使用react 实现拖拽功能

初心始现 發表於 2020-11-11 11:14:00

<h3>一、关于拖动</h3>
图片默认可以拖动，其他元素的拖动效果同图片。正常的 div 是不能被拖动的，鼠标点击选择后移动没有效果，需要加 draggable="true" 使得元素可以被拖动。
<h3>二、拖拽相关的几个事件</h3>
被拖拽元素的事件：ondragstart，ondragend 
放置元素的事件：ondragenter、ondragover、ondragleave、ondrop 
顾名思义，不需要解释。
需要注意是 ondragover 的默认事件 Reset the current drag operation to "none". 所以想让一个元素可放置，需要重写 ondragover 
<div class="cnblogs_code" style="margin-left: 30px">
<pre>element.ondragover = event => {
event.preventDefault();
// ...
}</pre>
</div>
当一个元素是可放置的，拖拽经过时鼠标会变成加号（cursor: copy;）<img src="https://img2020.cnblogs.com/blog/1895520/202011/1895520-20201111110222481-607359219.png" alt="" width="14" height="13" loading="lazy">
 有一个对象 dataTransfer 可以用来存储拖拽数据。
<div class="cnblogs_code" style="margin-left: 30px">
<pre>dragEle.ondragstart = e => e.dataTransfer.setData('item', e.target.id);</pre>
</div>
拖拽开始时触发，把被拖拽元素的 id 存入  e.dataTransfer 
然后在 ondrop 的时候可以获取到这个值（ondragenter、ondragover、ondragleave 获取不到...）
<div class="cnblogs_code" style="margin-left: 30px">
<pre>putEle.ondrop = function(e) {
let id = e.dataTransfer.getData('item');
// ...
}</pre>
</div>
<h3> 三、react中使用代码演示 [点击查看演示]</h3>
 
<div class="cnblogs_code" style="margin-left: 30px">
<pre><!DOCTYPE html>
<html>
<head>
 <meta charset="utf-8">
 <title></title>
 <script src="https://unpkg.com/react@16/umd/react.development.js"></script>
 <script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
 <script src="https://unpkg.com/babel-standalone@6.15.0/babel.min.js"></script>
 <style>
 .item {
 border: 1px solid #1da921;
 width: 180px;
 border-radius: 5px;
 box-shadow: 0 0 5px 0 #b3b3b3;
 margin: 5px auto;
 background: #fff;
 }
 .item.active {
 border-style: dashed;
 }
 .item-header {
 font-size: 12px;
 color: #9e9e9e;
 padding: 3px 5px;
 }
 .item-main {
 padding: 5px;
 font-size: 14px;
 color: #424242;
 height: 36px;
 overflow: hidden;
 text-overflow: ellipsis;
 display: -webkit-box;
 -webkit-box-orient: vertical;
 -webkit-line-clamp: 2;
 }
 .item-header-point {
 background: #ccc;
 float: right;
 padding: 0 4px;
 min-width: 10px;
 text-align: center;
 color: #fff;
 border-radius: 50%;
 }
 .col {
 border: 1px solid #d2d2d2;
 flex-grow: 1;
 width: 180px;
 height: 100%;
 margin: 0 2px;
 background: #eee;
 flex-grow: 1;
 display: flex;
 flex-direction: column;
 }
 .col-header {
 height: 40px;
 line-height: 40px;
 background: #1DA921;
 color: #fff;
 text-align: center;
 }
 .col-main {
 overflow: auto;
 flex-grow: 1;
 }
 .col-main.active {
 background: #00ad23;
 opacity: 0.1;
 }
 .task-wrapper {
 display: flex;
 height: 400px;
 width: 700px;
 }
 </style>
</head>
<body>
 <div id="app"></div>
 <script type="text/babel">
 const STATUS_TODO = 'STATUS_TODO';
 const STATUS_DOING = 'STATUS_DOING';
 const STATUS_DONE = 'STATUS_DONE';

