From c160d18ea505969674ae7b9b8bfa31b6c949fdd9 Mon Sep 17 00:00:00 2001
From: Noah Statton <nwstatton@gmail.com>
Date: Fri, 15 May 2026 14:55:17 -0400
Subject: [PATCH] fix: render error UI for TopicUiState.Error instead of
 crashing

---
 .../topic/api/src/main/res/values/strings.xml |  1 +
 .../feature/topic/impl/TopicScreenTest.kt     | 22 +++++++++++++++++++
 .../feature/topic/impl/TopicScreen.kt         | 22 +++++++++++++++++--
 3 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/feature/topic/api/src/main/res/values/strings.xml b/feature/topic/api/src/main/res/values/strings.xml
index 1e3f376cf8..a629d0aade 100644
--- a/feature/topic/api/src/main/res/values/strings.xml
+++ b/feature/topic/api/src/main/res/values/strings.xml
@@ -16,4 +16,5 @@
 -->
 <resources>
     <string name="feature_topic_api_loading">Loading topic</string>
+    <string name="feature_topic_api_error_header">Couldn\'t load topic</string>
 </resources>
diff --git a/feature/topic/impl/src/androidTest/kotlin/com/google/samples/apps/nowinandroid/feature/topic/impl/TopicScreenTest.kt b/feature/topic/impl/src/androidTest/kotlin/com/google/samples/apps/nowinandroid/feature/topic/impl/TopicScreenTest.kt
index 5f6782160a..57c5682f7b 100644
--- a/feature/topic/impl/src/androidTest/kotlin/com/google/samples/apps/nowinandroid/feature/topic/impl/TopicScreenTest.kt
+++ b/feature/topic/impl/src/androidTest/kotlin/com/google/samples/apps/nowinandroid/feature/topic/impl/TopicScreenTest.kt
@@ -42,11 +42,13 @@ class TopicScreenTest {
     val composeTestRule = createAndroidComposeRule<ComponentActivity>()
 
     private lateinit var topicLoading: String
+    private lateinit var topicErrorHeader: String
 
     @Before
     fun setup() {
         composeTestRule.activity.apply {
             topicLoading = getString(R.string.feature_topic_api_loading)
+            topicErrorHeader = getString(R.string.feature_topic_api_error_header)
         }
     }
 
@@ -97,6 +99,26 @@ class TopicScreenTest {
             .assertExists()
     }
 
+    @Test
+    fun errorMessage_whenTopicIsError_isShown() {
+        composeTestRule.setContent {
+            TopicScreen(
+                topicUiState = TopicUiState.Error,
+                newsUiState = NewsUiState.Loading,
+                showBackButton = true,
+                onBackClick = {},
+                onFollowClick = {},
+                onTopicClick = {},
+                onBookmarkChanged = { _, _ -> },
+                onNewsResourceViewed = {},
+            )
+        }
+
+        composeTestRule
+            .onNodeWithText(topicErrorHeader)
+            .assertExists()
+    }
+
     @Test
     fun news_whenTopicIsLoading_isNotShown() {
         composeTestRule.setContent {
diff --git a/feature/topic/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/topic/impl/TopicScreen.kt b/feature/topic/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/topic/impl/TopicScreen.kt
index 5c802f225b..7a78c625ef 100644
--- a/feature/topic/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/topic/impl/TopicScreen.kt
+++ b/feature/topic/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/topic/impl/TopicScreen.kt
@@ -129,7 +129,9 @@ internal fun TopicScreen(
                     )
                 }
 
-                TopicUiState.Error -> TODO()
+                TopicUiState.Error -> item {
+                    TopicErrorBody()
+                }
                 is TopicUiState.Success -> {
                     item {
                         TopicToolbar(
@@ -177,7 +179,7 @@ private fun topicItemsSize(
     topicUiState: TopicUiState,
     newsUiState: NewsUiState,
 ) = when (topicUiState) {
-    TopicUiState.Error -> 0 // Nothing
+    TopicUiState.Error -> 1 // Error message
     TopicUiState.Loading -> 1 // Loading bar
     is TopicUiState.Success -> when (newsUiState) {
         NewsUiState.Error -> 0 // Nothing
@@ -203,6 +205,22 @@ private fun LazyListScope.topicBody(
     userNewsResourceCards(news, onBookmarkChanged, onNewsResourceViewed, onTopicClick)
 }
 
+@Composable
+private fun TopicErrorBody() {
+    Column(
+        horizontalAlignment = Alignment.CenterHorizontally,
+        modifier = Modifier
+            .fillMaxWidth()
+            .padding(horizontal = 48.dp),
+    ) {
+        Text(
+            text = stringResource(id = TopicR.string.feature_topic_api_error_header),
+            style = MaterialTheme.typography.bodyLarge,
+            modifier = Modifier.padding(vertical = 24.dp),
+        )
+    }
+}
+
 @Composable
 private fun TopicHeader(name: String, description: String, imageUrl: String) {
     Column(