React "this“在函数中始终为空

class MyComponent extends React.Component {
  handleClick = () => {
    // 使用箭头函数定义方法
    console.log(this.props);
  }

  render() {
    return (
      <button onClick={this.handleClick}>Click me</button>
    );
  }
}

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.handleClick = this.handleClick.bind(this);
  }

  handleClick() {
    // 使用bind()方法绑定this
    console.log(this.props);
  }

  render() {
    return (
      <button onClick={this.handleClick}>Click me</button>
    );
  }
}

class MyComponent extends React.Component {
  handleClick = () => {
    // 使用公共类字段语法定义方法
    console.log(this.props);
  }

  render() {
    return (
      <button onClick={this.handleClick}>Click me</button>
    );
  }
}