Fix navigation: Splash never in backStack, BackHandler in ContentView, immersive mode reapplied on focus

Author: GreenGo Build

app/src/main/java/com/greengo/app/MainActivity.kt

@@ -2,8 +2,8 @@ package com.greengo.app
 
 import android.os.Bundle
 import androidx.activity.ComponentActivity
-import androidx.activity.OnBackPressedCallback
 import androidx.activity.compose.setContent
+import androidx.activity.enableEdgeToEdge
 import androidx.activity.viewModels
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.darkColorScheme
@@ -15,6 +15,7 @@ import androidx.core.view.WindowInsetsCompat
 import androidx.core.view.WindowInsetsControllerCompat
 import com.greengo.app.data.AppStateViewModel
 import com.greengo.app.data.AppTheme
+import com.greengo.app.data.Screen
 import com.greengo.app.ui.ContentView
 
 class MainActivity : ComponentActivity() {
@@ -24,27 +25,10 @@ class MainActivity : ComponentActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
 
-        // Let Compose draw under system bars (edge‑to‑edge)
+        // Edge-to-edge: Compose draws under system bars
         WindowCompat.setDecorFitsSystemWindows(window, false)
+        hideSystemBars()
 
-        // Hide both status and nav bars (immersive experience)
-        val insetsController = WindowInsetsControllerCompat(window, window.decorView)
-        insetsController.hide(WindowInsetsCompat.Type.systemBars())
-        insetsController.systemBarsBehavior =
-            WindowInsetsControllerCompat.BEHAVIOR_SHOW_TRANSIENT_BARS_BY_SWIPE
-
-        // Back button logic: internal navigation or exit
-        onBackPressedDispatcher.addCallback(this, object : OnBackPressedCallback(true) {
-            override fun handleOnBackPressed() {
-                if (vm.canNavigateBack()) {
-                    vm.navigateBack()
-                } else {
-                    finishAffinity()  // exit app
-                }
-            }
-        })
-
-        // Init your ViewModel state
         vm.init(applicationContext)
 
         setContent {
@@ -57,4 +41,22 @@ class MainActivity : ComponentActivity() {
             }
         }
     }
-}
+
+    override fun onWindowFocusChanged(hasFocus: Boolean) {
+        super.onWindowFocusChanged(hasFocus)
+        // Re-apply immersive mode whenever the window regains focus
+        // (system can restore bars after dialogs, notifications, etc.)
+        if (hasFocus) hideSystemBars()
+    }
+
+    private fun hideSystemBars() {
+        WindowInsetsControllerCompat(window, window.decorView).apply {
+            hide(WindowInsetsCompat.Type.systemBars())
+            systemBarsBehavior =
+                WindowInsetsControllerCompat.BEHAVIOR_SHOW_TRANSIENT_BARS_BY_SWIPE
+        }
+    }
+
+    // Back press is handled entirely by the ViewModel — no override needed here.
+    // ContentView / each screen handles BackHandler composable where appropriate.
+}

app/src/main/java/com/greengo/app/data/AppStateViewModel.kt

@@ -14,36 +14,46 @@ class AppStateViewModel : ViewModel() {
 
     fun init(context: Context) {
         prefs = context.getSharedPreferences("greengo_prefs", Context.MODE_PRIVATE)
-        _theme.value        = AppTheme.fromRawValue(prefs.getString("appTheme", "mint") ?: "mint")
-        _triviaScore.value  = prefs.getInt("score_trivia", 0)
-        _memoryScore.value  = prefs.getInt("score_memory", 0)
-        _oceanScore.value   = prefs.getInt("score_ocean", 0)
-        _skipMapInfo.value  = prefs.getBoolean("skip_mapInfo", false)
+        _theme.value         = AppTheme.fromRawValue(prefs.getString("appTheme", "mint") ?: "mint")
+        _triviaScore.value   = prefs.getInt("score_trivia", 0)
+        _memoryScore.value   = prefs.getInt("score_memory", 0)
+        _oceanScore.value    = prefs.getInt("score_ocean", 0)
+        _skipMapInfo.value   = prefs.getBoolean("skip_mapInfo", false)
         _skipOceanInfo.value = prefs.getBoolean("skip_oceanInfo", false)
-        _skipMemoryInfo.value = prefs.getBoolean("skip_memoryInfo", false)
+        _skipMemoryInfo.value= prefs.getBoolean("skip_memoryInfo", false)
     }
 
