fix(firebase_messaging): Support Android v2 embedding

packages/firebase_messaging/CHANGELOG.md

@@ -1,3 +1,12 @@
+## 8.0.0
+
+* Add support for Android v2 embedding.
+* **Breaking Change** This will cause applications with v2 embedding that declare the background handler and
+  call `FlutterFirebaseMessagingService.setPluginRegistrant` in their `Application.java` `onCreate` method
+  to crash on startup or when receiving background notifications.
+  To have this plugin work with these applications, you can read the updated README or
+  you can delete your `Application.java` and remove the `android:name=".Application"` reference in your manifest.
+
 ## 7.0.2
 
  - **FIX**: remove `platform` package usage (#3729).

packages/firebase_messaging/README.md

@@ -73,42 +73,6 @@ By default background messaging is not enabled. To handle messages in the backgr
 
    Note: you can find out what the latest version of the plugin is [here ("Cloud Messaging")](https://firebase.google.com/support/release-notes/android#latest_sdk_versions).
 
-1. Add an `Application.java` class to your app in the same directory as your `MainActivity.java`. This is typically found in `<app-name>/android/app/src/main/java/<app-organization-path>/`.
-
-   ```java
-   package io.flutter.plugins.firebasemessagingexample;
-
-   import io.flutter.app.FlutterApplication;
-   import io.flutter.plugin.common.PluginRegistry;
-   import io.flutter.plugin.common.PluginRegistry.PluginRegistrantCallback;
-   import io.flutter.plugins.GeneratedPluginRegistrant;
-   import io.flutter.plugins.firebasemessaging.FlutterFirebaseMessagingService;
-
-   public class Application extends FlutterApplication implements PluginRegistrantCallback {
-     @Override
-     public void onCreate() {
-       super.onCreate();
-       FlutterFirebaseMessagingService.setPluginRegistrant(this);
-     }
-
-     @Override
-     public void registerWith(PluginRegistry registry) {
-       GeneratedPluginRegistrant.registerWith(registry);
-     }
-   }
-   ```
-
-1. In `Application.java`, make sure to change `package io.flutter.plugins.firebasemessagingexample;` to your package's identifier. Your package's identifier should be something like `com.domain.myapplication`.
-
-   ```java
-   package com.domain.myapplication;
-   ```
-
-1. Set name property of application in `AndroidManifest.xml`. This is typically found in `<app-name>/android/app/src/main/`.
-
-   ```xml
-   <application android:name=".Application" ...>
-   ```
 
 1. Define a **TOP-LEVEL** or **STATIC** function to handle background messages
 
@@ -155,6 +119,51 @@ By default background messaging is not enabled. To handle messages in the backgr
    so that it can be ready to receive messages as early as possible. See the
    [example app](https://github.com/FirebaseExtended/flutterfire/tree/master/packages/firebase_messaging/example) for a demonstration.
 
+
+>If you are using a Flutter version prior to 1.12 or you are using v1 embedding, you need to complete additional steps.
+For more information about v1/v2 embedding, check [Upgrading pre 1.12 Android](https://github.com/flutter/flutter/wiki/Upgrading-pre-1.12-Android-projects).
+
+Additional steps for v1 embedding:
+
+1. Add an `Application.java` class to your app in the same directory as your `MainActivity.java`. This is typically found in `<app-name>/android/app/src/main/java/<app-organization-path>/`.
+
+   ```java
+   package io.flutter.plugins.firebasemessagingexample;
+
+   import io.flutter.app.FlutterApplication;
+   import io.flutter.plugin.common.PluginRegistry;
+   import io.flutter.plugin.common.PluginRegistry.PluginRegistrantCallback;
+   import io.flutter.plugins.GeneratedPluginRegistrant;
+   import io.flutter.plugins.firebasemessaging.FlutterFirebaseMessagingService;
+
+   public class Application extends FlutterApplication implements PluginRegistrantCallback {
+     @Override
+     public void onCreate() {
+       super.onCreate();
+       FlutterFirebaseMessagingService.setPluginRegistrant(this);
+     }
+
+     @Override
+     public void registerWith(PluginRegistry registry) {
+       GeneratedPluginRegistrant.registerWith(registry);
+     }
+   }
+   ```
+
+   Note: Calls to `FlutterFirebaseMessagingService.setPluginRegistrant` while using v2 embedding will result in a build time error.
+
+1. In `Application.java`, make sure to change `package io.flutter.plugins.firebasemessagingexample;` to your package's identifier. Your package's identifier should be something like `com.domain.myapplication`.
+
+   ```java
+   package com.domain.myapplication;
+   ```
+
+1. Set name property of application in `AndroidManifest.xml`. This is typically found in `<app-name>/android/app/src/main/`.
+
+   ```xml
+   <application android:name=".Application" ...>
+   ```
+
 ### iOS Integration
 
 To integrate your plugin into the iOS part of your app, follow these steps:

packages/firebase_messaging/android/src/main/java/io/flutter/plugins/firebasemessaging/FirebaseMessagingPlugin.java

@@ -54,12 +54,10 @@ public static void registerWith(Registrar registrar) {
   private void onAttachedToEngine(Context context, BinaryMessenger binaryMessenger) {
     this.applicationContext = context;
     channel = new MethodChannel(binaryMessenger, "plugins.flutter.io/firebase_messaging");
-    final MethodChannel backgroundCallbackChannel =
-        new MethodChannel(binaryMessenger, "plugins.flutter.io/firebase_messaging_background");
-
     channel.setMethodCallHandler(this);
-    backgroundCallbackChannel.setMethodCallHandler(this);
-    FlutterFirebaseMessagingService.setBackgroundChannel(backgroundCallbackChannel);
+
+    //Add reference to this class as the MethodCallHandler
+    FlutterFirebaseMessagingService.setFirebaseMessagingPlugin(this);
 
     // Register broadcast receiver
     IntentFilter intentFilter = new IntentFilter();
@@ -69,6 +67,21 @@ private void onAttachedToEngine(Context context, BinaryMessenger binaryMessenger
     manager.registerReceiver(this, intentFilter);
   }
 
+  public void initializeBackgroundMethodChannel(BinaryMessenger binaryMessenger) {
+
+    // backgroundChannel is the channel responsible for receiving the following messages from
+    // the background isolate that was setup by this plugin:
+    // - "FcmDartService#initialized"
+    //
+    // This channel is also responsible for sending requests from Android to Dart to execute Dart
+    // callbacks in the background isolate.
+    final MethodChannel backgroundCallbackChannel =
+        new MethodChannel(binaryMessenger, "plugins.flutter.io/firebase_messaging_background");
+    backgroundCallbackChannel.setMethodCallHandler(this);
+
+    FlutterFirebaseMessagingService.setBackgroundChannel(backgroundCallbackChannel);
+  }
+
   private void setActivity(Activity flutterActivity) {
     this.mainActivity = flutterActivity;
   }

packages/firebase_messaging/android/src/main/java/io/flutter/plugins/firebasemessaging/FlutterFirebaseMessagingService.java

@@ -9,18 +9,21 @@
 import android.content.Context;
 import android.content.Intent;
 import android.content.SharedPreferences;
+import android.content.res.AssetManager;
 import android.os.Handler;
 import android.os.Process;
 import android.util.Log;
 import androidx.localbroadcastmanager.content.LocalBroadcastManager;
 import com.google.firebase.messaging.FirebaseMessagingService;
 import com.google.firebase.messaging.RemoteMessage;
+import io.flutter.embedding.engine.FlutterEngine;
+import io.flutter.embedding.engine.dart.DartExecutor;
+import io.flutter.embedding.engine.dart.DartExecutor.DartCallback;
+import io.flutter.embedding.engine.plugins.shim.ShimPluginRegistry;
 import io.flutter.plugin.common.MethodChannel;
 import io.flutter.plugin.common.PluginRegistry;
 import io.flutter.view.FlutterCallbackInformation;
 import io.flutter.view.FlutterMain;
-import io.flutter.view.FlutterNativeView;
-import io.flutter.view.FlutterRunArguments;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Iterator;
@@ -47,8 +50,7 @@ public class FlutterFirebaseMessagingService extends FirebaseMessagingService {
   // TODO(kroikie): make isIsolateRunning per-instance, not static.
   private static AtomicBoolean isIsolateRunning = new AtomicBoolean(false);
 
-  /** Background Dart execution context. */
-  private static FlutterNativeView backgroundFlutterView;
+  private static FlutterEngine backgroundFlutterEngine;
 
   private static MethodChannel backgroundChannel;
 
@@ -63,12 +65,13 @@ public class FlutterFirebaseMessagingService extends FirebaseMessagingService {
 
   private static Context backgroundContext;
 
