class CustomTextInput extends React.Component {
 constructor(props) {
 super(props);

 this.textInput = null;

 this.setTextInputRef = element => {
  this.textInput = element;
 };

 this.focusTextInput = () => {
  // Focus the text input using the raw DOM API
  if (this.textInput) this.textInput.focus();
 };
 }

 componentDidMount() {
 // autofocus the input on mount
 this.focusTextInput();
 }

 render() {
 // Use the `ref` callback to store a reference to the text input DOM
 // element in an instance field (for example, this.textInput).
 return (
  <div>
  <input
   type="text"
   ref={this.setTextInputRef}
  />
  <input
   type="button"
   value="Focus the text input"
   onClick={this.focusTextInput}
  />
  </div>
 );
 }
}

class Example extends React.Component {
 handleClick() {
 // 使用原生的 DOM API 获取焦点
 this.refs.myInput.focus
 ();
 }
 render() {
 // 当组件插入到 DOM 后，ref 属性添加一个组件的引用于到 this.refs
 return (
  <div>
  <input type="text" ref="myInput" />
  <input
   type="button"
   value="点我输入框获取焦点"
   onClick={this.handleClick.bind(this)}
  />
  </div>
 );
 }
}

class MyComponent extends React.Component {
 constructor(props) {
 super(props);
 this.myRef = React.createRef();
 }
 render() {
 return <div ref={this.myRef} />;
 }
}

const node = this.myRef.current;

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();
 }

 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>
 );
 }
}

function MyFunctionComponent() {
 return <input />;
}

class Parent extends React.Component {
 constructor(props) {
 super(props);
 this.textInput = React.createRef();
 }
 render() {
 // This will *not* work!
 return (
  <MyFunctionComponent ref={this.textInput} />
 );
 }
}

function CustomTextInput(props) {
 // textInput must be declared here so the ref can refer to it
 let textInput = React.createRef();

 function handleClick() {
 textInput.current.focus();
 }

 return (
 <div>
  <input
  type="text"
  ref={textInput} />

  <input
  type="button"
  value="Focus the text input"
  onClick={handleClick}
  />
 </div>
 );
}