React-其它内容-Fragment

由于 React 规定, 组件中只能有一个根元素
所以每次编写组件的时候, 我们都需要在最外层包裹一个冗余的标签

import React from 'react';

class Home extends React.PureComponent {
    constructor(props) {
        super(props);
        this.state = {
            heroList: ['鲁班', '虞姬', '黄忠']
        }
    }

    render() {
        return (
            <div>
                <p>{this.state.heroList[0]}</p>
                <p>{this.state.heroList[1]}</p>
                <p>{this.state.heroList[2]}</p>
            </div>
        )
    }
}

class App extends React.PureComponent {
    render() {
        return (
            <Home/>
        )
    }
}

export default App;

如果不想渲染这个冗余的标签, 那么就可以使用 Fragment 来代替

import React from 'react';

class Home extends React.PureComponent {
    constructor(props) {
        super(props);
        this.state = {
            heroList: ['鲁班', '虞姬', '黄忠']
        }
    }

    render() {
        return (
            <React.Fragment>
                <p>{this.state.heroList[0]}</p>
                <p>{this.state.heroList[1]}</p>
                <p>{this.state.heroList[2]}</p>
            </React.Fragment>
        )
    }
}

class App extends React.PureComponent {
    render() {
        return (
            <Home/>
        )
    }
}

export default App;

语法糖

React.Fragment 的简化写法

import React from 'react';

class Home extends React.PureComponent {
    constructor(props) {
        super(props);
        this.state = {
            heroList: ['鲁班', '虞姬', '黄忠']
        }
    }

    render() {
        return (
            <>
                <p>{this.state.heroList[0]}</p>
                <p>{this.state.heroList[1]}</p>
                <p>{this.state.heroList[2]}</p>
            </>
        )
    }
}

class App extends React.PureComponent {
    render() {
        return (
            <Home/>
        )
    }
}

export default App;

如果需要给 Fragment 添加 key, 那么就不能使用语法糖写法

import React from 'react';

class Home extends React.PureComponent {
    constructor(props) {
        super(props);
        this.state = {
            heroList: ['鲁班', '虞姬', '黄忠']
        }
    }

    render() {
        return (
            <>
                {
                    this.state.heroList.map(name => {
                        return (
                            <React.Fragment key={name}>
                                <p>{name}</p>
                            </React.Fragment>
                        )
                    })
                }
            </>
        );
    }
}

class App extends React.PureComponent {
    render() {
        return (
            <Home/>
        )
    }
}

export default App;