表單和受控組件

In React, forms and controlled components are essential for managing form data efficiently. A controlled component is a component that does not maintain its own state for input fields but instead receives its current value and change handler as props. This allows you to have a single source of truth for the form data, making it easier to manage.

Basic Example of a Controlled Component

Here’s a simple example of how to create a controlled component in a React functional component:

import React, { useState } from 'react';

const MyForm = () => {
  const [formData, setFormData] = useState({
    name: '',
    email: '',
  });

  const handleChange = (event) => {
    const { name, value } = event.target;
    setFormData((prevData) => ({
      ...prevData,
      [name]: value,
    }));
  };

  const handleSubmit = (event) => {
    event.preventDefault();
    console.log('Form submitted:', formData);
    // Here you can handle form submission (e.g., sending data to an API)
  };

  return (
    <form onSubmit={handleSubmit}>
      <div>
        <label>
          Name:
          <input
            type="text"
            name="name"
            value={formData.name}
            onChange={handleChange}
          />
        </label>
      </div>
      <div>
        <label>
          Email:
          <input
            type="email"
            name="email"
            value={formData.email}
            onChange={handleChange}
          />
        </label>
      </div>
      <button type="submit">Submit</button>
    </form>
  );
};

export default MyForm;

Explanation

1. State Management:

   • We use useState to create a formData state object that holds the values of the input fields.

2. Handle Change:

   • The handleChange function updates the state based on the user's input. It uses the name attribute of the input fields to update the correct property in the formData object.

3. Handle Submit:

   • The handleSubmit function prevents the default form submission behavior and can be used to process the form data (e.g., sending it to a server).

4. Controlled Inputs:

   • Each input field's value is controlled by React state, making it a controlled component. The value prop of the input is set to the corresponding state value, and the onChange event updates the state.

Advantages of Controlled Components

• Single Source of Truth: The form data is stored in a single state object, making it easy to manage.
• Validation and Formatting: You can easily implement validation and formatting directly in the handleChange function.
• Dynamic Inputs: Controlled components allow you to create dynamic forms based on state, such as adding or removing fields.

Tips

• Use onSubmit for form submission to handle user input efficiently.
• You can create reusable controlled components for input fields to reduce code duplication.
• Consider using libraries like Formik or React Hook Form for more complex forms, as they offer additional features like validation and easier state management.

Feel free to ask if you need more examples or specific implementations!

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