× 错误：元素类型无效：应为字符串或类/函数，但得到：对象。检查`App`的render方法

Question

我试图使用 react app 制作表单，为此我制作了以下组件，但是当我在本地服务器上运行它时，它显示

错误：元素类型无效：应为字符串（对于内置组件）或类/函数（对于复合组件）但得到：对象。您可能忘记从定义组件的文件中导出组件，或者您可能混淆了默认导入和命名导入。

检查 App 的渲染方法。 Error while I run on localhost

请帮我解决这个问题。

我附上了组件文件 FormSuccess.js、useForm.js、validateInfo.js、App.js、App.css、FormSignup.js、Form.js、index.js、Form.css

import React from 'react';
import './Form.css';

const FormSuccess = () => {
  return (
    <div className='form-content-right'>
      <h1 className='form-success'>We have received your request!</h1>
      <img className='form-img-2' src='img/img-3.svg' alt='success-image' />
    </div>
  );
};

export default FormSuccess;

import useState from 'react';
import useEffect from 'react';

const useForm = (callback, validate) => {
  const [values, setValues] = useState({
    username: '',
    email: '',
    password: '',
    password2: ''
  });
  const [errors, setErrors] = useState({});
  const [isSubmitting, setIsSubmitting] = useState(false);

  const handleChange = e => {
    const { name, value } = e.target;
    setValues({
      ...values,
      [name]: value
    });
  };

  const handleSubmit = e => {
    e.preventDefault();

    setErrors(validate(values));
    setIsSubmitting(true);
  };

  useEffect(
    () => {
      if (Object.keys(errors).length === 0 && isSubmitting) {
        callback();
      }
    },
    [errors]
  );

  return { handleChange, handleSubmit, values, errors };
};

export default useForm;

export default function validateInfo(values) {
    let errors = {};
  
    if (!values.username.trim()) {
      errors.username = 'Username required';
    }
    // else if (!/^[A-Za-z]+/.test(values.name.trim())) {
    //   errors.name = 'Enter a valid name';
    // }
  
    if (!values.email) {
      errors.email = 'Email required';
    } else if (!/\S+@\S+\.\S+/.test(values.email)) {
      errors.email = 'Email address is invalid';
    }
    if (!values.password) {
      errors.password = 'Password is required';
    } else if (values.password.length < 6) {
      errors.password = 'Password needs to be 6 characters or more';
    }
  
    if (!values.password2) {
      errors.password2 = 'Password is required';
    } else if (values.password2 !== values.password) {
      errors.password2 = 'Passwords do not match';
    }
    return errors;
  }

import React from 'react';
import './App.css';
import Form from './Form';

function App() {
  return <Form />;
}

export default App;

@import url('https://fonts.googleapis.com/css2?family=PT+Sans&display=swap');

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  font-family: 'PT Sans', sans-serif;
}

import React from 'react';
import validate from './validateInfo';
import useForm from './useForm';
import './Form.css';

const FormSignup = ({ submitForm }) => {
  const { handleChange, handleSubmit, values, errors } = useForm(
    submitForm,
    validate
  );

  return (
    <div className='form-content-right'>
      <form onSubmit={handleSubmit} className='form' noValidate>
        <h1>
          Get started with us today! Create your account by filling out the
          information below.
        </h1>
        <div className='form-inputs'>
          <label className='form-label'>Username</label>
          <input
            className='form-input'
            type='text'
            name='username'
            placeholder='Enter your username'
            value={values.username}
            onChange={handleChange}
          />
          {errors.username && <p>{errors.username}</p>}
        </div>
        <div className='form-inputs'>
          <label className='form-label'>Email</label>
          <input
            className='form-input'
            type='email'
            name='email'
            placeholder='Enter your email'
            value={values.email}
            onChange={handleChange}
          />
          {errors.email && <p>{errors.email}</p>}
        </div>
        <div className='form-inputs'>
          <label className='form-label'>Password</label>
          <input
            className='form-input'
            type='password'
            name='password'
            placeholder='Enter your password'
            value={values.password}
            onChange={handleChange}
          />
          {errors.password && <p>{errors.password}</p>}
        </div>
        <div className='form-inputs'>
          <label className='form-label'>Confirm Password</label>
          <input
            className='form-input'
            type='password'
            name='password2'
            placeholder='Confirm your password'
            value={values.password2}
            onChange={handleChange}
          />
          {errors.password2 && <p>{errors.password2}</p>}
        </div>
        <button className='form-input-btn' type='submit'>
          Sign up
        </button>
        <span className='form-input-login'>
          Already have an account? Login <a href='#'>here</a>
        </span>
      </form>
    </div>
  );
};

