Adding header/footer that shows loading progress and error status

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

@@ -36,17 +36,21 @@ class GithubPagingSource(
     override suspend fun load(params: LoadParams<Int>): LoadResult<Int, Repo> {
         val position = params.key ?: GITHUB_STARTING_PAGE_INDEX
         val apiQuery = query + IN_QUALIFIER
-        val apiResponse = service.searchRepos(apiQuery, position, GithubRepository.NETWORK_PAGE_SIZE)
-        return if (apiResponse.isSuccessful) {
-            val repos = apiResponse.body()?.items ?: emptyList()
-            LoadResult.Page(
-                    data = repos,
-                    prevKey = if (position == GITHUB_STARTING_PAGE_INDEX) null else -1,
-                    // if we don't get any results, we consider that we're at the last page
-                    nextKey = if (repos.isEmpty()) null else position + 1
-            )
-        } else {
-            LoadResult.Error(IOException(apiResponse.message()))
+        try {
+            val apiResponse = service.searchRepos(apiQuery, position, GithubRepository.NETWORK_PAGE_SIZE)
+            return if (apiResponse.isSuccessful) {
+                val repos = apiResponse.body()?.items ?: emptyList()
+                LoadResult.Page(
+                        data = repos,
+                        prevKey = if (position == GITHUB_STARTING_PAGE_INDEX) null else -1,
+                        // if we don't get any results, we consider that we're at the last page
+                        nextKey = if (repos.isEmpty()) null else position + 1
+                )
+            } else {
+                LoadResult.Error(IOException(apiResponse.message()))
+            }
+        } catch (exception: Exception) {
+            return LoadResult.Error(exception)
         }
     }
 }

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

@@ -0,0 +1,32 @@
+package com.example.android.codelabs.paging.ui
+
+/*
+ * 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.
+ */
+
+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(retry, parent)
+    }
+
+}

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

@@ -0,0 +1,61 @@
+package com.example.android.codelabs.paging.ui
+
+/*
+ * 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.
+ */
+
+import android.view.LayoutInflater
+import android.view.View
+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
+
+class ReposLoadStateViewHolder(
+        retry: () -> Unit,
+        view: View
+) : RecyclerView.ViewHolder(view) {
+    private val progressBar: ProgressBar = itemView.findViewById(R.id.progress_bar)
+    private val errorMsg: TextView = itemView.findViewById(R.id.error_msg)
+    private val retry: Button = itemView.findViewById<Button>(R.id.retry_button).also {
+        it.setOnClickListener { retry.invoke() }
+    }
+
+    fun bind(loadState: LoadState) {
+        if (loadState is LoadState.Error) {
+            errorMsg.text = loadState.error.localizedMessage
+        }
+        progressBar.visibility = toVisibility(loadState == LoadState.Loading)
+        retry.visibility = toVisibility(loadState != LoadState.Loading)
+        errorMsg.visibility = toVisibility(loadState != LoadState.Loading)
+    }
+
+    private fun toVisibility(constraint: Boolean): Int = if (constraint) {
+        View.VISIBLE
+    } else {
+        View.GONE
+    }
+
+    companion object {
+        fun create(retry: () -> Unit, parent: ViewGroup): ReposLoadStateViewHolder {
+            val view = LayoutInflater.from(parent.context)
+                    .inflate(R.layout.repos_load_state_header_view_item, parent, false)
+            return ReposLoadStateViewHolder(retry, view)
+        }
+    }
+}

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

@@ -26,6 +26,7 @@ import androidx.appcompat.app.AppCompatActivity
 import androidx.lifecycle.ViewModelProvider
 import androidx.lifecycle.lifecycleScope
 import androidx.paging.LoadState
+import androidx.paging.LoadType
 import androidx.recyclerview.widget.DividerItemDecoration
 import com.example.android.codelabs.paging.Injection
 import com.example.android.codelabs.paging.databinding.ActivitySearchRepositoriesBinding
@@ -58,9 +59,21 @@ class SearchRepositoriesActivity : AppCompatActivity() {
         val decoration = DividerItemDecoration(this, DividerItemDecoration.VERTICAL)
         binding.list.addItemDecoration(decoration)
 
