fix(messaging,android): fix an issue that could cause duplicate call stack

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

@@ -9,7 +9,6 @@
 import android.os.Handler;
 import android.util.Log;
 import androidx.annotation.NonNull;
-import io.flutter.embedding.engine.FlutterShellArgs;
 import java.util.Collections;
 import java.util.LinkedList;
 import java.util.List;
@@ -37,28 +36,6 @@ public static void enqueueMessageProcessing(
         isHighPriority);
   }
 
-  /**
-   * Starts the background isolate for the {@link FlutterFirebaseMessagingBackgroundService}.
-   *
-   * <p>Preconditions:
-   *
-   * <ul>
-   *   <li>The given {@code callbackHandle} must correspond to a registered Dart callback. If the
-   *       handle does not resolve to a Dart callback then this method does nothing.
-   *   <li>A static {@link #pluginRegistrantCallback} must exist, otherwise a {@link
-   *       PluginRegistrantException} will be thrown.
-   * </ul>
-   */
-  @SuppressWarnings("JavadocReference")
-  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, shellArgs);
-  }
-
   /**
    * Called once the Dart isolate ({@code flutterBackgroundExecutor}) has finished initializing.
    *

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

@@ -23,7 +23,6 @@
 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;
@@ -421,12 +420,9 @@ public void onMethodCall(final MethodCall call, @NonNull final Result result) {
     Task<?> methodCallTask;
 
     switch (call.method) {
-        // This message is sent when the Dart side of this plugin is told to initialize.
-        // In response, this (native) side of the plugin needs to spin up a background
-        // Dart isolate by using the given pluginCallbackHandle, and then setup a background
-        // method channel to communicate with the new background isolate. Once completed,
-        // this onMethodCall() method will receive messages from both the primary and background
-        // method channels.
+        // This message is sent when the Dart side of this plugin registers a background
+        // message handler. We persist the callback handles to SharedPreferences so
+        // the background service can start the isolate later when a message arrives.
       case "Messaging#startBackgroundIsolate":
         @SuppressWarnings("unchecked")
         Map<String, Object> arguments = ((Map<String, Object>) call.arguments);
@@ -455,19 +451,13 @@ public void onMethodCall(final MethodCall call, @NonNull final Result result) {
               "Expected 'Long' or 'Integer' type for 'userCallbackHandle'.");
         }
 
-        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());
-        }
-
+        // Only save the callback handles to SharedPreferences. Don't start the
+        // background isolate here — it will be started lazily in
+        // FlutterFirebaseMessagingBackgroundService.onCreate() when a background
+        // message actually arrives and the service is started. Starting it eagerly
+        // caused a duplicate Dart main() to appear in the call stack (#17163).
         FlutterFirebaseMessagingBackgroundService.setCallbackDispatcher(pluginCallbackHandle);
         FlutterFirebaseMessagingBackgroundService.setUserCallbackHandle(userCallbackHandle);
-        FlutterFirebaseMessagingBackgroundService.startBackgroundIsolate(
-            pluginCallbackHandle, shellArgs);
         methodCallTask = Tasks.forResult(null);
         break;
       case "Messaging#getInitialMessage":

packages/firebase_messaging/firebase_messaging/example/android/app/build.gradle

@@ -47,7 +47,7 @@ android {
         applicationId = "io.flutter.plugins.firebase.messaging.example"
         // You can update the following values to match your application needs.
         // For more information, see: https://docs.flutter.dev/deployment/android#reviewing-the-gradle-build-configuration.
-        minSdk = 23
+        minSdkVersion = flutter.minSdkVersion
         targetSdk = flutter.targetSdkVersion
         versionCode = flutterVersionCode.toInteger()
         versionName = flutterVersionName