+  private static FirebaseMessagingPlugin firebaseMessagingPlugin;
+
   @Override
   public void onCreate() {
     super.onCreate();
 
     backgroundContext = getApplicationContext();
-    FlutterMain.ensureInitializationComplete(backgroundContext, null);
 
     // If background isolate is not running start it.
     if (!isIsolateRunning.get()) {
@@ -139,29 +142,35 @@ public void onNewToken(String token) {
    *     handling on the dart side.
    */
   public static void startBackgroundIsolate(Context context, long callbackHandle) {
-    FlutterMain.ensureInitializationComplete(context, null);
-    String appBundlePath = FlutterMain.findAppBundlePath();
-    FlutterCallbackInformation flutterCallback =
-        FlutterCallbackInformation.lookupCallbackInformation(callbackHandle);
-    if (flutterCallback == null) {
-      Log.e(TAG, "Fatal: failed to find callback");
+    if (backgroundFlutterEngine != null) {
+      Log.e(TAG, "Background isolate already started");
       return;
     }
 
-    // Note that we're passing `true` as the second argument to our
-    // FlutterNativeView constructor. This specifies the FlutterNativeView
-    // as a background view and does not create a drawing surface.
-    backgroundFlutterView = new FlutterNativeView(context, true);
-    if (appBundlePath != null) {
-      if (pluginRegistrantCallback == null) {
-        throw new RuntimeException("PluginRegistrantCallback is not set.");
+    String appBundlePath = FlutterMain.findAppBundlePath();
+    AssetManager assets = context.getAssets();
+    if (!isIsolateRunning.get()) {
+      backgroundFlutterEngine = new FlutterEngine(context);
+
+      // 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.
+      FlutterCallbackInformation flutterCallback =
+          FlutterCallbackInformation.lookupCallbackInformation(callbackHandle);
+
+      DartExecutor executor = backgroundFlutterEngine.getDartExecutor();
+      firebaseMessagingPlugin.initializeBackgroundMethodChannel(executor);
+      DartCallback dartCallback = new DartCallback(assets, appBundlePath, flutterCallback);
+
+      executor.executeDartCallback(dartCallback);
+
+      // The pluginRegistrantCallback should only be set in the V1 embedding as
+      // plugin registration is done via reflection in the V2 embedding.
+      // If set while using V2 embedding, the application will crash.
+      if (pluginRegistrantCallback != null) {
+        Log.d(TAG, "Proceeding with v1 embedding");
+        pluginRegistrantCallback.registerWith(new ShimPluginRegistry(backgroundFlutterEngine));
       }
-      FlutterRunArguments args = new FlutterRunArguments();
-      args.bundlePath = appBundlePath;
-      args.entrypoint = flutterCallback.callbackName;
-      args.libraryPath = flutterCallback.callbackLibraryPath;
-      backgroundFlutterView.runFromBundle(args);
-      pluginRegistrantCallback.registerWith(backgroundFlutterView.getPluginRegistry());
     }
   }
 
@@ -182,6 +191,16 @@ public static void onInitialized() {
     }
   }
 
+  /**
+   * Set the Firebase messaging plugin instance that is used to register method channels. This
+   * method is only called when the plugin registers.
+   *
+   * @param plugin Firebase messaging plugin instance.
+   */
+  public static void setFirebaseMessagingPlugin(FirebaseMessagingPlugin plugin) {
+    firebaseMessagingPlugin = plugin;
+  }
+
   /**
    * Set the method channel that is used for handling background messages. This method is only
    * called when the plugin registers.
@@ -290,6 +309,10 @@ private static void executeDartCallbackInBackgroundIsolate(
    * message handling is enabled.
    *
    * @param callback Application class which implements PluginRegistrantCallback.
+   *     <p>Note: this is only necessary for applications using the V1 engine embedding API as
+   *     plugins are automatically registered via reflection in the V2 engine embedding API. If not
+   *     set, messaging callbacks will not be able to utilize functionality from other plugins nor
+   *     the background message handler.
    */
   public static void setPluginRegistrant(PluginRegistry.PluginRegistrantCallback callback) {
     pluginRegistrantCallback = callback;

packages/firebase_messaging/pubspec.yaml

@@ -2,7 +2,8 @@ name: firebase_messaging
 description: Flutter plugin for Firebase Cloud Messaging, a cross-platform
   messaging solution that lets you reliably deliver messages on Android and iOS.
 homepage: https://github.com/FirebaseExtended/flutterfire/tree/master/packages/firebase_messaging
-version: 7.0.2
+version: 8.0.0
+
 
 flutter:
   plugin: