Question

内容很少，我正在尝试创建一个表单来获取用户注册。

我首先编写如下代码。

import { useState } from 'react';


const SignupComponent = () => {
const [formData, setFormData] = useState({
    name: '',
    email: '',
    password: '',
    error: '',
    loading: false,
    message: '',
    showForm: true
})

const { name, email, password, error, loading, showForm } = formData;

const onChange = e => {
    setFormData({ ...formData, error: false, [e.target.name]: e.target.value })
    console.log(name)

}
const handleSubmit = async e => {
    e.preventDefault();
    console.table({ name, email, password, error, loading, showForm })
}


const signupForm = () => {
    return (
        <form onSubmit={handleSubmit}>
            <div className="form-group">
                <input type="text" className="form-control" placeholder="Enter Your Name" values={name} onChange={e => onChange(e)} />
            </div>

            <div className="form-group">
                <input values={email} onChange={e => onChange(e)} type="email" className="form-control" placeholder="Enter Your Email" />
            </div>

            <div className="form-group">
                <input values={password} onChange={e => onChange(e)} type="password" className="form-control" placeholder="Enter Your Password" />
            </div>

            <div>
                <button className="btn btn-primary">Signup</button>
            </div>
        </form>
    );

};
return <React.Fragment>{signupForm()}</React.Fragment>};
export default SignupComponent;

我注意到在此代码段中，setFormData中的状态没有得到更新，控制台日志记录名称或任何其他值返回一个空字符串。

result for the above code

但是在调整了代码之后

import { useState } from 'react';


const SignupComponent = () => {
const [formData, setFormData] = useState({
    name: '',
    email: '',
    password: '',
    error: '',
    loading: false,
    message: '',
    showForm: true
})

const { name, email, password, error, loading, showForm } = formData;

const handleChange = value => (e) => {
    setFormData({ ...formData, error: false, [value]: e.target.value })
    console.log(name)

}
const handleSubmit = async e => {
    e.preventDefault();
    console.table({ name, email, password, error, loading, showForm })
}


const signupForm = () => {
    return (
        <form onSubmit={handleSubmit}>
            <div className="form-group">
                <input type="text" className="form-control" placeholder="Enter Your Name" values={name} onChange={handleChange('name')} />
            </div>

            <div className="form-group">
                <input values={email} onChange={handleChange('email')} type="email" className="form-control" placeholder="Enter Your Email" />
            </div>

            <div className="form-group">
                <input values={password} onChange={handleChange('password')} type="password" className="form-control" placeholder="Enter Your Password" />
            </div>

            <div>
                <button className="btn btn-primary">Signup</button>
            </div>
        </form>
    );

};
return <React.Fragment>{signupForm()}</React.Fragment> };
export default SignupComponent;

使代码正常工作，结果是所希望的。就像这张图片一样。 2nd way

这是为什么这样的。为什么第一种方法不起作用。

Answer 1

您忘记了输入中的name属性，而没有s的value属性

<input name="email" value={email} onChange={onChange} ... />

然后

const onChange = e => {
    // The event will get passed as an argument even if you don't bind it in onChange={onChange}.
    console.log(e.target.name, e.target.value)
    setFormData({ ...formData, error: false, [e.target.name]: e.target.value })
}

该事件将作为参数传递。

它适用于您将名称作为参数传递的第二个原因

Answer 2

请参阅文档，https://reactjs.org/docs/thinking-in-react.html

React的单向数据流（也称为单向绑定）使一切保持模块化和快速。

重要的事情来解决你的问题。

已更改功能组件（FC）状态，重新呈现UI。
但是，您的signupForm渲染函数是在FC中声明的。
因此，当SignupComponent状态更改时，它将作为新项重新运行。

首先。将signupForm渲染功能更改为FC组件。

第二，将道具传递到组件。蒂里德，重新使用它们。

import React from 'react'; // React is required to render JSX

const FormInput = ({
  type,
  placeholder,
  value,
  onChange,
}) => (
  <div className="form-group">
    <input type={type} className="form-control" placeholder={placeholder} value={value} onChange={onChange} />
  </div>
);

const SignupComponent = () => {
  const [formData, setFormData] = React.useState({
    name: '',
    email: '',
    password: '',
    error: false,
    loading: false,
    message: '',
    showForm: true,
  });

  const {
    name, email, password, error, loading, showForm,
  } = formData;

  const handleChange = (value) => (e) => {
    setFormData({
      ...formData,
      error: false,
      [value]: e.target.value,
    });
    console.log(name);
  };

  const handleSubmit = async (e) => {
    e.preventDefault();
    console.table({
      name, email, password, error, loading, showForm,
    });
  };

  return (
    <form onSubmit={handleSubmit}>
      <FormInput type="text" value={name} placeholder="Enter Your Name" onChange={handleChange('name')} />
      <div>
        <button type="submit" className="btn btn-primary">Signup</button>
      </div>
    </form>
  );
};

export default SignupComponent;

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>

useState（）挂钩在更改时不更新值

2 个答案: