Fix/communication between app and overlay

README.md

@@ -109,14 +109,25 @@ void overlayMain() {
  /// closes overlay if open
  await FlutterOverlayWindow.closeOverlay();
 
- /// broadcast data to and from overlay app
+ /// Broadcast data to and from overlay app.
+ /// This method may return `false` when invoked from the overlay while the application is closed.
+ /// Returns `true` if the data was sent successfully, otherwise `false`.
  await FlutterOverlayWindow.shareData("Hello from the other side");
 
  /// streams message shared between overlay and main app
   FlutterOverlayWindow.overlayListener.listen((event) {
       log("Current Event: $event");
     });
 
+ /// Overlay status stream.
+ /// Emit `true` when overlay is showing, and `false` when overlay is closed.
+ /// Emit value only once for every state change.
+ /// Doesn't emit a change when the overlay is already showing and [showOverlay] is called,
+ /// as in this case the overlay will almost immediately reopen.
+  FlutterOverlayWindow.overlayStatusListener.listen((event) {
+      print("Overlay status: $event");
+    });
+
  /// use [OverlayFlag.focusPointer] when you want to use fields that show keyboards
  await FlutterOverlayWindow.showOverlay(flag: OverlayFlag.focusPointer);
 

android/src/main/java/flutter/overlay/window/flutter_overlay_window/CachedMessageChannels.java

@@ -0,0 +1,11 @@
+package flutter.overlay.window.flutter_overlay_window;
+
+import androidx.annotation.Nullable;
+import io.flutter.plugin.common.MethodChannel;
+
+public abstract class CachedMessageChannels {
+    @Nullable
+    public static MethodChannel mainAppMessageChannel;
+    @Nullable
+    public static MethodChannel overlayMessageChannel;
+}

android/src/main/java/flutter/overlay/window/flutter_overlay_window/FlutterOverlayWindowPlugin.java

@@ -1,12 +1,12 @@
 package flutter.overlay.window.flutter_overlay_window;
 
 import android.app.Activity;
-import android.app.NotificationManager;
 import android.content.Context;
 import android.content.Intent;
 import android.net.Uri;
 import android.os.Build;
 import android.provider.Settings;
+
 import android.service.notification.StatusBarNotification;
 import android.util.Log;
 import android.view.WindowManager;
@@ -16,47 +16,50 @@
 import androidx.annotation.RequiresApi;
 import androidx.core.app.NotificationManagerCompat;
 
+import java.util.Objects;
 import java.util.Map;
 
 import io.flutter.FlutterInjector;
 import io.flutter.embedding.engine.FlutterEngine;
 import io.flutter.embedding.engine.FlutterEngineCache;
 import io.flutter.embedding.engine.FlutterEngineGroup;
+import io.flutter.embedding.engine.FlutterEngineGroupCache;
 import io.flutter.embedding.engine.dart.DartExecutor;
 import io.flutter.embedding.engine.plugins.FlutterPlugin;
 import io.flutter.embedding.engine.plugins.activity.ActivityAware;
 import io.flutter.embedding.engine.plugins.activity.ActivityPluginBinding;
-import io.flutter.plugin.common.BasicMessageChannel;
-import io.flutter.plugin.common.JSONMessageCodec;
+import io.flutter.plugin.common.JSONMethodCodec;
 import io.flutter.plugin.common.MethodCall;
 import io.flutter.plugin.common.MethodChannel;
 import io.flutter.plugin.common.MethodChannel.MethodCallHandler;
 import io.flutter.plugin.common.MethodChannel.Result;
 import io.flutter.plugin.common.PluginRegistry;
 
 public class FlutterOverlayWindowPlugin implements
-        FlutterPlugin, ActivityAware, BasicMessageChannel.MessageHandler, MethodCallHandler,
+        FlutterPlugin, ActivityAware, MethodCallHandler,
         PluginRegistry.ActivityResultListener {
 
     private MethodChannel channel;
     private Context context;
     private Activity mActivity;
-    private BasicMessageChannel<Object> messenger;
     private Result pendingResult;
     final int REQUEST_CODE_FOR_OVERLAY_PERMISSION = 1248;
+    @Nullable
+    FlutterPluginBinding flutterBinding;
+    @Nullable
+    ActivityPluginBinding activityPluginBinding;
+    boolean isMainAppEngine;
 
