详细分析React 表单与事件

本章节我们将讨论如何在 React 中使用表单。

HTML 表单元素与 React 中的其他 DOM 元素有所不同,因为表单元素生来就保留一些内部状态。

在 HTML 当中，像 , , 和 <select> 这类表单元素会维持自身状态，并根据用户输入进行更新。但在React中，可变的状态通常保存在组件的状态属性中，并且只能用 setState() 方法进行更新。</p> <p><strong>一个简单的实例</strong></p> <p>在实例中我们设置了输入框 input 值 value = {this.state.data}。在输入框值发生变化时我们可以更新 state。我们可以使用 onChange 事件来监听 input 的变化，并修改 state。</p> <pre class="brush:js;"> class HelloMessage extends React.Component { constructor(props) { super(props); this.state = {value: 'Hello jb51!'}; this.handleChange = this.handleChange.bind(this); } handleChange(event) { this.setState({value: event.target.value}); } render() { var value = this.state.value; return <input type="text" value={value} onChange={this.handleChange} /> {value} ; } } ReactDOM.render( <HelloMessage />, document.getElementById('example') );</pre> <p>上面的代码将渲染出一个值为 Hello jb51! 的 input 元素，并通过 onChange 事件响应更新用户输入的值。</p> <p><strong>实例 2<br /> </strong></p> <p>在以下实例中我们将为大家演示如何在子组件上使用表单。 onChange 方法将触发 state 的更新并将更新的值传递到子组件的输入框的 value 上来重新渲染界面。</p> <p>你需要在父组件通过创建事件句柄 (handleChange) ，并作为 prop (updateStateProp) 传递到你的子组件上。</p> <pre class="brush:js;"> class Content extends React.Component { render() { return <input type="text" value={this.props.myDataProp} onChange={this.props.updateStateProp} /> {this.props.myDataProp} ; } } class HelloMessage extends React.Component { constructor(props) { super(props); this.state = {value: 'Hello jb51!'}; this.handleChange = this.handleChange.bind(this); } handleChange(event) { this.setState({value: event.target.value}); } render() { var value = this.state.value; return <Content myDataProp = {value} updateStateProp = {this.handleChange}></Content> ; } } ReactDOM.render( <HelloMessage />, document.getElementById('example') );</pre> <p>运行结果</p> <p style="text-align: center"></p> <p><strong>Select 下拉菜单</strong></p> <p>在 React 中，不使用 selected 属性，而在根 select 标签上用 value 属性来表示选中项。</p> <pre class="brush:js;"> class FlavorForm extends React.Component { constructor(props) { super(props); this.state = {value: 'coconut'}; this.handleChange = this.handleChange.bind(this); this.handleSubmit = this.handleSubmit.bind(this); } handleChange(event) { this.setState({value: event.target.value}); } handleSubmit(event) { alert('Your favorite flavor is: ' + this.state.value); event.preventDefault(); } render() { return ( ); } } ReactDOM.render( <FlavorForm />, document.getElementById('example') );</pre> <p>运行结果</p> <p style="text-align: center"></p> <p><strong>多个表单<br /> </strong></p> <p>当你有处理多个 input 元素时，你可以通过给每个元素添加一个 name 属性，来让处理函数根据 event.target.name 的值来选择做什么。</p> <pre class="brush:js;"> class Reservation extends React.Component { constructor(props) { super(props); this.state = { isGoing: true, numberOfGuests: 2 }; this.handleInputChange = this.handleInputChange.bind(this); } handleInputChange(event) { const target = event.target; const value = target.type === 'checkbox' ? target.checked : target.value; const name = target.name; this.setState({ [name]: value }); } render() { return ( ); } }</pre> <p>输出结果</p> <p style="text-align: center"></p> <p><strong>React 事件</strong></p> <p>以下实例演示通过 onClick 事件来修改数据：</p> <pre class="brush:js;"> class HelloMessage extends React.Component { constructor(props) { super(props); this.state = {value: 'Hello jb51!'}; this.handleChange = this.handleChange.bind(this); } handleChange(event) { this.setState({value: '考高分网'}) } render() { var value = this.state.value; return <button onClick={this.handleChange}>点我</button> {value} ; } } ReactDOM.render( <HelloMessage />, document.getElementById('example') );</pre> <p>当你需要从子组件中更新父组件的 state 时，你需要在父组件通过创建事件句柄 (handleChange) ，并作为 prop (updateStateProp) 传递到你的子组件上。实例如下：</p> <pre class="brush:js;"> class Content extends React.Component { render() { return <button onClick = {this.props.updateStateProp}>点我</button> {this.props.myDataProp} } } class HelloMessage extends React.Component { constructor(props) { super(props); this.state = {value: 'Hello jb51!'}; this.handleChange = this.handleChange.bind(this); } handleChange(event) { this.setState({value: '考高分网'}) } render() { var value = this.state.value; return <Content myDataProp = {value} updateStateProp = {this.handleChange}></Content> ; } } ReactDOM.render( <HelloMessage />, document.getElementById('example') );</pre> <p>运行结果</p> <p style="text-align: center"></p> <p>以上就是详细分析React 表单与事件的详细内容，更多关于React 表单与事件的资料请关注考高分网其它相关文章！</p></div> </div> <div style="clear: both;"></div> <div class="author-info fl"> <div><span class="gray">转载请注明：</span>文章转载自 <a href="https://www.mshxw.com/" class="blue">www.mshxw.com</a></div> <div><span class="gray">本文地址：</span><a href="https://www.mshxw.com/it/69754.html" class="blue">https://www.mshxw.com/it/69754.html</a></div> </div> <div class="prev fl"> <p> <a style='text-align:left;' class='center-block text-center glyphicon glyphicon-collapse-down' href="https://www.mshxw.com/it/69753.html">上一篇 jQuery 动态粒子效果示例代码</a> </p> <p> <a style='text-align:left;' class='center-block text-center glyphicon glyphicon-collapse-down' href="https://www.mshxw.com/it/69755.html">下一篇详解React 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