Feature paging

advanced/end/app/build.gradle

@@ -51,6 +51,7 @@ android {
 }
 
 dependencies {
+    implementation freeCompilerArgs += ["-Xopt-in=kotlin.RequiresOptIn"]
     implementation fileTree(dir: 'libs')
     implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:$coroutines"
     implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:$coroutines"

advanced/end/app/src/main/java/com/example/android/codelabs/paging/data/GithubPagingSource.kt

@@ -0,0 +1,44 @@
+// GitHub page API is 1 based: https://developer.github.com/v3/#pagination
+private const val GITHUB_STARTING_PAGE_INDEX = 1
+
+class GithubPagingSource(
+    private val service: GithubService,
+    private val query: String
+) : PagingSource<Int, Repo>() {
+
+    override suspend fun load(params: LoadParams<Int>): LoadResult<Int, Repo> {
+        val position = params.key ?: GITHUB_STARTING_PAGE_INDEX
+        val apiQuery = query + IN_QUALIFIER
+        return try {
+            val response = service.searchRepos(apiQuery, position, params.loadSize)
+            val repos = response.items
+            val nextKey = if (repos.isEmpty()) {
+                null
+            } else {
+                // initial load size = 3 * NETWORK_PAGE_SIZE
+                // ensure we're not requesting duplicating items, at the 2nd request
+                position + (params.loadSize / NETWORK_PAGE_SIZE)
+            }
+            LoadResult.Page(
+                data = repos,
+                prevKey = if (position == GITHUB_STARTING_PAGE_INDEX) null else position - 1,
+                nextKey = nextKey
+            )
+        } catch (exception: IOException) {
+            return LoadResult.Error(exception)
+        } catch (exception: HttpException) {
+            return LoadResult.Error(exception)
+        }
+    }
+    // The refresh key is used for subsequent refresh calls to PagingSource.load after the initial load
+    override fun getRefreshKey(state: PagingState<Int, Repo>): Int? {
+        // We need to get the previous key (or next key if previous is null) of the page
+        // that was closest to the most recently accessed index.
+        // Anchor position is the most recently accessed index
+        return state.anchorPosition?.let { anchorPosition ->
+            state.closestPageToPosition(anchorPosition)?.prevKey?.plus(1)
+                ?: state.closestPageToPosition(anchorPosition)?.nextKey?.minus(1)
+        }
+    }
+
+}

advanced/end/app/src/main/java/com/example/android/codelabs/paging/data/GithubRepository.kt

@@ -26,38 +26,34 @@ import com.example.android.codelabs.paging.db.RepoDatabase
 import com.example.android.codelabs.paging.model.Repo
 import kotlinx.coroutines.flow.Flow
 
-/**
- * Repository class that works with local and remote data sources.
+/** Paging 3 now : )
+ * 1. Handles in-memory cache.
+   2. Requests data when the user is close to the end of the list.
  */
-class GithubRepository(
-    private val service: GithubService,
-    private val database: RepoDatabase
-) {
 
-    /**
-     * Search repositories whose names match the query, exposed as a stream of data that will emit
-     * every time we get more data from the network.
-     */
-    fun getSearchResultStream(query: String): Flow<PagingData<Repo>> {
-        Log.d("GithubRepository", "New query: $query")
+class GithubRepository(private val service: GithubService,
+                       private val database: RepoDatabase
+) {
 
-        // appending '%' so we can allow other characters to be before and after the query string
-        val dbQuery = "%${query.replace(' ', '%')}%"
-        val pagingSourceFactory = { database.reposDao().reposByName(dbQuery) }
+    // appending '%' so we can allow other characters to be before and after the query string
+    val dbQuery = "%${query.replace(' ', '%')}%"
+    val pagingSourceFactory =  { database.reposDao().reposByName(dbQuery)}
 
+    fun getSearchResultStream(query: String): Flow<PagingData<Repo>> {
         @OptIn(ExperimentalPagingApi::class)
         return Pager(
-            config = PagingConfig(pageSize = NETWORK_PAGE_SIZE, enablePlaceholders = false),
-            remoteMediator = GithubRemoteMediator(
-                query,
-                service,
-                database
+            config = PagingConfig(
+                pageSize = NETWORK_PAGE_SIZE,
+                maxSize = NETWORK_MAX_SIZE,
+                enablePlaceholders = false
             ),
+            remoteMediator =  GithubRemoteMediator(service, query, database) }
             pagingSourceFactory = pagingSourceFactory
         ).flow
     }
 
     companion object {
-        const val NETWORK_PAGE_SIZE = 30
+        const val NETWORK_PAGE_SIZE = 50
+        const val NETWORK_MAX_SIZE = 150
     }
 }

advanced/end/app/src/main/java/com/example/android/codelabs/paging/ui/ReposAdapter.kt

