library: restore detail scroll positions after the rows load

The lazy list restores its saved position before a paging-backed playlist has replayed its cached pages, so a zero-item first frame clamped it back to the top. Track the position separately and reapply it once the item exists, which covers paged playlists as well as the album and artist lists. The test disposes and restores the scaffold with an empty first frame to keep this from regressing.
2026-11-15 00:42:54 +01:00 · 2026-10-21 10:13:52 +00:00
parent 0602f835dc
commit 61774a19ca
2 changed files with 116 additions and 1 deletions
@@ -0,0 +1,82 @@
+package com.subtracks.ui.components
+
+import androidx.activity.ComponentActivity
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.lazy.LazyListScope
+import androidx.compose.material3.Text
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableIntStateOf
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.saveable.rememberSaveableStateHolder
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.test.assertIsDisplayed
+import androidx.compose.ui.test.hasScrollAction
+import androidx.compose.ui.test.hasText
+import androidx.compose.ui.test.junit4.v2.createAndroidComposeRule
+import androidx.compose.ui.test.onNodeWithText
+import androidx.compose.ui.test.performScrollToNode
+import androidx.compose.ui.unit.dp
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.subtracks.ui.theme.SubtracksTheme
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.annotation.GraphicsMode
+
+@RunWith(AndroidJUnit4::class)
+@GraphicsMode(GraphicsMode.Mode.NATIVE)
+class HeroDetailScaffoldRestoreTest {
+    @get:Rule
+    val composeRule = createAndroidComposeRule<ComponentActivity>()
+
+    @Test
+    fun aRestoredScreenWaitsForItsRowsBeforeRestoringTheScrollPosition() {
+        var visible by mutableStateOf(true)
+        var rows by mutableIntStateOf(100)
+        composeRule.setContent {
+            SubtracksTheme {
+                val holder = rememberSaveableStateHolder()
+                if (visible) {
+                    holder.SaveableStateProvider("detail") {
+                        HeroDetailScaffold(
+                            artwork = null,
+                            title = "Album",
+                            onBack = {},
+                            header = { _, _ -> Box(Modifier.height(200.dp)) },
+                            content = { rowModifier -> rowItems(rows, rowModifier) },
+                        )
+                    }
+                }
+            }
+        }
+
+        composeRule.onNode(hasScrollAction()).performScrollToNode(hasText("Item 20"))
+        composeRule.onNodeWithText("Item 20").assertIsDisplayed()
+
+        composeRule.runOnIdle { visible = false }
+        composeRule.runOnIdle {
+            rows = 0
+            visible = true
+        }
+        composeRule.waitForIdle()
+        composeRule.runOnIdle { rows = 100 }
+        composeRule.waitForIdle()
+
+        composeRule.onNodeWithText("Item 20").assertIsDisplayed()
+    }
+
+    private fun LazyListScope.rowItems(
+        count: Int,
+        modifier: Modifier,
+    ) {
+        repeat(count) { index ->
+            item(key = index) {
+                Box(modifier.height(48.dp)) {
+                    Text("Item $index")
+                }
+            }
+        }
+    }
+}