Add jetpack support(androidx) to [Solution]

app/build.gradle

@@ -20,6 +20,10 @@ apply plugin: 'kotlin-kapt'
 apply plugin: 'kotlin-android-extensions'
 
 android {
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
     compileSdkVersion rootProject.compileSdkVersion
     defaultConfig {
         applicationId "com.example.android.codelabs.paging"
@@ -39,18 +43,17 @@ android {
 
 dependencies {
     implementation fileTree(dir: 'libs', include: ['*.jar'])
-    implementation"org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
-    implementation "com.android.support:appcompat-v7:$supportLibVersion"
-    implementation "com.android.support.constraint:constraint-layout:$constraintLayoutVersion"
-    implementation "com.android.support:design:$supportLibVersion"
+    implementation"org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
+    implementation "androidx.appcompat:appcompat:$appCompat"
+    implementation "androidx.constraintlayout:constraintlayout:$constraintLayoutVersion"
+    implementation "com.google.android.material:material:$design"
 
     // architecture components
-    implementation "android.arch.lifecycle:extensions:$archComponentsVersion"
-    implementation "android.arch.lifecycle:runtime:$archComponentsVersion"
-    implementation "android.arch.persistence.room:runtime:$roomVersion"
-    implementation "android.arch.paging:runtime:$pagingVersion"
-    kapt "android.arch.lifecycle:compiler:$archComponentsVersion"
-    kapt "android.arch.persistence.room:compiler:$roomVersion"
+    implementation "androidx.paging:paging-runtime:$pagingVersion"
+    kapt "androidx.room:room-compiler:$roomVersion"
+    implementation "androidx.room:room-runtime:$roomVersion"
+    implementation "androidx.lifecycle:lifecycle-extensions:$archComponentsVersion"
+    implementation "androidx.lifecycle:lifecycle-common-java8:$archComponentsVersion"
 
     // retrofit
     implementation "com.squareup.retrofit2:retrofit:$retrofitVersion"
@@ -60,6 +63,6 @@ dependencies {
 
     // testing
     testImplementation "junit:junit:$junitVersion"
-    androidTestImplementation "com.android.support.test:runner:$runnerVersion"
-    androidTestImplementation "com.android.support.test.espresso:espresso-core:$espressoVersion"
+    androidTestImplementation "androidx.test:runner:$runnerVersion"
+    androidTestImplementation "androidx.test.espresso:espresso-core:$espressoVersion"
 }

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

@@ -16,8 +16,8 @@
 
 package com.example.android.codelabs.paging
 
-import android.arch.lifecycle.ViewModelProvider
 import android.content.Context
+import androidx.lifecycle.ViewModelProvider
 import com.example.android.codelabs.paging.api.GithubService
 import com.example.android.codelabs.paging.data.GithubRepository
 import com.example.android.codelabs.paging.db.GithubLocalCache

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

@@ -16,10 +16,9 @@
 
 package com.example.android.codelabs.paging.data
 
-import android.arch.lifecycle.MutableLiveData
 import android.util.Log
+import androidx.paging.LivePagedListBuilder
 import com.example.android.codelabs.paging.api.GithubService
-import com.example.android.codelabs.paging.api.searchRepos
 import com.example.android.codelabs.paging.db.GithubLocalCache
 import com.example.android.codelabs.paging.model.RepoSearchResult
 
@@ -31,49 +30,31 @@ class GithubRepository(
         private val cache: GithubLocalCache
 ) {
 
-    // keep the last requested page. When the request is successful, increment the page number.
-    private var lastRequestedPage = 1
-
-    // LiveData of network errors.
-    private val networkErrors = MutableLiveData<String>()
-
-    // avoid triggering multiple requests in the same time
-    private var isRequestInProgress = false
-
     /**
      * Search repositories whose names match the query.
      */
     fun search(query: String): RepoSearchResult {
         Log.d("GithubRepository", "New query: $query")
-        lastRequestedPage = 1
-        requestAndSaveData(query)
-
-        // Get data from the local cache
-        val data = cache.reposByName(query)
 
-        return RepoSearchResult(data, networkErrors)
-    }
+        // Get data source factory from the local cache
+        val dataSourceFactory = cache.reposByName(query)
 
