Android: close screens left open when the app is reopened from the launcher

android/app/src/main/kotlin/wtf/openstrap/openstrap_edge/MainActivity.kt

@@ -4,6 +4,8 @@ import android.content.Context
 import android.content.Intent
 import android.os.Bundle
 import io.flutter.embedding.android.FlutterFragmentActivity
+import io.flutter.embedding.engine.FlutterEngineCache
+import io.flutter.plugin.common.MethodChannel
 
 /**
  * Attaches to the single long-lived engine owned by [EdgeApplication] (created lazily
@@ -27,19 +29,39 @@ class MainActivity : FlutterFragmentActivity() {
     companion object {
         @Volatile
         var activityAttached: Boolean = false
+
+        /** Dart side: lib/platform/activity_relaunch.dart. */
+        private const val ACTIVITY_CHANNEL = "openstrap/activity"
     }
 
     override fun getCachedEngineId(): String = EdgeApplication.ENGINE_ID
     override fun shouldDestroyEngineWithHost(): Boolean = false
 
     override fun onCreate(savedInstanceState: Bundle?) {
+        // Read BEFORE ensureEngine: true means this Activity attaches to a Dart side
+        // that outlived the previous one, screens and all (see the class doc).
+        val engineOutlivedActivity =
+            FlutterEngineCache.getInstance().get(EdgeApplication.ENGINE_ID) != null
         // The shared engine is created lazily now (EdgeApplication.ensureEngine).
         // getCachedEngineId() is consulted during super.onCreate, so the cache
         // entry must exist before it runs.
-        EdgeApplication.ensureEngine(applicationContext)
+        val engine = EdgeApplication.ensureEngine(applicationContext)
         activityAttached = true
         clearPendingHeadlessBoot()
         super.onCreate(savedInstanceState)
+        // Opened again from the launcher after the app was closed: the retained engine
+        // still has whatever screen was on top (issue #650), where iOS — whose process
+        // ends — would start fresh on the saved tab. Ask Dart to close those screens.
+        // Not on a restore (savedInstanceState: Android recreated us and expects the
+        // screen back), and not for notification/widget taps, whose own action routes
+        // them. Rotation and dark mode never get here (configChanges in the manifest).
+        if (engineOutlivedActivity && savedInstanceState == null &&
+            intent?.action == Intent.ACTION_MAIN &&
+            intent?.hasCategory(Intent.CATEGORY_LAUNCHER) == true
+        ) {
+            MethodChannel(engine.dartExecutor.binaryMessenger, ACTIVITY_CHANNEL)
+                .invokeMethod("relaunched", null)
+        }
         CompanionBridge.currentActivity = this
         // Re-arm CDM device-presence observation for an already-associated band
         // (idempotent; no-op below API 31 or when nothing is associated).

lib/app.dart

@@ -10,6 +10,7 @@ import 'data/db.dart';
 import 'l10n/app_localizations.dart';
 import 'notify/notification_service.dart';
 import 'notify/tap_router.dart';
+import 'platform/activity_relaunch.dart';
 import 'state/app_state.dart';
 import 'state/clock_format.dart';
 import 'state/locale_controller.dart';
@@ -539,6 +540,9 @@ class _ShellState extends State<_Shell> {
     _selection = ValueNotifier(_domain);
     _app!.navRequest.addListener(_consumeSoon);
     _app!.screenRequest.addListener(_consumeSoon);
+    // Android relaunch from the launcher: close screens left open on the
+    // engine that outlived the closed Activity (#650).
+    ActivityRelaunch.listen(_relaunchNavigator);
     // Cold launch from a tapped notification: the route may already be set
     // before this shell mounted (so the listener never fired). Consume it once
     // attached.
@@ -551,6 +555,9 @@ class _ShellState extends State<_Shell> {
     });
   }
 
+  NavigatorState? _relaunchNavigator() =>
+      mounted ? Navigator.of(context) : null;
+
   bool _pending = false;
 
