Скачать или смотреть Solving the NoSuchMethodError in Flutter: A Guide to Properly Handling FCM Notifications

Learn how to fix the error "The method '+ ' was called on null" when using Firebase Cloud Messaging (FCM) in Flutter. This guide guides you step-by-step through your notification handling logic.
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Solving the NoSuchMethodError in Flutter: A Guide to Properly Handling FCM Notifications

If you're developing a Flutter app that uses Firebase Cloud Messaging (FCM) for push notifications, you might encounter a frustrating error: "NoSuchMethodError: The method '+ ' was called on null". This usually happens when some expected data is missing from your notification payload, especially when the app is launched from a terminated state.

In this guide, we'll delve into the reasons for this error and explore the solution to ensure your application displays notifications correctly, even when it has been killed or inactive.

Understanding the Error

The error occurs due to an attempt to concatenate a null string with another string in the following line from your onLaunch handler:

[[See Video to Reveal this Text or Code Snippet]]

If item_description is not present in the notification data sent from your server when the app is launched from a terminated state, Flutter throws the error as null cannot be concatenated with another string.

How to Fix the Issue

Step 1: Review Your Notification Payload

Before diving into code fixes, ensure that your server sends the required data in the FCM notification payload. For example, check that it includes keys like item_description, item_title, etc.

Step 2: Safely Access Notification Data

To avoid null errors, you need to safely access the attributes in your notification data. Here’s how to do that:

Update the onLaunch Handler

When handling messages, always check if the data exists before accessing it. Modify your onLaunch method as follows:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Implement Error Handling

Using conditional checks to wrap your data accesses helps in preventing runtime exceptions. Here’s a full example integrating these principles:

[[See Video to Reveal this Text or Code Snippet]]

Step 4: Test Your Changes

After making these changes, it's essential to test your app. Kill the app, send a push notification, and observe whether it now correctly shows your dialog with the notification details.

Conclusion

Handling notifications in a Flutter application using FCM requires careful attention to the data you receive. By ensuring that you check for null values and handle notifications properly, you can avoid common pitfalls like NoSuchMethodError.

Implement the outlined strategies to enhance your app’s resilience when interacting with FCM, providing users with a smooth experience every time they receive a push notification.

Take Action!

Have you faced this issue in your Flutter application? Try the solutions discussed in this article and share your experiences in the comments!