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fix: render error UI for TopicUiState.Error instead of crashing #2109

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fix: render error UI for TopicUiState.Error instead of crashing #2109

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1 change: 1 addition & 0 deletions feature/topic/api/src/main/res/values/strings.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -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>
22 changes: 22 additions & 0 deletions ...oidTest/kotlin/com/google/samples/apps/nowinandroid/feature/topic/impl/TopicScreenTest.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -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)
}
}

Expand Down Expand Up @@ -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 {
Expand Down
22 changes: 20 additions & 2 deletions ...pl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/topic/impl/TopicScreen.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -129,7 +129,9 @@ internal fun TopicScreen(
)
}

TopicUiState.Error -> TODO()
TopicUiState.Error -> item {
TopicErrorBody()
}
is TopicUiState.Success -> {
item {
TopicToolbar(
Expand Down Expand Up @@ -177,7 +179,7 @@ private fun topicItemsSize(
topicUiState: TopicUiState,
newsUiState: NewsUiState,
) = when (topicUiState) {
TopicUiState.Error -> 0 // Nothing
TopicUiState.Error -> 1 // Error message
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@gemini-code-assist gemini-code-assist Bot May 15, 2026

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medium

While updating this to 1 is correct for the new error state, the existing logic for TopicUiState.Success (lines 185-186) appears to be incorrect as it doesn't account for the Toolbar and Header items which are always rendered in that state. This discrepancy will cause the scrollbar to be incorrectly sized or hidden when news is loading or has an error. Consider updating the entire function to ensure the scrollbar accurately reflects the number of items in the LazyColumn.

TopicUiState.Loading -> 1 // Loading bar
is TopicUiState.Success -> when (newsUiState) {
NewsUiState.Error -> 0 // Nothing
Expand All @@ -203,6 +205,22 @@ private fun LazyListScope.topicBody(
userNewsResourceCards(news, onBookmarkChanged, onNewsResourceViewed, onTopicClick)
}

@Composable
private fun TopicErrorBody() {
Column(
horizontalAlignment = Alignment.CenterHorizontally,
modifier = Modifier
Comment on lines +209 to +212
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@gemini-code-assist gemini-code-assist Bot May 15, 2026

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medium

It is a best practice in Compose to have a modifier parameter for all composables to allow for layout adjustments from the caller. This also ensures that the internal Column uses the passed-in modifier as its base.

Suggested change
private fun TopicErrorBody() {
Column(
horizontalAlignment = Alignment.CenterHorizontally,
modifier = Modifier
private fun TopicErrorBody(modifier: Modifier = Modifier) {
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(
Expand Down