-    fun requestMore(query: String) {
-        requestAndSaveData(query)
-    }
+        // every new query creates a new BoundaryCallback
+        // The BoundaryCallback will observe when the user reaches to the edges of
+        // the list and update the database with extra data
+        val boundaryCallback = RepoBoundaryCallback(query, service, cache)
+        val networkErrors = boundaryCallback.networkErrors
 
-    private fun requestAndSaveData(query: String) {
-        if (isRequestInProgress) return
+        // Get the paged list
+        val data = LivePagedListBuilder(dataSourceFactory, DATABASE_PAGE_SIZE)
+                .setBoundaryCallback(boundaryCallback)
+                .build()
 
-        isRequestInProgress = true
-        searchRepos(service, query, lastRequestedPage, NETWORK_PAGE_SIZE, { repos ->
-            cache.insert(repos, {
-                lastRequestedPage++
-                isRequestInProgress = false
-            })
-        }, { error ->
-            networkErrors.postValue(error)
-            isRequestInProgress = false
-        })
+        // Get the network errors exposed by the boundary callback
+        return RepoSearchResult(data, networkErrors)
     }
 
     companion object {
-        private const val NETWORK_PAGE_SIZE = 50
+        private const val DATABASE_PAGE_SIZE = 20
     }
 }

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

@@ -0,0 +1,83 @@
+/*
+ * 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 android.util.Log
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.MutableLiveData
+import androidx.paging.PagedList
+import com.example.android.codelabs.paging.api.GithubService
+import com.example.android.codelabs.paging.api.searchRepos
+import com.example.android.codelabs.paging.db.GithubLocalCache
+import com.example.android.codelabs.paging.model.Repo
+
+/**
+ * This boundary callback gets notified when user reaches to the edges of the list for example when
+ * the database cannot provide any more data.
+ **/
+class RepoBoundaryCallback(
+        private val query: String,
+        private val service: GithubService,
+        private val cache: GithubLocalCache
+) : PagedList.BoundaryCallback<Repo>() {
+
+    companion object {
+        private const val NETWORK_PAGE_SIZE = 50
+    }
+
+    // keep the last requested page. When the request is successful, increment the page number.
+    private var lastRequestedPage = 1
+
+    private val _networkErrors = MutableLiveData<String>()
+    // LiveData of network errors.
+    val networkErrors: LiveData<String>
+        get() = _networkErrors
+
+    // avoid triggering multiple requests in the same time
+    private var isRequestInProgress = false
+
+    /**
+     * Database returned 0 items. We should query the backend for more items.
+     */
+    override fun onZeroItemsLoaded() {
+        Log.d("RepoBoundaryCallback", "onZeroItemsLoaded")
+        requestAndSaveData(query)
+    }
+
+    /**
+     * When all items in the database were loaded, we need to query the backend for more items.
+     */
+    override fun onItemAtEndLoaded(itemAtEnd: Repo) {
+        Log.d("RepoBoundaryCallback", "onItemAtEndLoaded")
+        requestAndSaveData(query)
+    }
+
+    private fun requestAndSaveData(query: String) {
+        if (isRequestInProgress) return
+
+        isRequestInProgress = true
+        searchRepos(service, query, lastRequestedPage, NETWORK_PAGE_SIZE, { repos ->
+            cache.insert(repos, {
+                lastRequestedPage++
+                isRequestInProgress = false
+            })
+        }, { error ->
+            _networkErrors.postValue(error)
+            isRequestInProgress = false
+        })
+    }
+}

app/src/main/java/com/example/android/codelabs/paging/db/GithubLocalCache.kt

@@ -16,9 +16,8 @@
 
 package com.example.android.codelabs.paging.db
 
-import android.arch.lifecycle.LiveData
-import android.arch.paging.DataSource
 import android.util.Log
+import androidx.paging.DataSource
 import com.example.android.codelabs.paging.model.Repo
 import java.util.concurrent.Executor
 
