Apply code cleanups from step13

app/build.gradle

@@ -62,8 +62,9 @@ dependencies {
     implementation "com.google.android.material:material:$materialVersion"
 
     // architecture components
+    implementation "androidx.core:core-ktx:$coreVersion"
     implementation "androidx.lifecycle:lifecycle-extensions:$lifecycleVersion"
-    implementation "androidx.lifecycle:lifecycle-runtime:$lifecycleVersion"
+    implementation "androidx.lifecycle:lifecycle-runtime-ktx:$lifecycleVersion"
     implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycleVersion"
     implementation "androidx.lifecycle:lifecycle-livedata-ktx:$lifecycleVersion"
     implementation "androidx.room:room-runtime:$roomVersion"

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

@@ -0,0 +1,50 @@
+/*
+ * 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 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
+
+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
+            LoadResult.Page(
+                    data = repos,
+                    prevKey = if (position == GITHUB_STARTING_PAGE_INDEX) null else position - 1,
+                    nextKey = if (repos.isEmpty()) null else position + 1
+            )
+        } catch (exception: IOException) {
+            LoadResult.Error(exception)
+        } catch (exception: HttpException) {
+            LoadResult.Error(exception)
+        }
+    }
+}

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

@@ -17,95 +17,28 @@
 package com.example.android.codelabs.paging.data
 
 import android.util.Log
+import androidx.paging.Pager
+import androidx.paging.PagingConfig
+import androidx.paging.PagingData
 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
-        inMemoryCache.clear()
-        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")
-            val repos = response.items ?: emptyList()
-            inMemoryCache.addAll(repos)
-            val reposByName = reposByName(query)
-            searchResults.offer(RepoSearchResult.Success(reposByName))
-            successful = true
-        } 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 Pager(
+                config = PagingConfig(pageSize = NETWORK_PAGE_SIZE),
+                pagingSourceFactory = { GithubPagingSource(service, query) }
+        ).flow
     }
 
     companion object {

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

@@ -17,20 +17,21 @@
 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.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) {
+    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
         val repoItem = getItem(position)
         if (repoItem != null) {
             (holder as RepoViewHolder).bind(repoItem)

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

@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2020 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.ui
+
+import android.view.ViewGroup
+import androidx.paging.LoadState
+import androidx.paging.LoadStateAdapter
+
+class ReposLoadStateAdapter(
+        private val retry: () -> Unit
+) : LoadStateAdapter<ReposLoadStateViewHolder>() {
+    override fun onBindViewHolder(holder: ReposLoadStateViewHolder, loadState: LoadState) {
+        holder.bind(loadState)
+    }
+
+    override fun onCreateViewHolder(parent: ViewGroup, loadState: LoadState): ReposLoadStateViewHolder {
+        return ReposLoadStateViewHolder.create(parent, retry)
+    }
+}

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

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2020 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.ui
+
+import android.view.LayoutInflater
+import android.view.ViewGroup
+import androidx.core.view.isVisible
+import androidx.paging.LoadState
+import androidx.recyclerview.widget.RecyclerView
+import com.example.android.codelabs.paging.R
+import com.example.android.codelabs.paging.databinding.ReposLoadStateFooterViewItemBinding
+
+class ReposLoadStateViewHolder(
+        private val binding: ReposLoadStateFooterViewItemBinding,
+        retry: () -> Unit
+) : RecyclerView.ViewHolder(binding.root) {
+
+    init {
+        binding.retryButton.setOnClickListener { retry.invoke() }
+    }
+
+    fun bind(loadState: LoadState) {
+        if (loadState is LoadState.Error) {
+            binding.errorMsg.text = loadState.error.localizedMessage
+        }
+        binding.progressBar.isVisible = loadState is LoadState.Loading
+        binding.retryButton.isVisible = loadState !is LoadState.Loading
+        binding.errorMsg.isVisible = loadState !is LoadState.Loading
+    }
+
+    companion object {
+        fun create(parent: ViewGroup, retry: () -> Unit): ReposLoadStateViewHolder {
+            val view = LayoutInflater.from(parent.context)
+                    .inflate(R.layout.repos_load_state_footer_view_item, parent, false)
+            val binding = ReposLoadStateFooterViewItemBinding.bind(view)
+            return ReposLoadStateViewHolder(binding, retry)
+        }
+    }
+}