React ref 当前为 NULL

Question

我从官方 React Ref 文档中获取了这段代码

import React from "react";
import { render } from "react-dom";

class CustomTextInput extends React.Component {
  constructor(props) {
    super(props);
    // create a ref to store the textInput DOM element
    this.textInput = React.createRef();
    this.focusTextInput = this.focusTextInput.bind(this);
  }

  focusTextInput() {
    // Explicitly focus the text input using the raw DOM API
    // Note: we're accessing "current" to get the DOM node
    // this.textInput.current.focus();
    console.log(this.textInput);
  }

  render() {
    // tell React that we want to associate the <input> ref
    // with the `textInput` that we created in the constructor
    return (
      <div>
        <input
          type="text"
          ref={this.textInput} />

        <input
          type="button"
          value="Focus the text input"
          onClick={this.focusTextInput}
        />
      </div>
    );
  }
}
const A = () => {
  return <div>
    <CustomTextInput />
  </div>
}
render(<div><A/></div>, document.getElementById("root"));

当调用 focusTextInput 时，它会记录 "current: null"。这是演示：https://codesandbox.io/s/wo6qjk9xk7

Answer 1

代码很好，因为它是文档中的 exact same example present in react docs. Problem is your react-dom version is older. React.createRef() API was introduced in React 16.3 (all react related packages should be 16.3+ in order to use React.createRef()). Check this reference。

您的依赖项：

 "dependencies": {
    "react": "16.6.3",
    "react-dom": "16.2.0"
  },

将 react-dom 更新到 16.6.3

后问题已解决

检查这个：https://codesandbox.io/s/n7ozx9kr0p

React ref 当前为 NULL

React ref current is NULL

ref

reactjs