     @Override
     public void onAttachedToEngine(@NonNull FlutterPluginBinding flutterPluginBinding) {
+        flutterBinding = flutterPluginBinding;
         this.context = flutterPluginBinding.getApplicationContext();
         channel = new MethodChannel(flutterPluginBinding.getBinaryMessenger(), OverlayConstants.CHANNEL_TAG);
         channel.setMethodCallHandler(this);
 
-        messenger = new BasicMessageChannel(flutterPluginBinding.getBinaryMessenger(), OverlayConstants.MESSENGER_TAG,
-                JSONMessageCodec.INSTANCE);
-        messenger.setMessageHandler(this);
-
-        WindowSetup.messenger = messenger;
-        WindowSetup.messenger.setMessageHandler(this);
+        FlutterEngineGroup overlayEngineGroup = ensureEngineGroupCreated(context);
+        isMainAppEngine = flutterBinding.getEngineGroup() != overlayEngineGroup;
+        registerMessageChannel(isMainAppEngine);
     }
 
     @RequiresApi(api = Build.VERSION_CODES.N)
@@ -78,6 +81,9 @@ public void onMethodCall(@NonNull MethodCall call, @NonNull Result result) {
                 result.error("PERMISSION", "overlay permission is not enabled", null);
                 return;
             }
+
+            ensureEngineCreated(context);
+
             Integer height = call.argument("height");
             Integer width = call.argument("width");
             String alignment = call.argument("alignment");
@@ -131,50 +137,121 @@ public void onMethodCall(@NonNull MethodCall call, @NonNull Result result) {
         } else {
             result.notImplemented();
         }
-
     }
 
     @Override
     public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {
         channel.setMethodCallHandler(null);
-        WindowSetup.messenger.setMessageHandler(null);
+        flutterBinding = null;
+        unregisterMessageChannel(isMainAppEngine);
+        FlutterEngineGroupCache.getInstance().remove(OverlayConstants.CACHED_TAG);
     }
 
     @Override
     public void onAttachedToActivity(@NonNull ActivityPluginBinding binding) {
+        activityPluginBinding = binding;
         mActivity = binding.getActivity();
-        if (FlutterEngineCache.getInstance().get(OverlayConstants.CACHED_TAG) == null) {
-            FlutterEngineGroup enn = new FlutterEngineGroup(context);
-            DartExecutor.DartEntrypoint dEntry = new DartExecutor.DartEntrypoint(
-                    FlutterInjector.instance().flutterLoader().findAppBundlePath(),
-                    "overlayMain");
-            FlutterEngine engine = enn.createAndRunEngine(context, dEntry);
-            FlutterEngineCache.getInstance().put(OverlayConstants.CACHED_TAG, engine);
-        }
+
+        ensureEngineCreated(context);
+
+        binding.addActivityResultListener(this);
     }
 
     @Override
     public void onDetachedFromActivityForConfigChanges() {
+        onDetachedFromActivity();
     }
 
     @Override
     public void onReattachedToActivityForConfigChanges(@NonNull ActivityPluginBinding binding) {
-        this.mActivity = binding.getActivity();
+        onAttachedToActivity(binding);
     }
 
     @Override
     public void onDetachedFromActivity() {
+        Objects.requireNonNull(activityPluginBinding).removeActivityResultListener(this);
+        activityPluginBinding = null;
+        mActivity = null;
     }
 
-    @Override
-    public void onMessage(@Nullable Object message, @NonNull BasicMessageChannel.Reply reply) {
-        BasicMessageChannel overlayMessageChannel = new BasicMessageChannel(
-                FlutterEngineCache.getInstance().get(OverlayConstants.CACHED_TAG)
-                        .getDartExecutor(),
-                OverlayConstants.MESSENGER_TAG, JSONMessageCodec.INSTANCE);
-        overlayMessageChannel.send(message, reply);
+    private void registerMessageChannel(boolean isMainAppEngine) {
+        io.flutter.plugin.common.BinaryMessenger binaryMessenger = Objects.requireNonNull(flutterBinding).getBinaryMessenger();
+        if(isMainAppEngine) {
+            registerMainAppMessageChannel(binaryMessenger);
+        } else {
+            registerOverlayMessageChannel(binaryMessenger);
+        }
+    }
+
+    private void unregisterMessageChannel(boolean isMainAppEngine) {
+        if(isMainAppEngine) {
+            if (CachedMessageChannels.mainAppMessageChannel == null) return;
+            CachedMessageChannels.mainAppMessageChannel.setMethodCallHandler(null);
+            CachedMessageChannels.mainAppMessageChannel = null;
+        } else {
+            if(CachedMessageChannels.overlayMessageChannel == null) return;
+            CachedMessageChannels.overlayMessageChannel.setMethodCallHandler(null);
+            CachedMessageChannels.overlayMessageChannel = null;
+        }
     }
 
