反应参考电流为 NULL

Question

我的代码取自官方 React Ref 文档

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，因为它与react 文档中的示例完全相同。问题是您的react-dom版本较旧。React.createRef()API 是在 React 16.3 中引入的（所有react相关的包都应该是 16.3+ 才能使用React.createRef()）。检查文档中的此参考。

您的依赖项：

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

更新react-dom到 16.6.3后问题已修复

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