Скачать или смотреть How to Properly Update a Tile in ListView.builder Using BLoC in Flutter

Learn how to effectively manage state in Flutter's `ListView.builder` using BLoC. Discover how to update individual tiles without affecting the entire list.
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This video is based on the question https://stackoverflow.com/q/75798192/ asked by the user 'Ayan Dasgupta' ( https://stackoverflow.com/u/19413610/ ) and on the answer https://stackoverflow.com/a/75798497/ provided by the user 'Md. Yeasin Sheikh' ( https://stackoverflow.com/u/10157127/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Managing State with BLoC in Flutter: Updating Individual Items in a ListView

When developing applications in Flutter, it's common to use a ListView.builder for displaying dynamic lists of items. However, managing the state of individual items in such a list can often lead to issues, especially when implementing state management solutions like BLoC. In this post, we will address a common problem encountered while toggling the state of list items and provide an efficient solution.

The Problem

Imagine you have a ListView.builder that displays multiple tiles, each containing text and an icon. When the icon is tapped, you want to toggle the text font between bold and normal as well as change the icon from "read" to "unread." However, an issue arises: tapping on one tile causes all tiles to be updated at once, rather than just the tile that was tapped.

The current implementation, while functional, rebuilds the entire list instead of just the modified tile due to the way the state is managed. This can lead to performance issues and a poor user experience.

Understanding the Current Implementation

Here’s a quick rundown of the current implementation:

Tile State Management: Currently, there are two states (UnreadState and ReadState), which manage the states of the tiles.

Single Event: There are separate events for toggling between states (UnreadEvent and ReadEvent).

ListView.builder: The ListView.builder rebuilds entire tiles based on the global state rather than the individual tile's state, which is inefficient.

Current Code Snippet

Here's a simplified snippet of the code currently being used for the TileBloc:

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

The Solution: Using a Model Class and a Single Event

To resolve the issue of updating individual tiles within the ListView.builder, we need to refactor our state management:

Step 1: Create a Model Class

Start by creating a new Item class to represent each tile. This class will hold the message and the read status.

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

Step 2: Update Tile Events

Revise the events to include a ToggleRead event, capable of toggling between read and unread states for a specific item.

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

Step 3: Refactor Tile State

Modify the TileState to hold a list of items, which allows us to track the state of each tile independently.

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

Step 4: Update TileBloc Logic

Now, we can update the TileBloc to handle the toggling logic for an individual item based on the state.

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

Step 5: Integrate All Changes in the UI

Finally, ensure your UI leverages the updated bloc and seamlessly rebuilds only the modified tile.

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

Conclusion

By implementing a model class for the tiles and restructuring how we handle events and states, we can effectively manage updates to the ListView.builder in Flutter using BLoC. This not only ensures that only the intended tile updates, but it also greatly enhances the performance and user experience of your application.

With this approach, you can maintain clear, independent states for your list items, leading to a scalable and maintainable codebase.