React基础语法学习

╰半夏微凉° 2022-09-21 14:26 177阅读 0赞

**React主要有如下3个特点：**

*  作为UI（Just the UI）
 *  虚拟DOM（Virtual DOM）:这是亮点 是React最重要的一个特性 放进内存 最小更新的视图,差异部分更新 diff算法
 *  数据流（Date Flow）单向数据流

**学习React需要掌握哪些知识？**

*  JSX语法 类似XML
 *  ES6相关知识
 *  前端基础 CSS+DIV JS

**例子一**  
（简单组件和数据传递） 使用this.props 指向自己的属性

<!DOCTYPE html>
    <html>
    <head lang="en">
        <meta charset="UTF-8">
        <title>React第一个例子</title>
        <script type="text/javascript" src="react.js"></script>
        <script type="text/javascript" src="react-dom.js"></script>
        <script type="text/javascript" src="browser.min.js"></script>
    </head>
    <body>
    <div id="example"></div>
    <script type="text/babel">
        var HelloMessage=React.createClass(
                {
                    render:function(){
          
                        return <h1 style={
        {
        color:'#ff0000',fontSize:'24px'}} >Hello {
         this.props.name}!我是东方耀</h1>;
                        //这是注释  React.createElement
                    }
                }
        );
    
        ReactDOM.render(<HelloMessage name="React 语法基础8" /> ,document.getElementById('example'));
    
    
    
    
    </script>
    </body>
    </html>

**例子二（通过this.state更新视图）**

<!DOCTYPE html>
    <html>
    <head lang="en">
        <meta charset="UTF-8">
        <title>React第二个例子</title>
        <script type="text/javascript" src="react.js"></script>
        <script type="text/javascript" src="react-dom.js"></script>
        <script type="text/javascript" src="browser.min.js"></script>
    </head>
    <body>
    
    <div id="example"></div>
    
    <script type="text/babel">
        var Timer=React.createClass(
                {
          /*初始状态*/
                getInitialState:function(){
         
          return {secondsElapsed:0};
        },
    
        tick:function(){
         
          this.setState({secondsElapsed:this.state.secondsElapsed+1});
        },
    
        /*组件完成装载*/
        componentDidMount:function(){
         
          this.interval=setInterval(this.tick,1000);
        },
        /*组件将被卸载   清除定时器*/
        componentWillUnmount:function(){
         
            clearInterval(this.interval);
        },
        /*渲染视图*/
        render:function(){
         
            return(
                    <div> Seconds Elapsed:{this.state.secondsElapsed} </div>
            );
        }
    
        }
        );
    
    
    
    
        React.render( <Timer /> ,document.getElementById('example'));
    
    
    </script>
    
    </body>
    </html>

**例子三（简单应用）**

<!DOCTYPE html>
    <html>
    <head lang="en">
        <meta charset="UTF-8">
        <title>React第三个例子</title>
        <script type="text/javascript" src="react.js"></script>
        <script type="text/javascript" src="react-dom.js"></script>
        <script type="text/javascript" src="browser.min.js"></script>
    </head>
    <body>
    
    <div id="example"></div>
    
    <script type="text/babel">
    
        var ShowEditor=React.createClass(
                {
                    getInitialState:function(){
          
                      return {value:'你可以在这里输入文字'};
                    },
    
                    handleChange:function(){
          
                      this.setState({value:React.findDOMNode(this.refs.textarea).value});
                    },
    
                    render:function(){
          
                        return (
    
    
    
                                <div>
                                <h3>输入</h3>
                                        <textarea style={
        {
        width:300,height:150,outline:'none'}}
                           onChange={
         this.handleChange}
                           ref="textarea"
                        defaultValue={
         this.state.value}
    
                    />
        <h3>输出</h3>
    
                <div> {this.state.value} </div>
    
                                </div>
    
                        );
    
                    }
    
    
    
    
                }
    
        );
    
    
        React.render(<ShowEditor />,document.getElementById('example'));
    
    
    
