Fix predictive back crash after launch page change

https://issuetracker.google.com/384186542

app/src/main/kotlin/com/hippo/ehviewer/Settings.kt

@@ -107,6 +107,7 @@ object Settings : DataStorePreferences(null) {
     var favCloudCount by intPref("fav_cloud", 0).emitTo(_favFlow)
 
     val gallerySite = intPref("gallery_site_2", 0).observed { updateWhenGallerySiteChanges() }
+    val launchPage = intPref("launch_page_2", 0)
     val listMode = intPref("list_mode_2", 0)
     val detailSize = intPref("detail_size_2", 0)
     val thumbColumns = intPref("thumb_columns", 3)
@@ -145,7 +146,6 @@ object Settings : DataStorePreferences(null) {
     var timeoutSpeed by intPref("timeout_speed_level", 6)
     var theme by intPref("theme_2", -1).observed { updateWhenThemeChanges() }
     var readCacheSize by intPref("read_cache_size_2", 640)
-    var launchPage by intPref("launch_page_2", 0)
     var commentThreshold by intPref("comment_threshold", -100)
     var hardwareBitmapThreshold by intPref("hardware_bitmap_threshold", 16384)
     var showComments by boolPref("show_gallery_comments", true)

app/src/main/kotlin/com/hippo/ehviewer/ui/MainActivity.kt

@@ -173,9 +173,6 @@ private val navItems = arrayOf<Triple<Direction, Int, ImageVector>>(
     Triple(SettingsScreenDestination, R.string.settings, Icons.Default.Settings),
 )
 
-val StartDestination
-    get() = navItems[Settings.launchPage].first
-
 class MainActivity : EhActivity() {
 
     private var shareUrl: String? = null
@@ -359,6 +356,7 @@ class MainActivity : EhActivity() {
             val density = LocalDensity.current
             val adaptiveInfo = currentWindowAdaptiveInfo()
             val needSignIn by Settings.needSignIn.collectAsState()
+            val launchPage by Settings.launchPage.collectAsState()
             CompositionLocalProvider(
                 LocalNavDrawerState provides navDrawerState,
                 LocalSideSheetState provides sideSheetState,
@@ -443,7 +441,7 @@ class MainActivity : EhActivity() {
                                 CompositionLocalProvider(LocalSharedTransitionScope provides this) {
                                     val start = when {
                                         needSignIn -> SignInScreenDestination
-                                        hasNetwork -> StartDestination
+                                        hasNetwork -> navItems[launchPage].first
                                         else -> DownloadsScreenDestination
                                     }
                                     DestinationsNavHost(

app/src/main/kotlin/com/hippo/ehviewer/ui/settings/EhScreen.kt

@@ -187,7 +187,7 @@ fun AnimatedVisibilityScope.EhScreen(navigator: DestinationsNavigator) = Screen(
                 title = stringResource(id = R.string.settings_eh_launch_page),
                 entry = R.array.launch_page_entries,
                 entryValueRes = R.array.launch_page_entry_values,
-                value = Settings::launchPage.observed,
+                value = Settings.launchPage.asMutableState(),
             )
             val listMode = Settings.listMode.asMutableState()
             SimpleMenuPreferenceInt(