How to Listen to BLoC Events From Another Screen in Flutter

Discover how to effectively listen to BLoC events from multiple screens in Flutter applications and manage state efficiently when navigating.
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How to Listen to BLoC Events From Another Screen in Flutter

Flutter applications often require communication between different screens or parts of the app. This means keeping data in sync, especially when navigating back and forth. If you are using the BLoC (Business Logic Component) pattern, you may encounter a common problem: how do you listen to events from one screen after navigating back from another? This guide will take you through a real-world problem and its solution step-by-step.

The Problem

In my Flutter application, I have two screens:

Products Screen: Displays a list of products each wrapped in a CheckboxListTile that shows whether each product is checked or not based on a list of selected items.

Cart Screen: Holds the selected products from the products screen and allows users to remove items from their cart using a Dismissible widget.

The requirement is straightforward: After removing an item from the cart and returning to the products screen by pressing the back button, the checkbox of the removed product should update to unchecked. This is because its ID is no longer in the selectedItemsList. However, the issue arises when the checkbox remains checked due to the state not updating correctly when returning to the products screen.

The Solution

To solve this problem, we need to ensure that the app listens correctly to BLoC events even when navigating between screens. Here’s a detailed breakdown of the steps to achieve this:

1. Understanding BLoC and State Management

The first step is grasping the BLoC framework's way of handling states and events. When components (screens) in a Flutter application use BLoC, we can emit events that other components listen to.

2. Emit Event on Item Dismiss

When an item is removed from the cart, we need to trigger a specific BLoC event. In this case, it would be RemoveItemFromCart. Here's the code that handles this event:

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

This snippet adds the removal of an item to the event stream of the CartBloc.

3. Yielding State After Item Removal

Next, we need to yield a new state called ItemRemovedFromCart once the event has been processed in the BLoC. This new state will reflect the current items in the cart:

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

4. Listening for State Changes in Products Screen

On the products screen, we utilize a BlocBuilder to listen for states emitted by the BLoC. If the state is ItemRemovedFromCart, we will trigger the rebuild of the products list. Here’s how you implement this in your code:

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

5. Make Sure BLoC Remains Open

The final piece of the puzzle is ensuring that the BLoC instance persists while navigating across screens, hence keeping the listener active. When using BlocProvider, be mindful not to close the BLoC prematurely.

Conclusion

By following the above steps, you can effectively listen to BLoC events from multiple screens in your Flutter application. This allows for smoother interactions and real-time updates to the UI as the state changes, ensuring that your users have a seamless experience.

If you have any further questions or need additional help, feel free to ask! Happy coding!

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