feat(messaging): add FID registration APIs

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

@@ -71,6 +71,12 @@ public class FlutterFirebaseMessagingPlugin
   private Observer<RemoteMessage> remoteMessageObserver;
   private final LiveData<String> liveDataToken = FlutterFirebaseTokenLiveData.getInstance();
   private Observer<String> tokenObserver;
+  private final LiveData<String> liveDataRegistered =
+      FlutterFirebaseRegisteredLiveData.getInstance();
+  private Observer<String> registeredObserver;
+  private final LiveData<String> liveDataUnregistered =
+      FlutterFirebaseUnregisteredLiveData.getInstance();
+  private Observer<String> unregisteredObserver;
 
   private RemoteMessage initialMessage;
   // We store the initial notification in a separate variable
@@ -93,10 +99,14 @@ private void initInstance(BinaryMessenger messenger) {
           channel.invokeMethod("Messaging#onMessage", content);
         };
     tokenObserver = token -> channel.invokeMethod("Messaging#onTokenRefresh", token);
+    registeredObserver = fid -> channel.invokeMethod("Messaging#onRegistered", fid);
+    unregisteredObserver = fid -> channel.invokeMethod("Messaging#onUnregistered", fid);
     // We remove these observers in the onDetachedFromEngine method. Using "observeForever()"
     // allows us to use without a LifecycleOwner.
     liveDataRemoteMessage.observeForever(remoteMessageObserver);
     liveDataToken.observeForever(tokenObserver);
+    liveDataRegistered.observeForever(registeredObserver);
+    liveDataUnregistered.observeForever(unregisteredObserver);
 
     registerPlugin(channelName, this);
   }
@@ -111,6 +121,8 @@ public void onAttachedToEngine(FlutterPluginBinding binding) {
   public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {
     liveDataToken.removeObserver(tokenObserver);
     liveDataRemoteMessage.removeObserver(remoteMessageObserver);
+    liveDataRegistered.removeObserver(registeredObserver);
+    liveDataUnregistered.removeObserver(unregisteredObserver);
   }
 
   @Override
@@ -184,6 +196,38 @@ private Task<Map<String, Object>> getToken() {
     return taskCompletionSource.getTask();
   }
 
+  private Task<Void> register() {
+    TaskCompletionSource<Void> taskCompletionSource = new TaskCompletionSource<>();
+
+    cachedThreadPool.execute(
+        () -> {
+          try {
+            Tasks.await(FirebaseMessaging.getInstance().register());
+            taskCompletionSource.setResult(null);
+          } catch (Exception e) {
+            taskCompletionSource.setException(e);
+          }
+        });
+
+    return taskCompletionSource.getTask();
+  }
+
+  private Task<Void> unregister() {
+    TaskCompletionSource<Void> taskCompletionSource = new TaskCompletionSource<>();
+
+    cachedThreadPool.execute(
+        () -> {
+          try {
+            Tasks.await(FirebaseMessaging.getInstance().unregister());
+            taskCompletionSource.setResult(null);
+          } catch (Exception e) {
+            taskCompletionSource.setException(e);
+          }
+        });
+
+    return taskCompletionSource.getTask();
+  }
+
   private Task<Void> subscribeToTopic(Map<String, Object> arguments) {
     TaskCompletionSource<Void> taskCompletionSource = new TaskCompletionSource<>();
 
@@ -567,6 +611,12 @@ public void onMethodCall(final MethodCall call, @NonNull final Result result) {
       case "Messaging#getToken":
         methodCallTask = getToken();
         break;
+      case "Messaging#register":
+        methodCallTask = register();
+        break;
+      case "Messaging#unregister":
+        methodCallTask = unregister();
+        break;
       case "Messaging#subscribeToTopic":
         methodCallTask = subscribeToTopic(call.arguments());
         break;

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

@@ -14,6 +14,16 @@ public void onNewToken(@NonNull String token) {
     FlutterFirebaseTokenLiveData.getInstance().postToken(token);
   }
 
+  @Override
+  public void onRegistered(@NonNull String installationId) {
+    FlutterFirebaseRegisteredLiveData.getInstance().postFid(installationId);
+  }
+
+  @Override
+  public void onUnregistered(@NonNull String installationId) {
+    FlutterFirebaseUnregisteredLiveData.getInstance().postFid(installationId);
+  }
+
   @Override
   public void onMessageReceived(@NonNull RemoteMessage remoteMessage) {
     // Added for commenting purposes;

