Step 2 - Migrate to Paging 3.0

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

@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.android.codelabs.paging.data
+
+import androidx.paging.PagingSource
+import com.example.android.codelabs.paging.api.GithubService
+import com.example.android.codelabs.paging.api.IN_QUALIFIER
+import com.example.android.codelabs.paging.model.Repo
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import retrofit2.HttpException
+import java.io.IOException
+
+// GitHub page API is 1 based: https://developer.github.com/v3/#pagination
+private const val GITHUB_STARTING_PAGE_INDEX = 1
+
+@ExperimentalCoroutinesApi
+class GithubPagingSource(
+        private val service: GithubService,
+        private val query: String
+) : PagingSource<Int, Repo>() {
+    override suspend fun load(params: LoadParams<Int>): LoadResult<Int, Repo> {
+        val currentPage = params.key ?: GITHUB_STARTING_PAGE_INDEX
+        val apiQuery = query + IN_QUALIFIER
+        try {
+            val apiResponse = service.searchRepos(apiQuery, currentPage, params.loadSize)
+            return if (apiResponse.isSuccessful) {
+                val repos = apiResponse.body()?.items ?: emptyList()
+                LoadResult.Page(
+                        data = repos,
+                        prevKey = if (currentPage == GITHUB_STARTING_PAGE_INDEX) null else currentPage - 1,
+                        // if we don't get any results, we consider that we're at the last page
+                        nextKey = if (repos.isEmpty()) null else currentPage + 1
+                )
+            } else {
+                LoadResult.Error(IOException(apiResponse.message()))
+            }
+        } catch (exception: IOException) {
+            return LoadResult.Error(exception)
+        } catch (exception: HttpException) {
+            return LoadResult.Error(exception)
+        }
+    }
+}

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

@@ -17,107 +17,31 @@
 package com.example.android.codelabs.paging.data
 
 import android.util.Log
+import androidx.paging.PagingConfig
+import androidx.paging.PagingData
+import androidx.paging.PagingDataFlow
 import com.example.android.codelabs.paging.api.GithubService
-import com.example.android.codelabs.paging.api.IN_QUALIFIER
 import com.example.android.codelabs.paging.model.Repo
-import com.example.android.codelabs.paging.model.RepoSearchResult
 import kotlinx.coroutines.ExperimentalCoroutinesApi
-import kotlinx.coroutines.FlowPreview
-import kotlinx.coroutines.channels.ConflatedBroadcastChannel
 import kotlinx.coroutines.flow.Flow
-import kotlinx.coroutines.flow.asFlow
-import retrofit2.HttpException
-import java.io.IOException
-
-// GitHub page API is 1 based: https://developer.github.com/v3/#pagination
-private const val GITHUB_STARTING_PAGE_INDEX = 1
 
 /**
  * Repository class that works with local and remote data sources.
  */
 @ExperimentalCoroutinesApi
 class GithubRepository(private val service: GithubService) {
 
-    // keep the list of all results received
-    private val inMemoryCache = mutableListOf<Repo>()
-
-    // keep channel of results. The channel allows us to broadcast updates so
-    // the subscriber will have the latest data
-    private val searchResults = ConflatedBroadcastChannel<RepoSearchResult>()
-
-    // keep the last requested page. When the request is successful, increment the page number.
-    private var lastRequestedPage = GITHUB_STARTING_PAGE_INDEX
-
-    // avoid triggering multiple requests in the same time
-    private var isRequestInProgress = false
-
     /**
      * 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.
      */
-    suspend fun getSearchResultStream(query: String): Flow<RepoSearchResult> {
+    fun getSearchResultStream(query: String): Flow<PagingData<Repo>> {
         Log.d("GithubRepository", "New query: $query")
-        lastRequestedPage = 1
-        requestAndSaveData(query)
-
-        return searchResults.asFlow()
-    }
-
-    suspend fun requestMore(query: String) {
-        if (isRequestInProgress) return
-        val successful = requestAndSaveData(query)
-        if (successful) {
-            lastRequestedPage++
-        }
-    }
-
-    suspend fun retry(query: String) {
-        if (isRequestInProgress) return
-        requestAndSaveData(query)
-    }
-
-    private suspend fun requestAndSaveData(query: String): Boolean {
-        isRequestInProgress = true
-        var successful = false
-
-        val apiQuery = query + IN_QUALIFIER
-        try {
-            val response = service.searchRepos(apiQuery, lastRequestedPage, NETWORK_PAGE_SIZE)
-            Log.d("GithubRepository", "response $response")
-            if (response.isSuccessful) {
-                if (response.isSuccessful) {
-                    val repos = response.body()?.items ?: emptyList()
-                    inMemoryCache.addAll(repos)
-                    val reposByName = reposByName(query)
-                    searchResults.offer(RepoSearchResult.Success(reposByName))
-                    successful = true
-                } else {
-                    Log.d("GithubRepository", "fail to get data")
-                    searchResults.offer(RepoSearchResult.Error(IOException(response.message()
-                            ?: "Unknown error")))
-                }
-            } else {
-                Log.d("GithubRepository", "fail to get data")
-                searchResults.offer(RepoSearchResult.Error(IOException(response.message()
-                        ?: "Unknown error")))
-            }
-        } catch (exception: IOException) {
-            searchResults.offer(RepoSearchResult.Error(exception))
-        } catch (exception: HttpException) {
-            searchResults.offer(RepoSearchResult.Error(exception))
-        }
-
-        isRequestInProgress = false
-        return successful
-    }
 