-        binding.list.adapter = adapter
+        binding.list.adapter = adapter.withLoadStateHeaderAndFooter(
+                header = ReposLoadStateAdapter { adapter.retry() },
+                footer = ReposLoadStateAdapter { adapter.retry() }
+        )
         adapter.addLoadStateListener { loadType, loadState ->
             Log.d("SearchRepositoriesActivity", "adapter load: type = $loadType state = $loadState")
+            if (loadType == LoadType.REFRESH) {
+                binding.list.visibility = View.GONE
+                binding.progressBar.visibility = toVisibility(loadState == LoadState.Loading)
+                binding.retryButton.visibility = toVisibility(loadState is LoadState.Error)
+            } else {
+                binding.list.visibility = View.VISIBLE
+                binding.progressBar.visibility = View.GONE
+                binding.retryButton.visibility = View.GONE
+            }
             if (loadState is LoadState.Error) {
                 Toast.makeText(
                         this,
@@ -72,6 +85,7 @@ class SearchRepositoriesActivity : AppCompatActivity() {
         val query = savedInstanceState?.getString(LAST_SEARCH_QUERY) ?: DEFAULT_QUERY
         search(query)
         initSearch(query)
+        binding.retryButton.setOnClickListener { adapter.retry() }
     }
 
     override fun onSaveInstanceState(outState: Bundle) {
@@ -105,9 +119,6 @@ class SearchRepositoriesActivity : AppCompatActivity() {
             if (it.isNotEmpty()) {
                 binding.list.scrollToPosition(0)
                 search(it.toString())
-                // TODO how to clear the list
-                //  might not need it because of how Paging works
-//                adapter.collectFrom(PagingData.empty())
             }
         }
     }
@@ -123,14 +134,10 @@ class SearchRepositoriesActivity : AppCompatActivity() {
         }
     }
 
-    private fun showEmptyList(show: Boolean) {
-        if (show) {
-            binding.emptyList.visibility = View.VISIBLE
-            binding.list.visibility = View.GONE
-        } else {
-            binding.emptyList.visibility = View.GONE
-            binding.list.visibility = View.VISIBLE
-        }
+    private fun toVisibility(constraint: Boolean): Int = if (constraint) {
+        View.VISIBLE
+    } else {
+        View.GONE
     }
 
     companion object {

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

@@ -59,16 +59,25 @@
         app:layout_constraintTop_toBottomOf="@+id/input_layout"
         tools:ignore="UnusedAttribute"/>
 
-    <TextView android:id="@+id/emptyList"
-              android:layout_width="0dp"
-              android:layout_height="match_parent"
-              android:gravity="center"
-              android:text="@string/no_results"
-              android:textSize="@dimen/repo_name_size"
-              android:visibility="gone"
-              app:layout_constraintBottom_toBottomOf="parent"
-              app:layout_constraintEnd_toEndOf="parent"
-              app:layout_constraintStart_toStartOf="parent"
-              app:layout_constraintTop_toTopOf="parent"/>
+    <ProgressBar
+        android:id="@+id/progress_bar"
+        style="?android:attr/progressBarStyle"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:layout_gravity="center"
+        app:layout_constraintLeft_toLeftOf="parent"
+        app:layout_constraintRight_toRightOf="parent"
+        app:layout_constraintTop_toTopOf="parent"
+        app:layout_constraintBottom_toBottomOf="parent"/>
+
+    <Button
+        android:id="@+id/retry_button"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="@string/retry"
+        app:layout_constraintLeft_toLeftOf="parent"
+        app:layout_constraintRight_toRightOf="parent"
+        app:layout_constraintTop_toTopOf="parent"
+        app:layout_constraintBottom_toBottomOf="parent"/>
 
 </androidx.constraintlayout.widget.ConstraintLayout>

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

@@ -0,0 +1,42 @@
+<?xml version="1.0" encoding="utf-8"?><!--
+  ~ 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.
+  -->
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:orientation="vertical"
+    android:padding="8dp">
+    <TextView
+        android:id="@+id/error_msg"
+        android:textColor="?android:textColorPrimary"
+        android:textSize="@dimen/error_text_size"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_gravity="center_horizontal"
+        tools:text="Timeout"/>
+    <ProgressBar
+        android:id="@+id/progress_bar"
+        style="?android:attr/progressBarStyle"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:layout_gravity="center"/>
+    <Button
+        android:id="@+id/retry_button"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_gravity="center"
+        android:text="@string/retry"/>
+</LinearLayout>

app/src/main/res/values/dimens.xml

@@ -23,4 +23,5 @@
     <dimen name="repo_icon_size">24dp</dimen>
     <dimen name="loading_progress_bar_size">36dp</dimen>
     <dimen name="placeholder_item_height">32dp</dimen>
+    <dimen name="error_text_size">24sp</dimen>
 </resources>

app/src/main/res/values/strings.xml

@@ -21,4 +21,5 @@
     <string name="search_hint">GitHub Repository</string>
     <string name="no_results">No results 😓</string>
     <string name="unknown">\?</string>
+    <string name="retry">Retry</string>
 </resources>