@@ -34,7 +33,7 @@ class GithubLocalCache(
     /**
      * Insert a list of repos in the database, on a background thread.
      */
-    fun insert(repos: List<Repo>, insertFinished: ()-> Unit) {
+    fun insert(repos: List<Repo>, insertFinished: () -> Unit) {
         ioExecutor.execute {
             Log.d("GithubLocalCache", "inserting ${repos.size} repos")
             repoDao.insert(repos)
@@ -48,7 +47,7 @@ class GithubLocalCache(
      * any characters between the words.
      * @param name repository name
      */
-    fun reposByName(name: String): LiveData<List<Repo>> {
+    fun reposByName(name: String): DataSource.Factory<Int, Repo> {
         // appending '%' so we can allow other characters to be before and after the query string
         val query = "%${name.replace(' ', '%')}%"
         return repoDao.reposByName(query)

app/src/main/java/com/example/android/codelabs/paging/db/RepoDao.kt

@@ -16,11 +16,11 @@
 
 package com.example.android.codelabs.paging.db
 
-import android.arch.lifecycle.LiveData
-import android.arch.persistence.room.Dao
-import android.arch.persistence.room.Insert
-import android.arch.persistence.room.OnConflictStrategy
-import android.arch.persistence.room.Query
+import androidx.paging.DataSource
+import androidx.room.Dao
+import androidx.room.Insert
+import androidx.room.OnConflictStrategy
+import androidx.room.Query
 import com.example.android.codelabs.paging.model.Repo
 
 /**
@@ -37,6 +37,6 @@ interface RepoDao {
     // and order those results descending, by the number of stars and then by name
     @Query("SELECT * FROM repos WHERE (name LIKE :queryString) OR (description LIKE " +
             ":queryString) ORDER BY stars DESC, name ASC")
-    fun reposByName(queryString: String): LiveData<List<Repo>>
+    fun reposByName(queryString: String): DataSource.Factory<Int, Repo>
 
 }

app/src/main/java/com/example/android/codelabs/paging/db/RepoDatabase.kt

@@ -16,10 +16,10 @@
 
 package com.example.android.codelabs.paging.db
 
-import android.arch.persistence.room.Database
-import android.arch.persistence.room.Room
-import android.arch.persistence.room.RoomDatabase
 import android.content.Context
+import androidx.room.Database
+import androidx.room.Room
+import androidx.room.RoomDatabase
 import com.example.android.codelabs.paging.model.Repo
 
 /**

app/src/main/java/com/example/android/codelabs/paging/model/Repo.kt

@@ -16,8 +16,8 @@
 
 package com.example.android.codelabs.paging.model
 
-import android.arch.persistence.room.Entity
-import android.arch.persistence.room.PrimaryKey
+import androidx.room.Entity
+import androidx.room.PrimaryKey
 import com.google.gson.annotations.SerializedName
 
 /**

app/src/main/java/com/example/android/codelabs/paging/model/RepoSearchResult.kt

@@ -16,13 +16,14 @@
 
 package com.example.android.codelabs.paging.model
 
-import android.arch.lifecycle.LiveData
+import androidx.lifecycle.LiveData
+import androidx.paging.PagedList
 
 /**
  * RepoSearchResult from a search, which contains LiveData<List<Repo>> holding query data,
  * and a LiveData<String> of network error state.
  */
 data class RepoSearchResult(
-        val data: LiveData<List<Repo>>,
+        val data: LiveData<PagedList<Repo>>,
         val networkErrors: LiveData<String>
 )

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

@@ -18,11 +18,11 @@ package com.example.android.codelabs.paging.ui
 
 import android.content.Intent
 import android.net.Uri
-import android.support.v7.widget.RecyclerView
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
 import android.widget.TextView
+import androidx.recyclerview.widget.RecyclerView
 import com.example.android.codelabs.paging.R
 import com.example.android.codelabs.paging.model.Repo
 

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

@@ -16,16 +16,16 @@
 
 package com.example.android.codelabs.paging.ui
 
-import android.support.v7.recyclerview.extensions.ListAdapter
-import android.support.v7.util.DiffUtil
-import android.support.v7.widget.RecyclerView
 import android.view.ViewGroup
+import androidx.paging.PagedListAdapter
+import androidx.recyclerview.widget.DiffUtil
+import androidx.recyclerview.widget.RecyclerView
 import com.example.android.codelabs.paging.model.Repo
 
 /**
  * Adapter for the list of repositories.
  */
-class ReposAdapter : ListAdapter<Repo, RecyclerView.ViewHolder>(REPO_COMPARATOR) {
+class ReposAdapter : PagedListAdapter<Repo, RecyclerView.ViewHolder>(REPO_COMPARATOR) {
 
     override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
         return RepoViewHolder.create(parent)