-    private fun reposByName(query: String): List<Repo> {
-        // from the in memory cache select only the repos whose name or description matches
-        // the query. Then order the results.
-        return inMemoryCache.filter {
-            it.name.contains(query, true) ||
-                    (it.description != null && it.description.contains(query, true))
-        }.sortedWith(compareByDescending<Repo> { it.stars }.thenBy { it.name })
+        return PagingDataFlow(
+                config = PagingConfig(pageSize = NETWORK_PAGE_SIZE),
+                pagingSourceFactory = { GithubPagingSource(service, query) }
+        )
     }
 
     companion object {

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

@@ -17,24 +17,24 @@
 package com.example.android.codelabs.paging.ui
 
 import android.view.ViewGroup
+import androidx.paging.PagingDataAdapter
 import androidx.recyclerview.widget.DiffUtil
-import androidx.recyclerview.widget.ListAdapter
+import androidx.recyclerview.widget.RecyclerView.ViewHolder
+import com.example.android.codelabs.paging.R
 import com.example.android.codelabs.paging.model.Repo
 
 /**
  * Adapter for the list of repositories.
  */
-class ReposAdapter : ListAdapter<Repo, androidx.recyclerview.widget.RecyclerView.ViewHolder>(REPO_COMPARATOR) {
+class ReposAdapter : PagingDataAdapter<Repo, ViewHolder>(REPO_COMPARATOR) {
 
-    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): androidx.recyclerview.widget.RecyclerView.ViewHolder {
+    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
         return RepoViewHolder.create(parent)
     }
 
-    override fun onBindViewHolder(holder: androidx.recyclerview.widget.RecyclerView.ViewHolder, position: Int) {
-        val repoItem = getItem(position)
-        if (repoItem != null) {
-            (holder as RepoViewHolder).bind(repoItem)
-        }
+    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
+        val repo = getItem(position)
+        (holder as RepoViewHolder).bind(repo)
     }
 
     companion object {

app/src/main/java/com/example/android/codelabs/paging/ui/ReposLoadStateAdapter.kt

@@ -13,56 +13,18 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 package com.example.android.codelabs.paging.ui
 
 import android.view.ViewGroup
-import androidx.recyclerview.widget.RecyclerView
-
-class ReposLoadStateAdapter(private val retry: () -> Unit) : RecyclerView.Adapter<ReposLoadStateViewHolder>() {
-
-    /**
-     * LoadState to present in the adapter.
-     *
-     * Changing this property will immediately notify the Adapter to change the item it's
-     * presenting.
-     */
-    var loadState: LoadState = LoadState.Done
-        set(loadState) {
-            if (field != loadState) {
-                val displayOldItem = displayLoadStateAsItem(field)
-                val displayNewItem = displayLoadStateAsItem(loadState)
-
-                if (displayOldItem && !displayNewItem) {
-                    notifyItemRemoved(0)
-                } else if (displayNewItem && !displayOldItem) {
-                    notifyItemInserted(0)
-                } else if (displayOldItem && displayNewItem) {
-                    notifyItemChanged(0)
-                }
-                field = loadState
-            }
-        }
+import androidx.paging.LoadState
+import androidx.paging.LoadStateAdapter
 
-    override fun onBindViewHolder(holder: ReposLoadStateViewHolder, position: Int) {
+class ReposLoadStateAdapter(private val retry: () -> Unit) : LoadStateAdapter<ReposLoadStateViewHolder>() {
+    override fun onBindViewHolder(holder: ReposLoadStateViewHolder, loadState: LoadState) {
         holder.bind(loadState)
     }
 
-    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ReposLoadStateViewHolder {
+    override fun onCreateViewHolder(parent: ViewGroup, loadState: LoadState): ReposLoadStateViewHolder {
         return ReposLoadStateViewHolder.create(parent, retry)
     }
-
-    override fun getItemViewType(position: Int): Int = 0
-
-    override fun getItemCount(): Int = if (displayLoadStateAsItem(loadState)) 1 else 0
-
-    /**
-     * Returns true if the LoadState should be displayed as a list item when active.
-     *
-     *  [LoadState.Loading] and [LoadState.Error] present as list items,
-     * [LoadState.Done] is not.
-     */
-    private fun displayLoadStateAsItem(loadState: LoadState): Boolean {
-        return loadState is LoadState.Loading || loadState is LoadState.Error
-    }
-}
+}

app/src/main/java/com/example/android/codelabs/paging/ui/ReposLoadStateViewHolder.kt

@@ -22,6 +22,7 @@ import android.view.ViewGroup
 import android.widget.Button
 import android.widget.ProgressBar
 import android.widget.TextView
+import androidx.paging.LoadState
 import androidx.recyclerview.widget.RecyclerView
 import com.example.android.codelabs.paging.R
 import com.example.android.codelabs.paging.databinding.ReposLoadStateHeaderViewItemBinding
@@ -60,4 +61,4 @@ class ReposLoadStateViewHolder(
             return ReposLoadStateViewHolder(binding, retry)
         }
     }
-}
+}