React Native入门学习笔记三(JSX语法)

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参考示例:
https://github.com/ruanyf/react-demos

demo1 javascript/babel

很简单,react的jsx语法 与js不同,引用的script标签要这样写:

@H_502_8@<script type="text/babel"></script> @H_502_8@<!DOCTYPE html> <html> <head> <script src="../build/react.js"></script> <script src="../build/react-dom.js"></script> <script src="../build/browser.min.js"></script> </head> <body> <div id="example"></div> <script type="text/babel"> // ** Our code goes here! ** </script> </body> </html>

demo2 简单数组遍历

@H_502_8@var names = ['Alice','Emily','Kate']; ReactDOM.render( <div> { names.map(function (name) { return <div>Hello,{name}!</div> }) } </div>,document.getElementById('example') );

render函数遇到

就按html解析,如果遇到{}就按js解析。

demo3 直接嵌入数组

@H_502_8@var arr = [ <h1>Hello world!</h1>,<h2>React is awesome</h2>,]; ReactDOM.render( <div>{arr}</div>,document.getElementById('example') );

这时会直接展开数组内容

demo4 创建component组件类

使用React.createClass。

@H_502_8@var HelloMessage = React.createClass({ render: function() { return <h1>Hello {this.props.name}</h1>; } }); ReactDOM.render( <HelloMessage name="John" />,document.getElementById('example') );

所有组件类必须有render方法
组件类第一个字母必须大写;
组件类只能有一个顶层标签
组件的属性在组件对象的this.props上获取
this.props.children遍历组件所有子节点;
遍历子节点的示例:

@H_502_8@var NotesList = React.createClass({ render: function() { return ( <ol> { React.Children.map(this.props.children,function (child) { return <li>{child}</li>; }) } </ol> ); } }); ReactDOM.render( <NotesList> <span>hello</span> <span>world</span> </NotesList>,document.body );

子节点可能是undefined/object/array。可以使用React.Children.map遍历子节点避免undefined的情况。

demo05 React.Children.map

@H_502_8@var NotesList = React.createClass({ render: function() { return ( <ol> { React.Children.map(this.props.children,function (child) { return <li>{child}</li>; }) } </ol> ); } }); ReactDOM.render( <NotesList> <span>hello</span> <span>world</span> </NotesList>,document.getElementById('example') );

React.children有另外几种方法
map
forEach
count
only
toArray
可参考:https://facebook.github.io/react/docs/top-level-api.html#react.children

demo06 protoTypes验证

以下示例当title值为数值时,控制台会输出错误

@H_502_8@var MyTitle = React.createClass({ propTypes: { title: React.PropTypes.string.isrequired,},render: function() { return <h1> {this.props.title} </h1>; } });

getDefaultProps设置默认值:

@H_502_8@var MyTitle = React.createClass({ getDefaultProps : function () { return { title : 'Hello World' }; },render: function() { return <h1> {this.props.title} </h1>; } }); ReactDOM.render( <MyTitle />,document.body );

demo07 查找dom

以下示例使用ref查找真实的dom节点。dom节点从虚拟节点到插入到真实dom中时,引用才有效。

@H_502_8@var MyComponent = React.createClass({ handleClick: function() { this.refs.myTextInput.focus(); },render: function() { return ( <div> <input type="text" ref="myTextInput" /> <input type="button" value="Focus the text input" onClick={this.handleClick} /> </div> ); } }); ReactDOM.render( <MyComponent />,document.getElementById('example') );

上面使用了click事件,除此之外,还有react还支持onClick,onKeyDown,onCopy等事件,参考文档:http://facebook.github.io/react/docs/events.html#supported-events

demo08 状态机 this.state

状态机是组件的特殊属性,在值变化时会刷新UI。

@H_502_8@var LikeButton = React.createClass({ getInitialState: function() { return {liked: false}; },handleClick: function(event) { this.setState({liked: !this.state.liked}); },render: function() { var text = this.state.liked ? 'like' : 'haven\'t liked'; return ( <p onClick={this.handleClick}> You {text} this. Click to toggle. </p> ); } }); ReactDOM.render( <LikeButton />,document.getElementById('example') );

demo09 表单

以下示例使用event.target.value获取文本框的值。

@H_502_8@var Input = React.createClass({ getInitialState: function() { return {value: 'Hello!'}; },handleChange: function(event) { this.setState({value: event.target.value}); },render: function () { var value = this.state.value; return ( <div> <input type="text" value={value} onChange={this.handleChange} /> <p>{value}</p> </div> ); } }); ReactDOM.render(<Input/>,document.getElementById('example'));

更多form组件参考:http://facebook.github.io/react/docs/forms.html

demo10 组件生命周期

组件生命周期分为三种状态:

  • Mounting:已插入真实 DOM
  • Updating:正在被重新渲染
  • Unmounting:已移出真实 DOM

以下五个主要事件:

  • componentWillMount()
  • componentDidMount()
  • componentWillUpdate(object nextProps,object nextState)
  • componentDidUpdate(object prevProps,object prevState)
  • componentWillUnmount()

还有两个特殊状态事件:

  • componentWillReceiveProps(object nextProps):已加载组件收到新的参数时调用
  • shouldComponentUpdate(object nextProps,object nextState):组件判断是否重新渲染时调用
@H_502_8@var Hello = React.createClass({ getInitialState: function () { return { opacity: 1.0 }; },componentDidMount: function () { this.timer = setInterval(function () { var opacity = this.state.opacity; opacity -= .05; if (opacity < 0.1) { opacity = 1.0; } this.setState({ opacity: opacity }); }.bind(this),100); },render: function () { return ( <div style={{opacity: this.state.opacity}}> Hello {this.props.name} </div> ); } }); ReactDOM.render( <Hello name="world"/>,document.getElementById('example') );

demo11 ajax

以下示例,使用 componentDidMount 方法设置 Ajax 请求,等到请求成功,再用 this.setState 方法重新渲染 UI 。ajax请求部分使用了jQuery库。

@H_502_8@var UserGist = React.createClass({ getInitialState: function() { return { username: '',lastGistUrl: '' }; },componentDidMount: function() { $.get(this.props.source,function(result) { var lastGist = result[0]; if (this.isMounted()) { this.setState({ username: lastGist.owner.login,lastGistUrl: lastGist.html_url }); } }.bind(this)); },render: function() { return ( <div> {this.state.username}'s last gist is <a href={this.state.lastGistUrl}>here</a>. </div> ); } }); ReactDOM.render( <UserGist source="https://api.github.com/users/octocat/gists" />,document.getElementById('example') );

demo12 promise

下面示例把异步ajax作为组件的属性

@H_502_8@ReactDOM.render( <RepoList promise={$.getJSON('https://api.github.com/search/repositories?q=javascript&sort=stars')} />,document.body );

根据ajax的状态,显示loading,error或结果。

@H_502_8@var RepoList = React.createClass({ getInitialState: function() { return { loading: true,error: null,data: null}; },componentDidMount() { this.props.promise.then( value => this.setState({loading: false,data: value}),error => this.setState({loading: false,error: error})); },render: function() { if (this.state.loading) { return <span>Loading...</span>; } else if (this.state.error !== null) { return <span>Error: {this.state.error.message}</span>; } else { var repos = this.state.data.items; var repoList = repos.map(function (repo) { return ( <li> <a href={repo.html_url}>{repo.name}</a> ({repo.stargazers_count} stars) <br/> {repo.description} </li> ); }); return ( <main> <h1>Most Popular JavaScript Projects in Github</h1> <ol>{repoList}</ol> </main> ); } } });

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