   /// Both requests come from ONE tap and are written one after the other, so
@@ -604,6 +611,7 @@ class _ShellState extends State<_Shell> {
   void dispose() {
     _app?.navRequest.removeListener(_consumeSoon);
     _app?.screenRequest.removeListener(_consumeSoon);
+    ActivityRelaunch.stop(_relaunchNavigator);
     _selection.dispose();
     super.dispose();
   }

lib/platform/activity_relaunch.dart

@@ -0,0 +1,37 @@
+import 'package:flutter/services.dart';
+import 'package:flutter/widgets.dart';
+
+/// Android: the launcher opened the app again after it was closed (issue #650).
+///
+/// The Activity goes away when the app is swiped from recents, but the Flutter
+/// engine is kept alive for background Bluetooth, so the Navigator still holds
+/// whatever screen was on top: reopening landed back inside Settings. On iOS the
+/// process ends and a relaunch starts on the saved tab with nothing above it.
+/// `MainActivity.onCreate` sends `relaunched` only for that case, and this
+/// closes the pushed screens to match. The tab itself is left alone: it is
+/// restored on purpose (`restoredShellTab`).
+class ActivityRelaunch {
+  static const channel = MethodChannel('openstrap/activity');
+
+  static NavigatorState? Function()? _navigator;
+
+  /// Handle `relaunched` while [navigator] can answer; it returns null once its
+  /// owner is gone. Pass the same function to [stop] when the owner is disposed.
+  static void listen(NavigatorState? Function() navigator) {
+    _navigator = navigator;
+    channel.setMethodCallHandler((call) async {
+      if (call.method != 'relaunched') return;
+      _navigator?.call()?.popUntil((route) => route.isFirst);
+    });
+  }
+
+  /// Stops listening, unless a newer owner has called [listen] since: a
+  /// replaced owner's dispose runs after its successor's initState.
+  static void stop(NavigatorState? Function() navigator) {
+    // `!=`, not `identical`: two tear-offs of one instance's method are equal
+    // but not guaranteed identical.
+    if (_navigator != navigator) return;
+    _navigator = null;
+    channel.setMethodCallHandler(null);
+  }
+}

test/activity_relaunch_test.dart

@@ -0,0 +1,86 @@
+// #650: on Android the Flutter engine outlives the Activity, so a screen left
+// open (Settings, a detail page) was still on top when the app was opened
+// again from the launcher. `MainActivity` sends `relaunched` on
+// `openstrap/activity` for exactly that case; the Dart side closes the pushed
+// screens and leaves the tab underneath alone, as an iOS cold start would.
+
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:openstrap_edge/platform/activity_relaunch.dart';
+
+void main() {
+  final navKey = GlobalKey<NavigatorState>();
+  NavigatorState? nav() => navKey.currentState;
+
+  Future<void> fromNative(WidgetTester tester, String method) async {
+    await tester.binding.defaultBinaryMessenger.handlePlatformMessage(
+      ActivityRelaunch.channel.name,
+      const StandardMethodCodec().encodeMethodCall(MethodCall(method)),
+      (_) {},
+    );
+    await tester.pumpAndSettle();
+  }
+
+  Future<void> openTwoScreens(WidgetTester tester) async {
+    await tester.pumpWidget(MaterialApp(
+      navigatorKey: navKey,
+      home: const Text('tab'),
+    ));
+    for (final name in ['settings', 'detail']) {
+      navKey.currentState!
+          .push(MaterialPageRoute<void>(builder: (_) => Text(name)));
+      await tester.pumpAndSettle();
+    }
+    expect(find.text('detail'), findsOneWidget);
+  }
+
+  tearDown(() => ActivityRelaunch.stop(nav));
+
+  testWidgets('relaunched closes every pushed screen, back to the tab',
+      (tester) async {
+    await openTwoScreens(tester);
+    ActivityRelaunch.listen(nav);
+
+    await fromNative(tester, 'relaunched');
+
+    expect(find.text('tab'), findsOneWidget);
+    expect(find.text('settings'), findsNothing);
+    expect(find.text('detail'), findsNothing);
+  });
+
+  testWidgets('any other call leaves the screens alone', (tester) async {
+    await openTwoScreens(tester);
+    ActivityRelaunch.listen(nav);
+
+    await fromNative(tester, 'something_else');
+
+    expect(find.text('detail'), findsOneWidget);
+  });
+
+  testWidgets('a disposed owner (null navigator) is a no-op, not a crash',
+      (tester) async {
+    await openTwoScreens(tester);
+    NavigatorState? gone() => null;
+    ActivityRelaunch.listen(gone);
+
+    await fromNative(tester, 'relaunched');
+
+    expect(find.text('detail'), findsOneWidget);
+    ActivityRelaunch.stop(gone);
+  });
+
+  testWidgets("a replaced owner's stop does not silence its successor",
+      (tester) async {
+    await openTwoScreens(tester);
+    NavigatorState? old() => null;
+    ActivityRelaunch.listen(old);
+    ActivityRelaunch.listen(nav); // successor's initState
+    ActivityRelaunch.stop(old); // predecessor's later dispose
+
+    await fromNative(tester, 'relaunched');
+
+    expect(find.text('tab'), findsOneWidget);
+  });
+}