fix(messaging): Revert "feat(messaging): use FlutterEngineGroup to improve performance of background handlers"

This reverts commit 2e9deac.

Author: Lyokone

packages/firebase_messaging/firebase_messaging/android/src/main/java/io/flutter/plugins/firebase/messaging/FlutterFirebaseMessagingBackgroundExecutor.java

@@ -14,7 +14,7 @@
 import androidx.annotation.NonNull;
 import com.google.firebase.messaging.RemoteMessage;
 import io.flutter.embedding.engine.FlutterEngine;
-import io.flutter.embedding.engine.FlutterEngineGroup;
+import io.flutter.embedding.engine.FlutterShellArgs;
 import io.flutter.embedding.engine.dart.DartExecutor;
 import io.flutter.embedding.engine.dart.DartExecutor.DartCallback;
 import io.flutter.embedding.engine.loader.FlutterLoader;
@@ -24,6 +24,7 @@
 import io.flutter.plugin.common.MethodChannel.MethodCallHandler;
 import io.flutter.plugin.common.MethodChannel.Result;
 import io.flutter.view.FlutterCallbackInformation;
+import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.concurrent.CountDownLatch;
@@ -114,7 +115,7 @@ public void startBackgroundIsolate() {
     if (isNotRunning()) {
       long callbackHandle = getPluginCallbackHandle();
       if (callbackHandle != 0) {
-        startBackgroundIsolate(callbackHandle);
+        startBackgroundIsolate(callbackHandle, null);
       }
     }
   }
@@ -137,7 +138,7 @@ public void startBackgroundIsolate() {
    *       handle does not resolve to a Dart callback then this method does nothing.
    * </ul>
    */
-  public void startBackgroundIsolate(long callbackHandle) {
+  public void startBackgroundIsolate(long callbackHandle, FlutterShellArgs shellArgs) {
     if (backgroundFlutterEngine != null) {
       Log.e(TAG, "Background isolate already started.");
       return;
@@ -156,10 +157,19 @@ public void startBackgroundIsolate(long callbackHandle) {
                 String appBundlePath = loader.findAppBundlePath();
                 AssetManager assets = ContextHolder.getApplicationContext().getAssets();
                 if (isNotRunning()) {
-                  Log.i(TAG, "Creating background FlutterEngine instance.");
-                  backgroundFlutterEngine =
-                      new FlutterEngineGroup(ContextHolder.getApplicationContext())
-                          .createAndRunDefaultEngine(ContextHolder.getApplicationContext());
+                  if (shellArgs != null) {
+                    Log.i(
+                        TAG,
+                        "Creating background FlutterEngine instance, with args: "
+                            + Arrays.toString(shellArgs.toArray()));
+                    backgroundFlutterEngine =
+                        new FlutterEngine(
+                            ContextHolder.getApplicationContext(), shellArgs.toArray());
+                  } else {
+                    Log.i(TAG, "Creating background FlutterEngine instance.");
+                    backgroundFlutterEngine =
+                        new FlutterEngine(ContextHolder.getApplicationContext());
+                  }
                   // We need to create an instance of `FlutterEngine` before looking up the
                   // callback. If we don't, the callback cache won't be initialized and the
                   // lookup will fail.

packages/firebase_messaging/firebase_messaging/android/src/main/java/io/flutter/plugins/firebase/messaging/FlutterFirebaseMessagingBackgroundService.java

@@ -10,6 +10,7 @@
 import android.util.Log;
 import androidx.annotation.NonNull;
 import com.google.firebase.messaging.RemoteMessage;
+import io.flutter.embedding.engine.FlutterShellArgs;
 import java.util.Collections;
 import java.util.LinkedList;
 import java.util.List;
@@ -51,13 +52,13 @@ public static void enqueueMessageProcessing(Context context, Intent messageInten
    * </ul>
    */
   @SuppressWarnings("JavadocReference")
-  public static void startBackgroundIsolate(long callbackHandle) {
+  public static void startBackgroundIsolate(long callbackHandle, FlutterShellArgs shellArgs) {
     if (flutterBackgroundExecutor != null) {
       Log.w(TAG, "Attempted to start a duplicate background isolate. Returning...");
       return;
     }
     flutterBackgroundExecutor = new FlutterFirebaseMessagingBackgroundExecutor();
-    flutterBackgroundExecutor.startBackgroundIsolate(callbackHandle);
+    flutterBackgroundExecutor.startBackgroundIsolate(callbackHandle, shellArgs);
   }
 
   /**

packages/firebase_messaging/firebase_messaging/android/src/main/java/io/flutter/plugins/firebase/messaging/FlutterFirebaseMessagingPlugin.java

@@ -25,6 +25,7 @@
 import com.google.firebase.FirebaseApp;
 import com.google.firebase.messaging.FirebaseMessaging;
 import com.google.firebase.messaging.RemoteMessage;
+import io.flutter.embedding.engine.FlutterShellArgs;
 import io.flutter.embedding.engine.plugins.FlutterPlugin;
 import io.flutter.embedding.engine.plugins.activity.ActivityAware;
 import io.flutter.embedding.engine.plugins.activity.ActivityPluginBinding;
@@ -429,9 +430,19 @@ public void onMethodCall(final MethodCall call, @NonNull final Result result) {
           userCallbackHandle = Long.valueOf((Integer) arg2);
         }
 
+        FlutterShellArgs shellArgs = null;
+        if (mainActivity != null) {
+          // Supports both Flutter Activity types:
+          //    io.flutter.embedding.android.FlutterFragmentActivity
+          //    io.flutter.embedding.android.FlutterActivity
+          // We could use `getFlutterShellArgs()` but this is only available on `FlutterActivity`.
+          shellArgs = FlutterShellArgs.fromIntent(mainActivity.getIntent());
+        }
+
         FlutterFirebaseMessagingBackgroundService.setCallbackDispatcher(pluginCallbackHandle);
         FlutterFirebaseMessagingBackgroundService.setUserCallbackHandle(userCallbackHandle);
-        FlutterFirebaseMessagingBackgroundService.startBackgroundIsolate(pluginCallbackHandle);
+        FlutterFirebaseMessagingBackgroundService.startBackgroundIsolate(
+            pluginCallbackHandle, shellArgs);
         methodCallTask = Tasks.forResult(null);
         break;
       case "Messaging#getInitialMessage":