How to Pre-fill a TextField with BLoC in Flutter

Discover how to efficiently pre-fill a TextField using BLoC in Flutter without losing editability. Learn the step-by-step solution to overcome the challenge.
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This video is based on the question https://stackoverflow.com/q/66295377/ asked by the user 'user54517' ( https://stackoverflow.com/u/3897426/ ) and on the answer https://stackoverflow.com/a/66295433/ provided by the user 'YoBo' ( https://stackoverflow.com/u/14513938/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Efficiently Pre-fill a TextField with BLoC in Flutter

Creating forms in Flutter for tasks like posting or editing ads is a common requirement. However, a significant challenge often arises when trying to pre-fill a field while still allowing users to modify it. This guide addresses a typical scenario: pre-filling a TextField for ad editing without losing the text editability due to the user's input and Flutter's rebuilding process.

The Problem: Ad Editing with Pre-filled Fields

If you're working on a Flutter application and using the BLoC (Business Logic Component) pattern to manage your app's logic, you may have faced the following issue:

When users navigate to the ad editing screen, you want to pre-fill the TextField with the existing ad content.

The challenge is that, as the content of the field changes, the TextField is rebuilt, which also rebuilds the associated TextEditingController.

This rebuilding prevents you from pre-filling the field appropriately without losing the ability to edit.

Here's an example of what the problem looks like in code:

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

In this structure, the TextEditingController is reinitialized every time the TextField rebuilds, thus negating the user's ability to edit what they've attempted to fill in.

The Solution: Using TextFormField with initialValue

The solution to this problem lies in rethinking the way you set up your TextField. Instead of using TextField with a controller, you should use TextFormField and leverage the initialValue property.

Step-by-Step Implementation

Change to TextFormField

Switch from TextField to TextFormField, which allows you to set an initial value that is only rendered once.

Update the Code

Modify your code to utilize initialValue instead of a TextEditingController. Here's the revised code:

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

Key Benefits

State Persistence: By using initialValue, you preserve the ability to edit the text without it being overridden on each rebuild.

Simplified Code: This approach removes the need for a manual controller, leading to cleaner, more maintainable code.

User Experience: Users can easily see and edit the existing ad details without frustrating interruptions.

Conclusion

The process of pre-filling a TextField for editing ad content while using BLoC in Flutter can be streamlined by utilizing TextFormField with the initialValue parameter. This adjustment not only solves the rebuilding issue but also enhances the overall user experience in your app.

By adopting this approach, you ensure that your forms work as intended, enabling users to edit pre-filled data seamlessly. Happy coding!

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