How to Trigger a useEffect from an External Function in React Native

Discover how to effectively refresh your message list in React Native using an external function to trigger the useEffect. Perfect for handling foreground notifications!
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This video is based on the question https://stackoverflow.com/q/67136287/ asked by the user 'Dave Dean' ( https://stackoverflow.com/u/11991191/ ) and on the answer https://stackoverflow.com/a/67136757/ provided by the user 'Kapobajza' ( https://stackoverflow.com/u/5049799/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Trigger a useEffect from an External Function in React Native

If you’re diving into the world of JavaScript and React Native, you might find yourself facing some interesting challenges. One common issue that developers run into is how to trigger a useEffect method from an external function in their application. Let's explore this in the context of dealing with notifications using Firebase Cloud Messaging (FCM).

Understanding the Problem

In this case, you have an application that listens for messages from FCM. When a message arrives while the app is in the foreground, it processes the message and displays a notification. However, the existing message list does not update automatically to reflect the new messages that arrive while the app is already running.

The useEffect hook in your app retrieves and updates the message list when the app starts, but doesn't refresh when new messages come in. You want to find a way to trigger the useEffect to run again whenever a new message comes in, ideally without running into issues such as creating multiple listeners.

The Solution

There are several methods to resolve this issue, but here we focus on a clean and effective way to manage the useEffect and the listeners.

Step 1: Setting Up the Listener

You can keep your existing foregroundMessageHandler, but the key step is to also add a listener directly in your HomeScreen component that will update the state whenever a new message is received.

Here’s a refined solution:

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

Step 2: Modifying the Message Handling Logic

We modified the onMessage() listener to directly update the data state, appending new messages as they come in. This way, the FlatList component re-renders automatically without needing a second useEffect or triggering unnecessary re-fetches.

Key Considerations

Cleanup Listeners: Always ensure that your listeners are properly cleaned up when the component unmounts. This prevents memory leaks and duplicate operations.

State Management: By using the functional update form of setData, you ensure you always append messages based on the most recent state.

AsyncStorage Attention: While you are appending new messages in state, remember to also consider how you're managing messages in AsyncStorage if you need them to persist across app sessions.

Conclusion

By incorporating an FCM message listener directly in your HomeScreen component and updating the state upon receiving new messages, you can effectively refresh your message list without re-triggering the initial fetch.

This solution brings together both clarity and functionality, allowing your React Native application to handle incoming messages seamlessly.

Feel free to modify the handling functions and render logic per your specific application needs, but maintain the pattern of listening, handling, and state updating!

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