 const STATUS_CODE = {
 STATUS_TODO: '待处理',
 STATUS_DOING: '进行中',
 STATUS_DONE: '已完成'
 }
 let tasks = [{
 id: 0,
 status: STATUS_TODO,
 title: '每周七天阅读五次，每次阅读完要做100字的读书笔记',
 username: '小夏',
 point: 10
 }, {
 id: 1,
 status: STATUS_TODO,
 title: '每周七天健身4次，每次健身时间需要大于20分钟',
 username: '橘子🍊',
 point: 5
 }, {
 id: 2,
 status: STATUS_TODO,
 title: '单词*100',
 username: '┑(￣Д ￣)┍',
 point: 2
 }, {
 id: 3,
 status: STATUS_TODO,
 title: '单词*150',
 username: '┑(￣Д ￣)┍',
 point: 2
 }, {
 id: 4,
 status: STATUS_TODO,
 title: '单词*200',
 username: '┑(￣Д ￣)┍',
 point: 2
 }, {
 id: 5,
 status: STATUS_TODO,
 title: '单词*250',
 username: '┑(￣Д ￣)┍',
 point: 2
 }]

 class TaskItem extends React.Component {
 handleDragStart = (e) => {
 this.props.onDragStart(this.props.id);
 }
 render() {
 let { id, title, point, username, active, onDragEnd } = this.props;
 return (
 <div
 onDragStart={this.handleDragStart}
 onDragEnd={onDragEnd}
 id={`item-${id}`}
 className={'item' + (active ? ' active' : '')}
 draggable="true"
 >
 <header className="item-header">
 {username}
 {point}
 </header>
 <main className="item-main">{title}</main>
 </div>
 );
 }
 }

 class TaskCol extends React.Component {
 state = {
 in: false
 }
 handleDragEnter = (e) => {
 e.preventDefault();
 if (this.props.canDragIn) {
 this.setState({
 in: true
 })
 }
 }
 handleDragLeave = (e) => {
 e.preventDefault();
 if (this.props.canDragIn) {
 this.setState({
 in: false
 })
 }
 }
 handleDrop = (e) => {
 e.preventDefault();
 this.props.dragTo(this.props.status);
 this.setState({
 in: false
 })
 }
 render() {
 let { status, children } = this.props;
 return (
 <div
 id={`col-${status}`}
 className={'col'}
 onDragEnter={this.handleDragEnter}
 onDragLeave={this.handleDragLeave}
 onDragOver={this.handleDragEnter}
 onDrop={this.handleDrop}
 draggable="true"
 >
 <header className="col-header">
 {STATUS_CODE}
 </header>
 <main className={'col-main' + (this.state.in ? ' active' : '')}>
 {children}
 </main>
 </div>
 );
 }
 }

 class App extends React.Component {
 state = {
 tasks: tasks,
 activeId: null
 }
 /**
 * 传入被拖拽任务项的 id
 */
 onDragStart = (id) => {
 this.setState({
 activeId: id
 })
 }

 dragTo = (status) => {
 let { tasks,activeId} = this.state;
 let task = tasks;
 if (task.status !== status) {
 task.status = status;
 this.setState({
 tasks: tasks
 })
 }
 this.cancelSelect();
 }

 cancelSelect = () => {
 this.setState({
 activeId: null
 })
 }

 render() {
 let { tasks, activeId } = this.state;
 let { onDragStart, onDragEnd, cancelSelect } = this;
 return (
 <div className="task-wrapper">
 {
 Object.keys(STATUS_CODE).map(status =>
 <TaskCol
 status={status}
 key={status}
 dragTo={this.dragTo}
 canDragIn={activeId != null && tasks.status !== status}>
 { tasks.filter(t => t.status === status).map(t =>
 <TaskItem
 key={t.id}
 active={t.id === activeId}
 id={t.id}
 title={t.title}
 point={t.point}
 username={t.username}
 onDragStart={onDragStart}
 onDragEnd={cancelSelect}
 />)
 }
 </TaskCol>
 )
 }
 </div>
 )
 }
 }

 ReactDOM.render(
 <App />,
 document.getElementById('app')
 );
 </script>
</body>
</html></pre>
</div>
<h3>四、效果</h3>
<img src="https://img2020.cnblogs.com/blog/1895520/202011/1895520-20201111111350101-388729124.png" alt="" loading="lazy">
<h3>四、演示地址：</h3>
　　查看演示
 
<h3>五、原文来源</h3>
　　【我不吃饼干呀】 的博客文章 
来源：https://www.cnblogs.com/art-poet/p/13957728.html

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使用react 实现拖拽功能