Added FID-based registration snippets for FCM

messaging/app/src/main/java/com/google/firebase/example/messaging/MyFirebaseMessagingService.java

@@ -136,4 +136,40 @@ public Result doWork() {
             return Result.success();
         }
     }
+
+    private void registerFid() {
+        // [START register_fid]
+        // Trigger manual registration if auto-initialization is turned off.
+        // Consider calling this every time the app starts to guarantee sync status.
+        FirebaseMessaging.getInstance().register()
+            .addOnCompleteListener(task -> {
+                if (!task.isSuccessful()) {
+                    // Registration failed. Consider retrying the registration with exponential backoff.
+                    Log.w(TAG, "Failed to register with Firebase Cloud Messaging", task.getException());
+                }
+                // Success! The Firebase Installation ID can be used to target messages to this app
+                // instance and will be delivered asynchronously to your onRegistered() callback.
+            });
+        // [END register_fid]
+    }
+
+    // [START on_fid_registered]
+    /**
+     * There are three scenarios when `onRegistered` is called:
+     * 1) Every time a manual `register()` call finishes successfully
+     * 2) Whenever the FID is changed and the app is re-registered with FCM via the new FID
+     * 3) Automatically on app startup or routine sync when auto-initialization is enabled.
+     * Under #2, there are three scenarios when the existing FID is changed:
+     * A) App is restored to a new device
+     * B) User uninstalls/reinstalls the app
+     * C) User clears app data
+     */
+    @Override
+    public void onRegistered(@NonNull String installationId) {
+        Log.d(TAG, "Registered installation ID: " + installationId);
+
+        // Send the Firebase Installation ID to your app server.
+        sendRegistrationToServer(installationId);
+    }
+    // [END on_fid_registered]
 }

messaging/app/src/main/java/com/google/firebase/example/messaging/kotlin/MyFirebaseMessagingService.kt

@@ -133,4 +133,38 @@ class MyFirebaseMessagingService : FirebaseMessagingService() {
             return Result.success()
         }
     }
+
+    private fun registerFid() {
+        // [START register_fid]
+        // Trigger manual registration if auto-initialization is turned off.
+        // Consider calling this every time the app starts to guarantee sync status.
+        FirebaseMessaging.getInstance().register()
+            .addOnCompleteListener { task ->
+                if (!task.isSuccessful()) {
+                    Log.w(TAG, "Failed to register with Firebase Cloud Messaging", task.exception)
+                }
+                // Success! The Firebase Installation ID can be used to target messages to this app
+                // instance and will be delivered asynchronously to your onRegistered() callback.
+            }
+    }
+    // [END register_fid]
+
+    // [START on_fid_registered]
+    /**
+     * There are three scenarios when `onRegistered` is called:
+     * 1) Every time a manual `register()` call finishes successfully
+     * 2) Whenever the FID is changed and the app is re-registered with FCM via the new FID.
+     * 3) Automatically on app startup or routine sync when auto-initialization is enabled.
+     * Under #2, there are three scenarios when the existing FID is changed:
+     * A) App is restored to a new device
+     * B) User uninstalls/reinstalls the app
+     * C) User clears app data
+     */
+    override fun onRegistered(installationId: String) {
+        Log.d(TAG, "Registered installation ID: $installationId")
+
+        // Send the Firebase Installation ID to your app server.
+        sendRegistrationToServer(installationId)
+    }
+    // [END on_fid_registered]
 }