export default FormSignup;

import React from 'react';
import useState from 'react';
import './Form.css';
import FormSignup from './FormSignup';
import FormSuccess from './FormSuccess';

const Form = () => {
  const [isSubmitted, setIsSubmitted] = useState(false);

  function submitForm() {
    setIsSubmitted(true);
  }
  return (
    <>
      <div className='form-container'>
        <span className='close-btn'>×</span>
        <div className='form-content-left'>
          <img className='form-img' src='img/img-2.svg' alt='spaceship' />
        </div>
        {!isSubmitted ? (
          <FormSignup submitForm={submitForm} />
        ) : (
          <FormSuccess />
        )}
      </div>
    </>
  );
};

export default Form;

import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';

ReactDOM.render(
  <React.StrictMode>
    <App />
  </React.StrictMode>,
  document.getElementById('root')
);

.form-container {
    margin: 100px auto;
    width: 1000px;
    box-shadow: 0 5px 8px 0 rgba(0, 0, 0, 0.2), 0 7px 20px 0 rgba(0, 0, 0, 0.2);
    position: relative;
    border-radius: 10px;
    height: 600px;
    display: grid;
    grid-template-columns: 1fr 1fr;
  }
  
  .close-btn {
    position: absolute;
    top: 2%;
    right: 3%;
    font-size: 1.5rem;
    z-index: 1;
    color: #fff;
    cursor: pointer;
  }
  
  .form-content-left {
    background: linear-gradient(
      90deg,
      rgb(39, 176, 255) 0%,
      rgb(0, 232, 236) 100%
    );
    border-radius: 10px 0 0 10px;
    position: relative;
  }
  
  .form-img {
    width: 80%;
    height: 80%;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
  }
  
  .form-img-2 {
    width: 60%;
    height: 60%;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
  }
  
  .form-success {
    text-align: center;
    font-size: 24px;
    margin-top: 80px;
    color: #fff;
  }
  
  .form-content-right {
    border-radius: 0 10px 10px 0;
    position: relative;
    background: linear-gradient(90deg, rgb(40, 40, 40) 0%, rgb(17, 17, 17) 100%);
  }
  
  .form {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 90%;
    height: 100%;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
  }
  
  .form h1 {
    font-size: 1rem;
    text-align: start;
    width: 80%;
    margin-bottom: 1rem;
    color: #fff;
  }
  
  .form-inputs {
    margin-bottom: 0.5rem;
    width: 80%;
  }
  
  .form-inputs p {
    font-size: 0.8rem;
    margin-top: 0.5rem;
    color: #f00e0e;
  }
  
  .form-label {
    display: inline-block;
    font-size: 0.8rem;
    margin-bottom: 6px;
    color: #fff;
  }
  
  .form-input {
    display: block;
    padding-left: 10px;
    outline: none;
    border-radius: 2px;
    height: 40px;
    width: 100%;
    border: none;
  }
  
  .form-input::placeholder {
    color: #595959;
    font-size: 12px;
  }
  
  .form-input-btn {
    width: 80%;
    height: 50px;
    margin-top: 10px;
    border-radius: 2px;
    background: linear-gradient(
      90deg,
      rgb(39, 176, 255) 0%,
      rgb(0, 232, 236) 100%
    );
    outline: none;
    border: none;
    color: #fff;
    font-size: 1rem;
  }
  
  .form-input-btn:hover {
    cursor: pointer;
    background: linear-gradient(
      90deg,
      rgb(39, 143, 255) 0%,
      rgb(12, 99, 250) 100%
    );
    transition: all 0.4s ease-out;
  }
  
  .form-input-login {
    font-size: 0.8rem;
    margin-top: 10px;
    color: #fff;
    width: 80%;
    text-align: center;
  }
  
  .form-input-login a {
    text-decoration: none;
    color: #27cdff;
    font-weight: 600;
  }