+    private void registerOverlayMessageChannel(io.flutter.plugin.common.BinaryMessenger overlyEngineBinaryMessenger) {
+        MethodChannel overlayMessageChannel = new MethodChannel(overlyEngineBinaryMessenger, OverlayConstants.MESSENGER_TAG, JSONMethodCodec.INSTANCE);
+        overlayMessageChannel.setMethodCallHandler((call, result) -> {
+            if (CachedMessageChannels.mainAppMessageChannel == null) {
+                result.success(false);
+                return;
+            }
+            CachedMessageChannels.mainAppMessageChannel.invokeMethod("message", call.arguments);
+            result.success(true);
+        });
+        CachedMessageChannels.overlayMessageChannel = overlayMessageChannel;
+    }
+
+    private void registerMainAppMessageChannel(io.flutter.plugin.common.BinaryMessenger mainAppEngineBinaryMessenger) {
+        MethodChannel mainAppMessageChannel = new MethodChannel(mainAppEngineBinaryMessenger, OverlayConstants.MESSENGER_TAG, JSONMethodCodec.INSTANCE);
+        mainAppMessageChannel.setMethodCallHandler((call, result) -> {
+            if (CachedMessageChannels.overlayMessageChannel == null) {
+                result.success(false);
+                return;
+            }
+            CachedMessageChannels.overlayMessageChannel.invokeMethod("message", call.arguments);
+            result.success(true);
+        });
+        CachedMessageChannels.mainAppMessageChannel = mainAppMessageChannel;
+    }
+
+    private FlutterEngineGroup ensureEngineGroupCreated(android.content.Context context) {
+        FlutterEngineGroup enn = FlutterEngineGroupCache.getInstance().get(OverlayConstants.CACHED_TAG);
+
+        if(enn == null) {
+            enn = new FlutterEngineGroup(context);
+            FlutterEngineGroupCache.getInstance().put(OverlayConstants.CACHED_TAG, enn);
+        }
+
+        return enn;
+    }
+    private void ensureEngineCreated(android.content.Context context) {
+        FlutterEngine engine = FlutterEngineCache.getInstance().get(OverlayConstants.CACHED_TAG);
+        if(engine == null) {
+            FlutterEngineGroup enn = ensureEngineGroupCreated(context);
+            DartExecutor.DartEntrypoint dEntry = new DartExecutor.DartEntrypoint(
+                    FlutterInjector.instance().flutterLoader().findAppBundlePath(),
+                    "overlayMain");
+            engine = Objects.requireNonNull(enn).createAndRunEngine(context, dEntry);
+            FlutterEngineCache.getInstance().put(OverlayConstants.CACHED_TAG, engine);
+            engine.addEngineLifecycleListener(new  FlutterEngine.EngineLifecycleListener() {
+                @Override
+                public void onPreEngineRestart() {
+
+                }
+                @Override
+                public void onEngineWillDestroy() {
+                    FlutterEngineCache.getInstance().remove(OverlayConstants.CACHED_TAG);
+                }
+            });
+        }
+    }
     private boolean checkOverlayPermission() {
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
             return Settings.canDrawOverlays(context);

android/src/main/java/flutter/overlay/window/flutter_overlay_window/OverlayService.java

@@ -37,8 +37,6 @@
 import io.flutter.embedding.android.FlutterView;
 import io.flutter.embedding.engine.FlutterEngine;
 import io.flutter.embedding.engine.FlutterEngineCache;
-import io.flutter.plugin.common.BasicMessageChannel;
-import io.flutter.plugin.common.JSONMessageCodec;
 import io.flutter.plugin.common.MethodChannel;
 
 public class OverlayService extends Service implements View.OnTouchListener {
@@ -56,7 +54,6 @@ public class OverlayService extends Service implements View.OnTouchListener {
     private WindowManager windowManager = null;
     private FlutterView flutterView;
     private MethodChannel flutterChannel = new MethodChannel(FlutterEngineCache.getInstance().get(OverlayConstants.CACHED_TAG).getDartExecutor(), OverlayConstants.OVERLAY_TAG);
-    private BasicMessageChannel<Object> overlayMessageChannel = new BasicMessageChannel(FlutterEngineCache.getInstance().get(OverlayConstants.CACHED_TAG).getDartExecutor(), OverlayConstants.MESSENGER_TAG, JSONMessageCodec.INSTANCE);
     private int clickableFlag = WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE |
             WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS | WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN;
 
@@ -79,15 +76,19 @@ public IBinder onBind(Intent intent) {
     @Override
     public void onDestroy() {
         Log.d("OverLay", "Destroying the overlay window service");
-        if (windowManager != null) {
+        isRunning = false;
+        if(windowManager != null && flutterView != null) {
             windowManager.removeView(flutterView);
             windowManager = null;
+        }
+        if(flutterView != null) {
             flutterView.detachFromFlutterEngine();
             flutterView = null;
         }
-        isRunning = false;
+        OverlayStatusEmitter.emitIsShowing(false);
         NotificationManager notificationManager = (NotificationManager) getApplicationContext().getSystemService(Context.NOTIFICATION_SERVICE);
         notificationManager.cancel(OverlayConstants.NOTIFICATION_ID);
+
         instance = null;
     }
 
@@ -99,20 +100,16 @@ public int onStartCommand(Intent intent, int flags, int startId) {
         int startY = intent.getIntExtra("startY", OverlayConstants.DEFAULT_XY);
         boolean isCloseWindow = intent.getBooleanExtra(INTENT_EXTRA_IS_CLOSE_WINDOW, false);
         if (isCloseWindow) {
-            if (windowManager != null) {
-                windowManager.removeView(flutterView);
-                windowManager = null;
-                flutterView.detachFromFlutterEngine();
-                stopSelf();
-            }
-            isRunning = false;
+            stopSelf();
             return START_STICKY;
         }
-        if (windowManager != null) {
+        if(windowManager != null && flutterView != null) {
             windowManager.removeView(flutterView);
             windowManager = null;
+        }
+        if(flutterView != null) {
             flutterView.detachFromFlutterEngine();
-            stopSelf();
+            flutterView = null;
         }
         isRunning = true;
         Log.d("onStartCommand", "Service started");
@@ -139,9 +136,7 @@ public int onStartCommand(Intent intent, int flags, int startId) {
                 resizeOverlay(width, height, enableDrag, result);
             }
         });
-        overlayMessageChannel.setMessageHandler((message, reply) -> {
-            WindowSetup.messenger.send(message);
-        });
+
         windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
 
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
@@ -174,6 +169,7 @@ public int onStartCommand(Intent intent, int flags, int startId) {
         flutterView.setOnTouchListener(this);
         windowManager.addView(flutterView, params);
         moveOverlay(dx, dy, null);
+        OverlayStatusEmitter.emitIsShowing(true);
         return START_STICKY;
     }
 

android/src/main/java/flutter/overlay/window/flutter_overlay_window/OverlayStatusEmitter.java

@@ -0,0 +1,17 @@
+package flutter.overlay.window.flutter_overlay_window;
+
+public abstract class OverlayStatusEmitter {
+    static private final String methodName = "isShowingOverlay";
+    static private boolean lastEmittedStatus;
+
+    static void emitIsShowing(boolean isShowing) {
+        if(isShowing == lastEmittedStatus) return;
+        lastEmittedStatus = isShowing;
+        if(CachedMessageChannels.mainAppMessageChannel != null) {
+            CachedMessageChannels.mainAppMessageChannel.invokeMethod(methodName, isShowing);
+        }
+        if(CachedMessageChannels.overlayMessageChannel != null) {
+            CachedMessageChannels.overlayMessageChannel.invokeMethod(methodName, isShowing);
+        }
+    }
+}

android/src/main/java/flutter/overlay/window/flutter_overlay_window/WindowSetup.java

@@ -3,18 +3,14 @@
 
 import android.view.Gravity;
 import android.view.WindowManager;
-
 import androidx.core.app.NotificationCompat;
 
-import io.flutter.plugin.common.BasicMessageChannel;
-
 public abstract class WindowSetup {
 
     static int height = WindowManager.LayoutParams.MATCH_PARENT;
     static int width = WindowManager.LayoutParams.MATCH_PARENT;
     static int flag = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;
     static int gravity = Gravity.CENTER;
-    static BasicMessageChannel<Object> messenger = null;
     static String overlayTitle = "Overlay is activated";
     static String overlayContent = "Tap to edit settings or disable";
     static String positionGravity = "none";