@@ -63,7 +63,7 @@ class ReposAdapter : PagingDataAdapter<UiModel, ViewHolder>(UIMODEL_COMPARATOR)
             }
 
             override fun areContentsTheSame(oldItem: UiModel, newItem: UiModel): Boolean =
-                    oldItem == newItem
+                oldItem == newItem
         }
     }
 }

advanced/end/app/src/main/java/com/example/android/codelabs/paging/ui/SearchRepositoriesActivity.kt

@@ -48,12 +48,7 @@ class SearchRepositoriesActivity : AppCompatActivity() {
         setContentView(view)
 
         // get the view model
-        val viewModel = ViewModelProvider(
-            this, Injection.provideViewModelFactory(
-                context = this,
-                owner = this
-            )
-        )
+        val viewModel = ViewModelProvider(this, Injection.provideViewModelFactory(owner = this, context = this))
             .get(SearchRepositoriesViewModel::class.java)
 
         // add dividers between RecyclerView's row items
@@ -74,21 +69,20 @@ class SearchRepositoriesActivity : AppCompatActivity() {
      */
     private fun ActivitySearchRepositoriesBinding.bindState(
         uiState: StateFlow<UiState>,
-        pagingData: Flow<PagingData<UiModel>>,
+        pagingData: Flow<PagingData<Repo>>,
         uiActions: (UiAction) -> Unit
     ) {
         val repoAdapter = ReposAdapter()
-        val header = ReposLoadStateAdapter { repoAdapter.retry() }
         list.adapter = repoAdapter.withLoadStateHeaderAndFooter(
-            header = header,
+            header = ReposLoadStateAdapter { repoAdapter.retry() },
             footer = ReposLoadStateAdapter { repoAdapter.retry() }
         )
+
         bindSearch(
             uiState = uiState,
             onQueryChanged = uiActions
         )
         bindList(
-            header = header,
             repoAdapter = repoAdapter,
             uiState = uiState,
             pagingData = pagingData,
@@ -135,21 +129,21 @@ class SearchRepositoriesActivity : AppCompatActivity() {
     }
 
     private fun ActivitySearchRepositoriesBinding.bindList(
-        header: ReposLoadStateAdapter,
         repoAdapter: ReposAdapter,
         uiState: StateFlow<UiState>,
-        pagingData: Flow<PagingData<UiModel>>,
+        pagingData: Flow<PagingData<Repo>>,
         onScrollChanged: (UiAction.Scroll) -> Unit
     ) {
-        retryButton.setOnClickListener { repoAdapter.retry() }
         list.addOnScrollListener(object : RecyclerView.OnScrollListener() {
             override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
                 if (dy != 0) onScrollChanged(UiAction.Scroll(currentQuery = uiState.value.query))
             }
         })
         val notLoading = repoAdapter.loadStateFlow
-            .asRemotePresentationState()
-            .map { it == RemotePresentationState.PRESENTED }
+            // Only emit when REFRESH LoadState for the paging source changes.
+            .distinctUntilChangedBy { it.source.refresh }
+            // Only react to cases where REFRESH completes i.e., NotLoading.
+            .map { it.source.refresh is LoadState.NotLoading }
 
         val hasNotScrolledForCurrentSearch = uiState
             .map { it.hasNotScrolledForCurrentSearch }
@@ -162,6 +156,19 @@ class SearchRepositoriesActivity : AppCompatActivity() {
         )
             .distinctUntilChanged()
 
+
+        // Collecting from loadStateFlow directly.
+        lifecycleScope.launch {
+            repoAdapter.loadStateFlow.collect { loadState ->
+                val isListEmpty = loadState.refresh is LoadState.NotLoading && repoAdapter.itemCount == 0
+                // show empty list
+                emptyList.isVisible = isListEmpty
+                // Only show the list if refresh succeeds.
+                list.isVisible = !isListEmpty
+            }
+        }
+
+        /*
         lifecycleScope.launch {
             pagingData.collectLatest(repoAdapter::submitData)
         }
@@ -171,38 +178,7 @@ class SearchRepositoriesActivity : AppCompatActivity() {
                 if (shouldScroll) list.scrollToPosition(0)
             }
         }
+        */
 
-        lifecycleScope.launch {
-            repoAdapter.loadStateFlow.collect { loadState ->
-                // Show a retry header if there was an error refreshing, and items were previously
-                // cached OR default to the default prepend state
-                header.loadState = loadState.mediator
-                    ?.refresh
-                    ?.takeIf { it is LoadState.Error && repoAdapter.itemCount > 0 }
-                    ?: loadState.prepend
-
-                val isListEmpty = loadState.refresh is LoadState.NotLoading && repoAdapter.itemCount == 0
-                // show empty list
-                emptyList.isVisible = isListEmpty
-                // Only show the list if refresh succeeds, either from the the local db or the remote.
-                list.isVisible =  loadState.source.refresh is LoadState.NotLoading || loadState.mediator?.refresh is LoadState.NotLoading
-                // Show loading spinner during initial load or refresh.
-                progressBar.isVisible = loadState.mediator?.refresh is LoadState.Loading
-                // Show the retry state if initial load or refresh fails.
-                retryButton.isVisible = loadState.mediator?.refresh is LoadState.Error && repoAdapter.itemCount == 0
-                // Toast on any error, regardless of whether it came from RemoteMediator or PagingSource
-                val errorState = loadState.source.append as? LoadState.Error
-                    ?: loadState.source.prepend as? LoadState.Error
-                    ?: loadState.append as? LoadState.Error
-                    ?: loadState.prepend as? LoadState.Error
-                errorState?.let {
-                    Toast.makeText(
-                        this@SearchRepositoriesActivity,
-                        "\uD83D\uDE28 Wooops ${it.error}",
-                        Toast.LENGTH_LONG
-                    ).show()
-                }
-            }
-        }
     }
 }

