Скачать или смотреть How to Properly Reinitialize Your Bloc in Flutter After Navigating Back from Another Screen

Learn how to effectively call `initState` or `didChangeDependencies` in Flutter when popping back to a screen, ensuring your Bloc is correctly reinitialized without errors.
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This video is based on the question https://stackoverflow.com/q/63524224/ asked by the user 'kokoko' ( https://stackoverflow.com/u/4862911/ ) and on the answer https://stackoverflow.com/a/63524938/ provided by the user 'alireza easazade' ( https://stackoverflow.com/u/6748763/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Properly Reinitialize Your Bloc in Flutter After Navigating Back from Another Screen

Navigating between screens in a Flutter application is a common practice, but it can lead to some complications, especially when using the Bloc design pattern. One frequent issue developers face is reinitializing their Bloc after returning to a previous screen. This situation often arises after a screen is popped from the navigation stack, and the screen you're returning to encounters errors like "Bad state: Cannot add new events after calling close."

The Problem

In a typical Flutter application that uses the Bloc pattern, each screen may have its own Bloc instance. When you navigate away from a screen (for instance, from screen 1 to screen 2), the dispose method is triggered in the first screen, leading to the closure of its associated Bloc. Upon returning to screen 1 from screen 2, you may want to reinitialize your Bloc to avoid accessing an already closed stream.

Here’s what you need to tackle:

Upon navigating back, the previous screen should be able to re-initialize the Bloc.

Avoid experiencing the error message that occurs when trying to add new events after the Bloc has been closed.

The Solution

To solve this issue, the recommended approach is to reinitialize your Bloc when you return from the second screen. This can be achieved conveniently in Flutter using the Navigator class and its result callback. Let's walk through the steps to reinitialize your Bloc.

Step-by-step Breakdown

Using the Navigator to Push to the Second Screen:
You need to ensure that you wait for a result when you push to the next screen. This can be done by using the then method, which accepts a callback that runs once the screen has been popped.

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Reinitializing the Bloc:
Inside the result callback, you can safely create a new instance of your Bloc. This guarantees that every time you pop back to the previous screen, the Bloc is reinitialized, ensuring that it is ready to accept events once again.

Conclusion

By implementing this method, you ensure that your Bloc is properly reinitialized each time you navigate back to a screen in your Flutter application. This practice not only prevents the "Bad state: Cannot add new events after calling close" error but also keeps your app's architecture clean and manageable.

Now you can navigate between your screens seamlessly while maintaining the functionality of your Bloc instances! Happy coding!