    </script>
    
    </body>
    </html>

### flexbox布局 ###

**伸缩项目的属性**

1.order  
定义项目的排列顺序，数值越小，排列越靠前，默认值为0，语法为：order：整数值  
2.flex-grow  
定义伸缩项目的放大比例，默认值为0，即表示如果存在剩余空间，也不放大，语法为：flex-grow：整  
数值  
3.flex-shrink  
定义伸缩项目的收缩能力，默认值为1 ，其语法为：flex-shrink:整数值  
4.flex-basis  
用来设置伸缩项目的基准值，剩余的空间按比率进行伸缩，其语法为：flex-basis:length | auto，默认  
值为auto  
5.flex  
是flex-grow flex-shrink flex-basis这三个属性的缩写，其语法为：flex:none | flex-grow flex-shrink flexbasis，  
其中第二个和第三个参数为可选参数，默认值为：0 1 auto  
6.align-self  
用来设置单独的伸缩项目在交叉轴上的对齐方式，会覆盖默认的对齐方式，其语法为：align-self:auto  
| flex-start | flex-end | center | baseline | stretch(伸缩项目在交叉轴方向占满伸缩容器，如果交叉轴为  
垂直方向的话，只有在不设置高度的情况下才能看到效果)

**在React Native中使用flexbox**

RN目前主要支持flexbox的如下6个属性：  
1.alignItems  
用来定义伸缩项目在交叉轴上的对齐方式，语法为： alignItems:flex-start（默认值） | flex-end |  
center | stretch  
2.alignSelf  
用来设置单独的伸缩项目在交叉轴上的对齐方式，会覆盖默认的对齐方式，其语法为：alignSelf:auto |  
flex-start | flex-end | center | stretch(伸缩项目在交叉轴方向占满伸缩容器，如果交叉轴为垂直方向的  
话，只有在不设置高度的情况下才能看到效果)  
3.flex  
是flex-grow flex-shrink flex-basis这三个属性的缩写，其语法为：flex:none | flex-grow flex-shrink flexbasis，  
其中第二个和第三个参数为可选参数，默认值为：0 1 auto  
4.flexDirection  
指定主轴的方向 flex-direction:row| row-reverse | column（默认值） | column-reverse  
5.flexWrap  
6.justifyContent

**BOX实现**

<!DOCTYPE html>
    <html>
      <head>
        <meta charset="utf-8">
        <title></title>
        <style>
          .height50 {
            height: 50px;
          }
          .height400 {
            height: 400px;
          }
          .height300 {
            height: 300px;
          }
          .height200 {
            height: 200px;
          }
          .height100 {
            height: 100px;
          }
          .width400 {
            width: 400px;
          }
          .bgred {
            background-color: #6AC5AC;
          }
          .bggreen {
            background-color:  #414142;
          }
          .bgyellow {
            background-color: #D64078;
          }
          .box {
            display: flex;
            flex-direction: column;
            flex: 1;
            position: relative;
            color: #FDC72F;
            line-height: 1em;
          }
          .label {
            top: 0;
            left: 0;
            padding: 0 3px 3px 0;
            position: absolute;
            background-color: #FDC72F;
            color: white;
            line-height: 1em;
          }
          .top {
            width: 100%;
            justify-content: center;
            display: flex;
            align-items: center;
          }
          .bottom {
            width: 100%;
            display: flex;
            justify-content: center;
            align-items: center;
          }
          .right {
            width: 50px;
            display: flex;
            justify-content: space-around;
            align-items: center;
          }
          .left {
            width: 50px;
            display: flex;
            justify-content: space-around;
            align-items: center;
          }
          .heightdashed {
            position: absolute;
            right: 20px;
            height: 100%;
            border-left: 1px solid #FDC72F;
          }
          .widthdashed {
            position: absolute;
            left: 0px;
            width: 100%;
            bottom: 24px;
            border-top: 1px solid #FDC72F;
          }
          .margginBox {
            position:absolute;
            top: 100px;
            padding-left:7px;
            padding-right:7px;
          }
          .borderBox {
            flex: 1;
            display: flex;
            justify-content: space-between;
          }
          .paddingBox {
            flex: 1;
            display: flex;
            justify-content: space-between;
          }
          .elementBox{
            flex: 1;
            display: flex;
            justify-content: space-between;
          }
          .measureBox {
            flex: 1;
            display: flex;
            justify-content: flex-end;
            align-items: flex-end;
          }
        </style>
      </head>
      <body>
        <span class="margginBox">
          <span class="box height400  width400">
            <span class="label">
              margin
            </span>
            <span class="top height50 bgred">
              top
            </span>
            <span class="borderBox">
              <span class="left bgred">
                left
              </span>
              <span class="box height300  ">
                <span class="label">
                  border
                </span>
                <span class="top height50 bggreen">
                  top
                </span>
                <span class="paddingBox">
                  <span class="left bggreen">
                    left
                  </span>
                  <span class="box height200  ">
                    <span class="label">
                      padding
                    </span>
                    <span class="top height50 bgyellow">
                      top
                    </span>
                    <span class="elementBox">
                      <span class="left bgyellow">
                        left
                      </span>
                      <span class="box height100  ">
                        <span class="label">
                          element
                        </span>
                        <span class="widthdashed">
                        </span>
                        <span class="heightdashed">
                        </span>
                        <span class="measureBox">
                          <span class="right">
                            height
                          </span>
                        </span>
                        <span class="bottom  height50">
                          width
                        </span>
                      </span>
                      <span class="right bgyellow">
                        right
                      </span>
                    </span>
                    <span class="bottom  height50 bgyellow">
                      bottom
                    </span>
                  </span>
                  <span class="right bggreen">
                    right
                  </span>
                </span>
                <span class="bottom  height50 bggreen">
                  bottom
                </span>
              </span>
              <span class="right bgred">
                right
              </span>
            </span>
            <span class="bottom  height50 bgred">
              bottom
            </span>
          </span>
        </span>
      </body>
    </html>