advanced/end/app/src/main/java/com/example/android/codelabs/paging/ui/SearchRepositoriesViewModel.kt

@@ -45,22 +45,24 @@ import kotlinx.coroutines.launch
  */
 class SearchRepositoriesViewModel(
     private val repository: GithubRepository,
-    private val savedStateHandle: SavedStateHandle
+    private val savedStateHandle: SavedStateHandle  // SavedStateRegistryOwner
 ) : ViewModel() {
 
     /**
      * Stream of immutable states representative of the UI.
      */
     val state: StateFlow<UiState>
 
-    val pagingDataFlow: Flow<PagingData<UiModel>>
+    val pagingDataFlow: Flow<PagingData<Repo>>
 
     /**
      * Processor of side effects from the UI which in turn feedback into [state]
      */
     val accept: (UiAction) -> Unit
 
     init {
+
+        // UiAction Stream
         val initialQuery: String = savedStateHandle.get(LAST_SEARCH_QUERY) ?: DEFAULT_QUERY
         val lastQueryScrolled: String = savedStateHandle.get(LAST_QUERY_SCROLLED) ?: DEFAULT_QUERY
         val actionStateFlow = MutableSharedFlow<UiAction>()
@@ -80,6 +82,7 @@ class SearchRepositoriesViewModel(
             )
             .onStart { emit(UiAction.Scroll(currentQuery = lastQueryScrolled)) }
 
+        // flows for both PagingData and UiState
         pagingDataFlow = searches
             .flatMapLatest { searchRepo(queryString = it.query) }
             .cachedIn(viewModelScope)
@@ -143,14 +146,16 @@ class SearchRepositoriesViewModel(
 }
 
 sealed class UiAction {
-    data class Search(val query: String) : UiAction()
-    data class Scroll(val currentQuery: String) : UiAction()
+    data class Search(val query: String) : UiAction()    // query
+    data class Scroll(//val currentQuery: String,
+                      val visibleItemCount: Int,
+                      val lastVisibleItemPosition: Int,
+                      val totalItemCount: Int) : UiAction()  // scrolling down the screen to load alot of data
 }
 
 data class UiState(
-    val query: String = DEFAULT_QUERY,
-    val lastQueryScrolled: String = DEFAULT_QUERY,
-    val hasNotScrolledForCurrentSearch: Boolean = false
+    val query: String,
+    val searchResult: RepoSearchResult
 )
 
 sealed class UiModel {

advanced/end/app/src/main/java/com/example/android/codelabs/paging/ui/SeparatorViewHolder.kt

@@ -33,7 +33,7 @@ class SeparatorViewHolder(view: View) : RecyclerView.ViewHolder(view) {
     companion object {
         fun create(parent: ViewGroup): SeparatorViewHolder {
             val view = LayoutInflater.from(parent.context)
-                    .inflate(R.layout.separator_view_item, parent, false)
+                .inflate(R.layout.separator_view_item, parent, false)
             return SeparatorViewHolder(view)
         }
     }

advanced/end/app/src/main/java/com/example/android/codelabs/paging/util/RemotePresentationState.kt

@@ -0,0 +1,3 @@
+enum class RemotePresentationState {
+    INITIAL, REMOTE_LOADING, SOURCE_LOADING, PRESENTED
+}

advanced/start/app/src/main/java/com/example/android/codelabs/paging/Injection.kt

@@ -23,13 +23,13 @@ import com.example.android.codelabs.paging.data.GithubRepository
 import com.example.android.codelabs.paging.ui.ViewModelFactory
 
 /**
- * Class that handles object creation.
+ * Class that handles creation.
  * Like this, objects can be passed as parameters in the constructors and then replaced for
  * testing, where needed.
  */
 object Injection {
 
-    /**
+    /**object
      * Creates an instance of [GithubRepository] based on the [GithubService] and a
      * [GithubLocalCache]
      */

basic/end/settings.gradle

@@ -3,6 +3,14 @@
 // https://docs.gradle.org/current/userguide/platforms.html
 enableFeaturePreview("VERSION_CATALOGS")
 
+pluginManagement {
+    repositories {
+        google()
+        mavenCentral()
+        gradlePluginPortal()
+    }
+}
+
 dependencyResolutionManagement {
     repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
     repositories {