Скачать или смотреть Resolving the setState Issue in Flutter: Managing State with TextFormField

Discover how to properly manage state in Flutter when using `TextFormField`. Learn about keeping `GlobalKey` as a state variable to eliminate focus loss and ensure smooth UI updates.
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This video is based on the question https://stackoverflow.com/q/75569367/ asked by the user 'Shobi' ( https://stackoverflow.com/u/2693543/ ) and on the answer https://stackoverflow.com/a/75569680/ provided by the user 'Alex Sunder Singh' ( https://stackoverflow.com/u/7997083/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving the setState Issue in Flutter: Managing State with TextFormField

Managing state in Flutter can sometimes be a challenge, especially for beginners. A common problem arises when using TextFormField to collect user inputs while trying to update the state using the setState method. This article will address a specific issue that many developers face: calling setState in the onChanged callback of a TextFormField, which causes the text field to lose focus. Let's break it down and see how to resolve it.

The Problem

Suppose you have a TextFormField, and you want to update a state variable when the text changes. Here is a snippet where this is attempted:

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

The developer has set up an onChanged callback that updates _tag and calls setState() to refresh the UI. However, an issue arises where the text field loses focus and does not display the entered characters properly. This happens due to the fact that the _formKey is created inside the build method.

The Solution

1. Move GlobalKey Declaration to State Variable

To resolve this issue, you should declare _formKey as a state variable instead of a local variable within the build method. By doing this, the same instance of the Form is maintained even after state updates, which helps to preserve the text field's state and focus.

Here's how you can refactor the code correctly:

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

2. Explanation of Changes

Consistency in State: By making sure _formKey is a state variable, we ensure that its state is preserved across re-renders caused by setState().

Improved UX: This prevents the text field from losing focus when the state updates, leading to a smoother user experience.

Conclusion

Managing state in Flutter, especially with forms, is crucial for ensuring a seamless experience. By following the solution provided, you can effectively use TextFormField without experiencing focus issues or unexpected behavior. Always remember to keep your form keys as state variables to avoid unnecessary reinitialization and maintain the UI state you need.

By applying these best practices, you will find your Flutter development smoother and much more enjoyable.