**效果如下**

![这里写图片描述][20160623132351915]

**ReactNative版实现**

/**
     * Sample React Native App
     * https://github.com/facebook/react-native
     */
    'use strict';
    import React, {
      AppRegistry,
      Component,
      StyleSheet,
      Text,
      View
    } from 'react-native';
    
    class DongFang extends Component {
      render() {
        return (
            <View style={[BoxStyles.margginBox]}  ref="lab1">
              <View style={[BoxStyles.box,BoxStyles.height400,BoxStyles.width400]}>
                <View style={[BoxStyles.top,BoxStyles.height50,BoxStyles.bgred]}>
                  <Text style={BoxStyles.yellow}>top</Text></View>
                <View style={[BoxStyles.borderBox]}>
                  <View style={[BoxStyles.left,BoxStyles.bgred]} >
                    <Text style={BoxStyles.yellow}>left</Text></View>
                  <View style={[BoxStyles.box,BoxStyles.height300]}>
                    <View style={[BoxStyles.top,BoxStyles.height50,BoxStyles.bggreen]}>
                      <Text style={BoxStyles.yellow}>top</Text></View>
                    <View style={[BoxStyles.paddingBox]}>
                      <View style={[BoxStyles.left,BoxStyles.bggreen]} >
                        <Text style={BoxStyles.yellow}>left</Text></View>
                      <View style={[BoxStyles.box,BoxStyles.height200]}>
                        <View style={[BoxStyles.top,BoxStyles.height50,BoxStyles.bgyellow]}>
                          <Text style={BoxStyles.yellow}>top</Text></View>
                        <View style={[BoxStyles.elementBox]}>
                          <View style={[BoxStyles.left,BoxStyles.bgyellow]} >
                            <Text style={BoxStyles.yellow}>left</Text></View>
                          <View style={[BoxStyles.box,BoxStyles.height100]}>
                            <View  style={[BoxStyles.label]}>
                              <Text style={BoxStyles.white}>element</Text></View>
                            <View style={[BoxStyles.widthdashed]} ></View>
                            <View style={[BoxStyles.heightdashed]} ></View>
                            <View style={[BoxStyles.measureBox]} >
                              <View style={[BoxStyles.right]}>
                                <Text style={[BoxStyles.yellow]}>height</Text></View>
                            </View>
                            <View style={[BoxStyles.bottom,BoxStyles.height50]}>
                              <Text style={BoxStyles.yellow}>width</Text></View>
                          </View>
                          <View style={[BoxStyles.right,BoxStyles.bgyellow]}><Text style={BoxStyles.yellow}>right</Text></View>
                        </View>
                        <View style={[BoxStyles.bottom,BoxStyles.height50,BoxStyles.bgyellow]}>
                          <Text style={BoxStyles.yellow}>bottom</Text></View>
                        <View style={[BoxStyles.label]}>
                          <Text style={BoxStyles.white}>padding</Text></View>
                      </View>
                      <View style={[BoxStyles.right,BoxStyles.bggreen]}><Text style={BoxStyles.yellow}>right</Text></View>
                    </View>
                    <View style={[BoxStyles.bottom,BoxStyles.height50,BoxStyles.bggreen]}>
                      <Text style={BoxStyles.yellow}>bottom</Text></View>
                    <View style={[BoxStyles.label]}><Text style={BoxStyles.white}>border</Text></View>
                  </View>
                  <View style={[BoxStyles.right,BoxStyles.bgred]}>
                    <Text style={BoxStyles.yellow}>right</Text></View>
                </View>
                <View style={[BoxStyles.bottom,BoxStyles.height50,BoxStyles.bgred]}>
                  <Text style={BoxStyles.yellow}>bottom</Text></View>
                <View style={[BoxStyles.label]} ><Text style={BoxStyles.white}>margin</Text></View>
              </View>
            </View>
        );
      }
    }
    