     // ── Navigation ────────────────────────────────────────────────────────────
+    // Rules:
+    //   • Splash is NEVER added to the back stack — it's a one-way gate.
+    //   • Home is the root. Back from Home exits the app.
+    //   • All other screens push to the stack normally.
 
     private val _screen = MutableStateFlow<Screen>(Screen.Splash)
     val screen: StateFlow<Screen> = _screen.asStateFlow()
 
     private val backStack = mutableListOf<Screen>()
 
     fun navigate(screen: Screen) {
-        backStack.add(_screen.value)
+        val current = _screen.value
+        // Never push Splash onto the back stack
+        if (current !is Screen.Splash) {
+            backStack.add(current)
+        }
         _screen.value = screen
     }
 
     fun navigateBack() {
         if (backStack.isNotEmpty()) {
             _screen.value = backStack.removeLast()
         }
+        // If stack is empty we're at Home — caller handles app exit
     }
 
-    fun canNavigateBack(): Boolean {
-        return backStack.isNotEmpty()
-    }
+    fun canNavigateBack(): Boolean = backStack.isNotEmpty()
+
+    // Home is the root — back from Home should exit the app
+    fun isAtRoot(): Boolean = _screen.value is Screen.Home && backStack.isEmpty()
 
     // ── Theme ─────────────────────────────────────────────────────────────────
 
@@ -104,20 +114,9 @@ class AppStateViewModel : ViewModel() {
     private val _skipMemoryInfo = MutableStateFlow(false)
     val skipMemoryInfo: StateFlow<Boolean> = _skipMemoryInfo.asStateFlow()
 
-    fun setSkipMapInfo(v: Boolean) {
-        _skipMapInfo.value = v
-        prefs.edit { putBoolean("skip_mapInfo", v) }
-    }
-
-    fun setSkipOceanInfo(v: Boolean) {
-        _skipOceanInfo.value = v
-        prefs.edit { putBoolean("skip_oceanInfo", v) }
-    }
-
-    fun setSkipMemoryInfo(v: Boolean) {
-        _skipMemoryInfo.value = v
-        prefs.edit { putBoolean("skip_memoryInfo", v) }
-    }
+    fun setSkipMapInfo(v: Boolean)    { _skipMapInfo.value = v;    prefs.edit { putBoolean("skip_mapInfo", v) } }
+    fun setSkipOceanInfo(v: Boolean)  { _skipOceanInfo.value = v;  prefs.edit { putBoolean("skip_oceanInfo", v) } }
+    fun setSkipMemoryInfo(v: Boolean) { _skipMemoryInfo.value = v; prefs.edit { putBoolean("skip_memoryInfo", v) } }
 
     fun resetPreferences() {
         setSkipMapInfo(false); setSkipOceanInfo(false); setSkipMemoryInfo(false)
@@ -128,4 +127,4 @@ class AppStateViewModel : ViewModel() {
         resetPreferences()
         setTheme(AppTheme.MINT)
     }
-}
+}

app/src/main/java/com/greengo/app/ui/ContentView.kt

@@ -1,5 +1,6 @@
 package com.greengo.app.ui
 
+import androidx.activity.compose.BackHandler
 import androidx.compose.animation.AnimatedContent
 import androidx.compose.animation.ExperimentalAnimationApi
 import androidx.compose.animation.core.tween
@@ -30,17 +31,19 @@ import com.greengo.app.ui.screens.TriviaScoreScreen
 import com.greengo.app.ui.screens.TriviaScreen
 import com.greengo.app.ui.screens.WildRecallScreen
 
-// ─────────────────────────────────────────────────────────────────────────────
-// MARK: - ContentView
-// Root composable: reads screen from ViewModel, renders matching screen.
-// AnimatedContent provides the .easeInOut(duration: 0.22) crossfade equivalent.
-// ─────────────────────────────────────────────────────────────────────────────
-
 @OptIn(ExperimentalAnimationApi::class)
 @Composable
 fun ContentView(vm: AppStateViewModel) {
     val screen by vm.screen.collectAsState()
 
+    // Global back handler:
+    // - On Splash: do nothing (can't go back, splash is one-way)
+    // - On Home with empty stack: do nothing (let Android handle — exits app)
+    // - Everywhere else: pop the back stack
+    BackHandler(enabled = screen !is Screen.Splash && !vm.isAtRoot()) {
+        vm.navigateBack()
+    }
+
     AnimatedContent(
         targetState = screen,
         transitionSpec = {