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

@@ -0,0 +1,22 @@
+// Copyright 2026 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package io.flutter.plugins.firebase.messaging;
+
+import androidx.lifecycle.LiveData;
+
+public class FlutterFirebaseRegisteredLiveData extends LiveData<String> {
+  private static FlutterFirebaseRegisteredLiveData instance;
+
+  public static FlutterFirebaseRegisteredLiveData getInstance() {
+    if (instance == null) {
+      instance = new FlutterFirebaseRegisteredLiveData();
+    }
+    return instance;
+  }
+
+  public void postFid(String fid) {
+    postValue(fid);
+  }
+}

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

@@ -0,0 +1,22 @@
+// Copyright 2026 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package io.flutter.plugins.firebase.messaging;
+
+import androidx.lifecycle.LiveData;
+
+public class FlutterFirebaseUnregisteredLiveData extends LiveData<String> {
+  private static FlutterFirebaseUnregisteredLiveData instance;
+
+  public static FlutterFirebaseUnregisteredLiveData getInstance() {
+    if (instance == null) {
+      instance = new FlutterFirebaseUnregisteredLiveData();
+    }
+    return instance;
+  }
+
+  public void postFid(String fid) {
+    postValue(fid);
+  }
+}

packages/firebase_messaging/firebase_messaging/example/android/app/src/main/AndroidManifest.xml

@@ -30,6 +30,9 @@
         <meta-data
             android:name="flutterEmbedding"
             android:value="2" />
+        <meta-data
+            android:name="firebase_messaging_installation_id_enabled"
+            android:value="true" />
     </application>
     <!-- Required to query activities that can process text, see:
          https://developer.android.com/training/package-visibility and

packages/firebase_messaging/firebase_messaging/example/integration_test/e2e_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// ignore_for_file: deprecated_member_use
+
 import 'dart:async';
 
 import 'package:firebase_core/firebase_core.dart';
@@ -285,6 +287,79 @@ void main() {
         ); // only run for manual testing
       });
 
+      group('register()', () {
+        test(
+          'emits a FID through onRegistered',
+          () async {
+            final completer = Completer<String>();
+            late StreamSubscription<String> subscription;
+
+            subscription = messaging.onRegistered.listen((fid) {
+              if (!completer.isCompleted) {
+                completer.complete(fid);
+              }
+            });
+
+            await messaging.register();
+
+            final fid = await completer.future.timeout(
+              const Duration(seconds: 30),
+            );
+            expect(fid, isNotEmpty);
+
+            await subscription.cancel();
+          },
+          // iOS CI does not have the push/APNs setup needed for FID registration.
+          skip: kIsWeb ||
+              (defaultTargetPlatform == TargetPlatform.iOS && skipTestsOnCI) ||
+              (defaultTargetPlatform != TargetPlatform.android &&
+                  defaultTargetPlatform != TargetPlatform.iOS),
+        );
+      });
+
+      group('unregister()', () {
+        test(
+          'emits the unregistered FID through onUnregistered',
+          () async {
+            final registeredCompleter = Completer<String>();
+            final unregisteredCompleter = Completer<String>();
+
+            final registeredSubscription = messaging.onRegistered.listen((fid) {
+              if (!registeredCompleter.isCompleted) {
+                registeredCompleter.complete(fid);
+              }
+            });
+            final unregisteredSubscription =
+                messaging.onUnregistered.listen((fid) {
+              if (!unregisteredCompleter.isCompleted) {
+                unregisteredCompleter.complete(fid);
+              }
+            });
+
+            await messaging.register();
+            final registeredFid = await registeredCompleter.future.timeout(
+              const Duration(seconds: 30),
+            );
+
+            await messaging.unregister();
+            final unregisteredFid = await unregisteredCompleter.future.timeout(
+              const Duration(seconds: 30),
+            );
+
+            expect(registeredFid, isNotEmpty);
+            expect(unregisteredFid, registeredFid);
+
+            await registeredSubscription.cancel();
+            await unregisteredSubscription.cancel();
+          },
+          // iOS CI does not have the push/APNs setup needed for FID registration.
+          skip: kIsWeb ||
+              (defaultTargetPlatform == TargetPlatform.iOS && skipTestsOnCI) ||
+              (defaultTargetPlatform != TargetPlatform.android &&
+                  defaultTargetPlatform != TargetPlatform.iOS),
+        );
+      });
+
       group('subscribeToTopic()', () {
         test(
           'successfully subscribes from topic',

packages/firebase_messaging/firebase_messaging/example/ios/Runner/Info.plist

@@ -20,6 +20,8 @@
 	<string>????</string>
 	<key>CFBundleVersion</key>
 	<string>$(FLUTTER_BUILD_NUMBER)</string>
+	<key>FirebaseMessagingInstallationIdEnabled</key>
+	<true/>
 	<key>LSRequiresIPhoneOS</key>
 	<true/>
 	<key>UIBackgroundModes</key>