[移动开发] react16：使用ref

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[移动开发]react16：使用ref

文章目录

ref是一个字符串

react官网不推荐使用字符串形式的ref，它可能在未来的某个版本被移除。
<input type="text" ref="input1"/>，
<input type="text" ref="input2"/>，
组件实例的refs属性上以key-value的形式保存着真实DOM元素。
在这里插入图片描述

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>test</title>
    <script src="./js/react.development.js"></script>
    <script src="./js/react-dom.development.js"></script>
    <script src="./js/babel.min.js"></script>
</head>

<body>
    <div id="app"></div>
    <script type="text/babel">
        class Login extends React.Component {

            showData = () => {
                console.log(this);
                alert(this.refs.input1.value);
            }
            showData2 = () => {
                alert(this.refs.input2.value);
            }
            render() {
                return (
                    <div>
                        <div>
                            <input type="text" placeholder="点击按钮提示数据"  ref="input1"/>&nbsp;
                            <button onClick={this.showData}>点我提示数据</button>
                        </div>
                        <input type="text" placeholder="失去焦点提示数据" onBlur={this.showData2} ref="input2" />
                    </div>
                )
            }
        }

        ReactDOM.render(<Login />, document.getElementById("app"));
    </script>
</body>

</html>

在这里插入图片描述

ref是一个回调函数

回调函数是内联形式

<input type="text" ref={c => this.input1 = c}/>，
<input type="text" ref={c => this.input2 = c} />
回调函数的参数，就是真实的DOM元素。
在这里插入图片描述

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>test</title>
    <script src="./js/react.development.js"></script>
    <script src="./js/react-dom.development.js"></script>
    <script src="./js/babel.min.js"></script>
</head>

<body>
    <div id="app"></div>
    <script type="text/babel">
        class Login extends React.Component {

            showData = () => {
                console.log(this.input1);
                alert(this.input1.value);
            }
            showData2 = () => {
                console.log(this.input2);
                alert(this.input2.value);
            }
            render() {
                return (
                    <div>
                        <div>
                            <input type="text" placeholder="点击按钮提示数据"  ref={c => this.input1 = c}/>&nbsp;
                            <button onClick={this.showData}>点我提示数据</button>
                        </div>
                        <input type="text" placeholder="失去焦点提示数据" onBlur={this.showData2} ref={c => this.input2 = c} />
                    </div>
                )
            }
        }

        ReactDOM.render(<Login />, document.getElementById("app"));
    </script>
</body>

</html>

在这里插入图片描述
回调函数是内联函数时，组件更新过程会执行两次回调。回调第一次执行，返回null；回调第二次执行，返回真实DOM元素。这是因为每次渲染时都会创建新的函数实例，react会清除旧的ref并设置新的。如下。

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>test</title>
    <script src="./js/react.development.js"></script>
    <script src="./js/react-dom.development.js"></script>
    <script src="./js/babel.min.js"></script>
</head>

<body>
    <div id="app"></div>
    <script type="text/babel">
        class Login extends React.Component {
            state = {
                isHot:false
            }
            changeWeather = () => {
                const {isHot} = this.state;
                this.setState({
                    isHot:!isHot
                })
            }
            showData = () => {
                console.log(this.input1);
                alert(this.input1.value);
            }
            showData2 = () => {
                console.log(this.input2);
                alert(this.input2.value);
            }
            render() {
                const {isHot} = this.state;
                const {changeWeather,showData,showData2} = this;
                return (
                    <div>
                        <h2 onClick={changeWeather}>今天天气很{isHot ? "炎热" : "凉爽"}</h2>
                        <div>
                            <input type="text" placeholder="点击按钮提示数据"  ref={c => {this.input1 = c;console.log("@",c)}}/>&nbsp;
                            <button onClick={showData}>点我提示数据</button>
                        </div>
                        <input type="text" placeholder="失去焦点提示数据" onBlur={showData2} ref={c => this.input2 = c} />
                    </div>
                )
            }
        }

        ReactDOM.render(<Login />, document.getElementById("app"));
    </script>
</body>