    const BoxStyles = StyleSheet.create({
      height50:{
        height: 50,
      },
      height400:{
        height: 400,
      },
      height300:{
        height: 300,
      },
      height200:{
        height: 200,
      },
      height100:{
        height: 100,
      },
      width400:{
        width: 400,
      },
      width300:{
        width: 300,
      },
      width200:{
        width: 200,
      },
      width100:{
        width: 100,
      },
      bgred: {
        backgroundColor:'#6AC5AC',
      },
      bggreen: {
        backgroundColor: '#414142',
      },
      bgyellow: {
        backgroundColor: '#D64078',
      },
      box: {
        flexDirection: 'column',
        flex: 1,
        position: 'relative',
      },
      label: {
        top: 0,
        left: 0,
        paddingTop: 0,
        paddingRight: 3,
        paddingBottom: 3,
        paddingLeft: 0,
        position: 'absolute',
        backgroundColor: '#FDC72F',
      },
      top: {
        justifyContent: 'center',
        alignItems: 'center',
      },
      bottom: {
        justifyContent: 'center',
        alignItems: 'center',
      },
      right: {
        width: 50,
        justifyContent: 'space-around',
        alignItems: 'center',
      },
      left: {
        width: 50,
        justifyContent: 'space-around',
        alignItems: 'center',
      },
      heightdashed: {
        bottom: 0,
        top: 0,
        right: 20,
        borderLeftWidth: 1,
        position: 'absolute',
        borderLeftColor: '#FDC72F',
      },
      widthdashed: {
        bottom: 25,
        left: 0,
        right: 0,
        borderTopWidth: 1,
        position: 'absolute',
        borderTopColor: '#FDC72F',
      },
      yellow: {
        color: '#FDC72F',
        fontWeight:'900',
      },
      white: {
        color: 'white',
        fontWeight:'900',
      },
      margginBox:{
        position: 'absolute',
        top: 100,
        paddingLeft:7,
        paddingRight:7,
      },
      borderBox:{
        flex: 1,
        justifyContent: 'space-between',
        flexDirection: 'row',
      },
      paddingBox:{
        flex: 1,
        justifyContent: 'space-between',
        flexDirection: 'row',
      },
      elementBox:{
        flex: 1,
        justifyContent: 'space-between',
        flexDirection: 'row',
      },
      measureBox:{
        flex: 1,
        flexDirection: 'row',
        justifyContent: 'flex-end',
        alignItems:'flex-end',
      },
      container: {
        flex: 1,
        justifyContent: 'center',
        alignItems: 'center',
        backgroundColor: '#F5FCFF',
      },
      welcome: {
        fontSize: 20,
        textAlign: 'center',
        margin: 10,
      },
      instructions: {
        textAlign: 'center',
        color: '#333333',
        marginBottom: 5,
      },
    });
    
    AppRegistry.registerComponent('DongFang', () => DongFang);

![这里写图片描述][20160623132609705]

[20160623132351915]: /images/20220721/1a9be9ecd67f4c2bbb5ad8ba5bb8e430.png
[20160623132609705]: /images/20220721/13dfdcd54d4e4c1d8566c959a4d3307b.png