How to Trigger Bloc Event Again in Flutter After Navigating Back

Learn how to effectively trigger a `Bloc` event again in Flutter when navigating between screens. Discover solutions for proper state management and dependency injection issues.
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This video is based on the question https://stackoverflow.com/q/70078308/ asked by the user 'Akila Ishan' ( https://stackoverflow.com/u/12722013/ ) and on the answer https://stackoverflow.com/a/70120369/ provided by the user 'Akila Ishan' ( https://stackoverflow.com/u/12722013/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Trigger Bloc Event Again in Flutter After Navigating Back

Navigating in Flutter apps often involves managing application state, especially when using the BLoC pattern for state management. A common issue that developers face is the prevention of certain events from being triggered after navigation. In this guide, we will discuss the specific problem of not being able to trigger a SubmitDataEvent() again when coming back to a previous screen and provide a clear solution in a structured way.

The Problem Scenario

Imagine you have two screens in your Flutter application:

First Screen: Where users fill out a form and submit data by triggering a SubmitDataEvent().

Second Screen: The screen that appears after successful data submission.

Here’s What Happens:

After filling the form on the first screen and hitting the next button, the event - SubmitDataEvent() is successfully added to the block and leads to a SuccessState.

Navigating back from the second screen to the first does not reset the state, so when you update the input and try to submit again, the event does not trigger.

This issue arises because the existing state remains as SuccessState, leading to confusion in event handling.

Understanding State Management with BLoC

In the BLoC (Business Logic Component) pattern, state management typically depends on the internal instances of the BLoC. In this case, your BLoC may not reset properly because of how the dependency injection is handled when navigating back to the first screen.

Key Points:

State Persistence: The state persists due to the BLoC instance not being re-initialized when returning to the screen.

Dependency Injection: Using a dependency injection framework (like GetIt or Provider), the BLoC is created only once, which can cause issues when navigating back.

Solution to Trigger BLoC Event Again

Let’s walk through the solution step-by-step. The solution revolves around resetting the BLoC instance so it can re-trigger the event when users return to the first screen.

Step 1: Resetting the BLoC Instance

Modify your dispose() method in the first screen class to reset the BLoC instance as follows:

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

The line injection.resetLazySingleton<SubmitPersonalDetailsBloc>() ensures that a new instance of the BLoC is created on each navigation.

Step 2: Handling State Changes

Make sure your BLoC is designed to handle state changes when it is re-initialized.

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

This will ensure that whenever you navigate back to this screen, a fresh instance of your BLoC is utilized, enabling it to handle events as new inputs are given.

Conclusion

Handling state management effectively in Flutter, especially when using the BLoC pattern, can be tricky, particularly with navigation. By resetting your BLoC instance whenever returning to a screen, you can ensure that all processes within the BLoC can run again, allowing your application to respond correctly to user interactions.

Final Thoughts

Navigating effectively between screens while maintaining the integrity of your application's state is essential. By understanding the core concepts of state management and applying techniques like resetting your BLoC instance, you can enhance user experience and application functionality.

If you have any questions or need further clarification, feel free to drop them in the comments below!

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