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Learn how to update state in React forms effectively, especially when dealing with nested components. Discover the correct approach to passing down state setters for optimal performance.
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This video is based on the question https://stackoverflow.com/q/72381510/ asked by the user 'jaumeserr' ( https://stackoverflow.com/u/5152123/ ) and on the answer https://stackoverflow.com/a/72382436/ provided by the user 'Enfield Li' ( https://stackoverflow.com/u/16648127/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Properly Update State in React Forms When Managing Nested Components

Managing state in React can be tricky, especially when it involves deeply nested components. Many developers face the challenge of updating state correctly in a scenario where data is handled several levels deep in the component hierarchy. If you've ever been uncertain about how to update state with forms that exist in nested components, this guide is for you.

The Problem: Unable to Update State

In the case presented, the user is working with a CitiesPage component that fetches and displays a list of cities. The CityCard component is responsible for presenting each city with options for editing and deleting, and finally, there's an EditCityForm component for updating city details.

After filling out the form and submitting it, one major question arises: How can we update the original state in CitiesPage to reflect the changes made in EditCityForm?

Understanding the Issue

The main problem stems from the fact that the cities state is defined at the CitiesPage level, while the updates are attempted to be managed at the EditCityForm level in isolation. The user attempts to hold updated data in a local state (updateCity), which doesn't inherently link back to the cities state.

Key Takeaway:

You need to update the cities state directly from the EditCityForm, rather than managing the updated values independently.

The Solution: Passing the State Setter

To solve this issue, we can use the setter function responsible for updating the state. This means passing down setCities() function from the CitiesPage all the way down to the EditCityForm. Let’s break down how we can achieve this.

Step 1: Pass the Setters Down the Component Tree

In CitiesPage: Update your component to include setCities as a prop when rendering CityCard.

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

In CityCard: Ensure that when rendering EditCityForm via a modal, you also pass down setCities.

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

In EditCityForm: Adjust your handleSubmit function to directly modify the cities state.

Step 2: Updating the Cities State

Here’s how the code would look after modifications:

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

Key Points to Remember

Pass the setCities function from CitiesPage down through CityCard to EditCityForm.

Within EditCityForm, directly update the cities array using the passed-down setter. This will reflect the changes on the main page automatically.

You no longer need the local state (updateCity), as all updates are handled directly through the shared state.

Conclusion

By following these steps, you can efficiently manage state across nested components in a React application. This pattern not only simplifies the management of state but also ensures that updates are immediately reflected in the UI, leading to a more fluid user experience.

Give it a try in your next project! Happy coding!