Firebase Cloud Messaging (FCM) is a powerful tool for sending push notifications to your app users, enabling real-time updates and engagement. However, a common challenge developers face is the infamous “onMessageReceived not called when app in background” issue. This frustrating problem can significantly impact the reliability of your notification system, leaving users unaware of important updates. This article delves into the reasons behind this issue, providing practical solutions and best practices to ensure your FCM notifications are delivered reliably, regardless of your app’s state.

Understanding the onMessageReceived Method

The onMessageReceived() method is the heart of FCM’s client-side handling. When your app is in the foreground, this method is called whenever a new notification arrives. It allows you to process the notification data and display a custom notification to the user. However, the behavior changes when the app is in the background or killed. Understanding this difference is crucial to troubleshooting notification delivery issues.

When your app is in the background, the system handles the notification display by default, showing a basic notification in the system tray. This default behavior often leads to the misconception that onMessageReceived() isn’t called, but the reality is more nuanced.

Why onMessageReceived Isn’t Called (Always) in the Background

The behavior of onMessageReceived() is heavily influenced by the type of notification payload received: notification messages and data messages. Notification messages, containing predefined keys like title and body, are handled directly by the FCM SDK and system. This means onMessageReceived() is typically not invoked for these messages when your app is in the background, as the system takes care of displaying the notification. Data messages, on the other hand, are meant for custom handling within your app. Even when your app is in the background, onMessageReceived() is called to allow you to process the data and decide how to handle the notification. This distinction is often the source of confusion and the root cause of many notification delivery issues.

Another factor affecting notification delivery is the device’s Doze mode, introduced in Android 6.0 (Marshmallow). Doze mode aims to conserve battery life by restricting background app activity. While essential for battery optimization, it can interfere with the timely delivery of FCM notifications. Understanding how Doze mode interacts with FCM is vital for ensuring reliable notification delivery.

Ensuring Reliable Notification Delivery

To ensure your notifications reach users regardless of app state, structure your payloads as data messages. This ensures onMessageReceived() is called even when your app is in the background, giving you full control over notification handling. Here’s how to structure a data message:

{ "to": "your_fcm_token", "data": { "title": "Your Notification Title", "body": "Your Notification Body", "custom_key": "Custom Value" } } 

Include other relevant key-value pairs within the data payload to pass additional information to your app. Within onMessageReceived(), you can then process this data and create a custom notification using the NotificationCompat.Builder.

• Always use data messages for reliable background notification delivery.
• Handle notification display and logic within onMessageReceived().

Handling Doze Mode and Background Restrictions

Doze mode and background restrictions can significantly impact the timely delivery of notifications. To mitigate this, use high-priority FCM messages for critical notifications that require immediate delivery. For less urgent notifications, consider scheduling them using the FCM scheduling features. Additionally, prompt users to whitelist your app from battery optimization settings to ensure uninterrupted notification delivery. “According to a 2023 study, 70% of users disable notifications due to excessive or irrelevant alerts,” highlighting the importance of thoughtful notification management.

Here’s how to set the priority of an FCM message:

{ "to": "your_fcm_token", "priority": "high", "data": { // Your data payload } } 

1. Use high-priority messages for critical notifications.
2. Schedule non-urgent notifications.
3. Encourage users to whitelist your app from battery optimizations.

Place infographic about different message types and their behavior here.

Testing and Debugging

Thorough testing is essential to verify that your FCM implementation works reliably across different scenarios. Test with the app in the foreground, background, and killed states. Use a physical device for testing, as emulators might not accurately represent real-world behavior, especially regarding background restrictions. Tools like the Firebase console and adb logs can help debug notification delivery issues. Leverage these resources to identify and resolve any problems quickly. You can learn more about FCM best practices from the official Firebase documentation.

For additional insights into Android background processing, check out this helpful article on Background Processing. Understanding background processes and restrictions is crucial for optimizing notification delivery.

• Test on physical devices for realistic results.
• Use Firebase console and adb logs for debugging.

By implementing these strategies and thoroughly testing your implementation, you can ensure that your FCM notifications reach your users reliably, enhancing engagement and delivering a seamless user experience. This information empowers you to tackle the common challenges of FCM notification delivery. Remember to test your implementation thoroughly to ensure consistent performance across various device and app states. Don’t let background restrictions silence your crucial updates. Take control of your FCM notifications today by applying the techniques outlined in this guide. Learn more about Android’s battery optimization strategies here and fine-tune your app’s behavior accordingly. Consider exploring topics like advanced FCM features, notification customization, and user segmentation to maximize the impact of your messaging strategy.

Frequently Asked Questions

Q: Why am I not receiving notifications when my app is closed?

A: This likely occurs because the system handles notification messages when the app is closed or in the background. Use data messages to ensure onMessageReceived() is always called.

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Question & Answer :
I’m working with Firebase and testing sending notifications to my app from my server while the app is in the background. The notification is sent successfully, it even appears on the notification centre of the device, but when the notification appears or even if I click on it, the onMessageReceived method inside my FCMessagingService is never called.

When I tested this while my app was in the foreground, the onMessageReceived method was called and everything worked fine. The problem occurs when the app is running in the background.

Is this intended behaviour, or is there a way I can fix this?

Here is my FBMessagingService:

import android.util.Log; import com.google.firebase.messaging.FirebaseMessagingService; import com.google.firebase.messaging.RemoteMessage; public class FBMessagingService extends FirebaseMessagingService { @Override public void onMessageReceived(RemoteMessage remoteMessage) { Log.i("PVL", "MESSAGE RECEIVED!!"); if (remoteMessage.getNotification().getBody() != null) { Log.i("PVL", "RECEIVED MESSAGE: " + remoteMessage.getNotification().getBody()); } else { Log.i("PVL", "RECEIVED MESSAGE: " + remoteMessage.getData().get("message")); } } } 

This is working as intended, notification messages are delivered to your onMessageReceived callback only when your app is in the foreground. If your app is in the background or closed then a notification message is shown in the notification center, and any data from that message is passed to the intent that is launched as a result of the user tapping on the notification.

You can specify a click_action in your JSON to indicate the intent that should be launched when the notification is tapped by the user. The main activity is used if no click_action is specified.

When the intent is launched you can use the

getIntent().getExtras(); 

to retrieve a Set that would include any data sent along with the notification message.

For more on notification message see docs.