                app:bindArticleListViewModel="@{viewModel}"
                 app:bindArticlesListDataByCategory="@{viewModel.articlesByCategory}"
                 app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
                 app:layout_constraintBottom_toBottomOf="parent"
                 app:layout_constraintStart_toStartOf="parent"
                 app:layout_constraintTop_toBottomOf="@id/hor_line_category"
-                app:reverseLayout="true"
-                app:stackFromEnd="true"
                 tools:itemCount="6"
                 tools:listitem="@layout/item_article"
-                tools:visibility="gone" />
+                tools:visibility="invisible" />
 
             <ImageView
                 android:id="@+id/select_category_background_image_view"