</html>

在这里插入图片描述
react官网说，虽然更新过程中，内联形式的回调函数会执行两次，但大多数情况下无关紧要。

回调函数绑定在类实例上

<input type="text" ref={saveInput1}/>，
<input type="text" ref={saveInput2} />，

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>test</title>
    <script src="./js/react.development.js"></script>
    <script src="./js/react-dom.development.js"></script>
    <script src="./js/babel.min.js"></script>
</head>

<body>
    <div id="app"></div>
    <script type="text/babel">
        class Login extends React.Component {
            state = {
                isHot:false
            }
            changeWeather = () => {
                const {isHot} = this.state;
                this.setState({
                    isHot:!isHot
                })
            }
            saveInput1 = (c) => {
                this.input1 = c;
                console.log("@",c);
            }
            saveInput2 = (c) => {
                this.input2 = c;
            }
            showData = () => {
                console.log(this.input1);
                alert(this.input1.value);
            }
            showData2 = () => {
                console.log(this.input2);
                alert(this.input2.value);
            }
            render() {
                const {isHot} = this.state;
                const {changeWeather,showData,showData2,saveInput1,saveInput2} = this;
                return (
                    <div>
                        <h2 onClick={changeWeather}>今天天气很{isHot ? "炎热" : "凉爽"}</h2>
                        <div>
                            <input type="text" placeholder="点击按钮提示数据"  ref={saveInput1}/>&nbsp;
                            <button onClick={showData}>点我提示数据</button>
                        </div>
                        <input type="text" placeholder="失去焦点提示数据" onBlur={showData2} ref={saveInput2} />
                    </div>
                )
            }
        }

        ReactDOM.render(<Login />, document.getElementById("app"));
    </script>
</body>

</html>

在这里插入图片描述

createRef

myRef = React.createRef()，createRef()将返回一个容器，用于保存ref标识的节点。
<input type="text" ref={myRef}/>，ref属性标识目标元素。
this.myRef.current，访问目标元素。

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>test</title>
    <script src="./js/react.development.js"></script>
    <script src="./js/react-dom.development.js"></script>
    <script src="./js/babel.min.js"></script>
</head>

<body>
    <div id="app"></div>
    <script type="text/babel">
        class Login extends React.Component {

            myRef = React.createRef();
            myRef2 = React.createRef();
            showData = () => {
                console.log(this.myRef);
                alert(this.myRef.current.value);
            }
            showData2 = () => {
                console.log(this.myRef2);
                alert(this.myRef2.current.value);
            }
            render() {
                const {showData,showData2,myRef,myRef2} = this;
                return (
                    <div>
                        <div>
                            <input type="text" placeholder="点击按钮提示数据"  ref={myRef}/>&nbsp;
                            <button onClick={showData}>点我提示数据</button>
                        </div>
                        <input type="text" placeholder="失去焦点提示数据" onBlur={showData2} ref={myRef2} />
                    </div>
                )
            }
        }

        ReactDOM.render(<Login />, document.getElementById("app"));
    </script>
</body>

</html>

在这里插入图片描述

不要过度使用ref

不要过度使用ref。比如，上述例子里，第二个input就没必要用ref，在事件回调中使用event.target即可获取输入框的文本值。

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>test</title>
    <script src="./js/react.development.js"></script>
    <script src="./js/react-dom.development.js"></script>
    <script src="./js/babel.min.js"></script>
</head>

<body>
    <div id="app"></div>
    <script type="text/babel">
        class Login extends React.Component {

            myRef = React.createRef();
            showData = () => {
                alert(this.myRef.current.value);
            }
            showData2 = (event) => {
                alert(event.target.value);
            }
            render() {
                const {showData,showData2,myRef,myRef2} = this;
                return (
                    <div>
                        <div>
                            <input type="text" placeholder="点击按钮提示数据"  ref={myRef}/>&nbsp;
                            <button onClick={showData}>点我提示数据</button>
                        </div>
                        <input type="text" placeholder="失去焦点提示数据" onBlur={showData2}/>
                    </div>
                )
            }
        }

        ReactDOM.render(<Login />, document.getElementById("app"));
    </script>
</body>

</html>