React三大组件--ref

1.定义：组件内的标签可以定义ref属性来标识自己。

2.使用ref的三种方法

• 字符串形式的ref （这个写法会慢慢替换掉，所以尽量不要写字符串形式）

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>1_字符串形式的ref</title>
</head>
<body>
    <div id="text"></div>

    <script src="../../js/react.development.js"></script> 
    <script src="../../js/react-dom.development.js"></script> 
    <script src="../../js/babel.min.js"></script> 
    <script type="text/babel">
        class Demo extends React.Component{
            // 左侧
            left = ()=>{
                const input = this.refs.input1
                alert(input.value)
                console.log(this.refs.input1)
            }
            // 右侧
            right = ()=>{
                const input = this.refs.input2
                alert(input.value)
            }
            render(){
                return (
                    <div>
                        <input ref="input1" type="text" placeholder="点击确定弹框" />
                        <button onClick={this.left}>确定</button>
                        <input ref="input2" onBlur={this.right} type="text" placeholder="失去焦点弹框" />
                    </div>

                )
            }
           
        }
        ReactDOM.render(<Demo />,document.getElementById('text'))
    </script>
</body>
</html>

• 回调形式的ref（主推用这个形式写）

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>2_回调形式的ref</title>
</head>
<body>
    <div id="text"></div>

    <script src="../../js/react.development.js"></script> 
    <script src="../../js/react-dom.development.js"></script> 
    <script src="../../js/babel.min.js"></script> 
    <script type="text/babel">
        class Demo extends React.Component{
            // 左侧
            left = ()=>{
                console.log('@',this)
                const input = this.input1
                alert(input.value)
                console.log(this)
            }
            // 右侧
            right = ()=>{
                const input = this.input2
                alert(input.value)
            }
            render(){
                return (
                    <div>
                        <input ref={(c)=>{this.input1 = c}} type="text" placeholder="点击确定弹框" />
                        <button onClick={this.left}>确定</button>
                        <input ref={(c)=>{this.input2 = c}} onBlur={this.right} type="text" placeholder="失去焦点弹框" />
                    </div>

                )
            }
           
        }
        ReactDOM.render(<Demo />,document.getElementById('text'))
    </script>
</body>
</html>

• createRef 创建 ref 容器（这个相对来说比较麻烦一些

  <div id="text"></div>
  <script src="../../js/react.development.js"></script> 
  <script src="../../js/react-dom.development.js"></script> 
  <script src="../../js/babel.min.js"></script> 
  <script type="text/babel">
      class Login extends React.Component {
          createRef1= React.createRef()
          createRef2= React.createRef()
          left= ()=>{
              const input = this.createRef1
              alter(input.value)
          }
          left= ()=>{
              const input = this.createRef2
              alter(input.value)
          }
          render(){
              //这样写是把username和password 放在了login中，如果还是很迷糊不知道在那的话，可以在left函数中输出this
              return (
                  <div>
                          <input ref={this.createRef1} type="text" placeholder="点击确定弹框" />
                          <button onClick={this.left}>确定</button>
                          <input ref={this.createRef2} onBlur={this.right} type="text" placeholder="失去焦点弹框" />
                      </div>
              )
          }
      }
      ReactDOM.render(<Login />,document.getElementById('text'))
  </script>