React 实现拖拽功能
实现效果：（可戳 https://codepen.io/wenr/pen/EGEQxp 查看）
因为工作中会用到 JIRA 所以想实现一下相似的功能，顺便学习一下 H5 的拖拽。不支持拖拽改变顺序，感觉有点麻烦，而且没必要。感觉相关的博文好少的，大部分都是直接上代码，没有解释。
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。
拖拽相关的几个事件，有被拖动元素的事件，也有拖动进入的容器元素的事件。
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
element.ondragover = event => { event.preventDefault(); // ... }
当一个元素是可放置的，拖拽经过时鼠标会变成加号（cursor: copy;）
有一个对象 dataTransfer 可以用来存储拖拽数据。
dragEle.ondragstart = e => e.dataTransfer.setData('item', e.target.id);
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...）
putEle.ondrop = function(e) { let id = e.dataTransfer.getData('item'); // ... }
简单的应用：
<!DOCTYPE html> <html lang="zh"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>Document</title> <style> .wrapper {display: flex;border: 1px solid orangered;padding: 10px;} .col {border: 1px solid #808080;height: 500px;width: 200px;margin: 0 10px;padding: 10px;} .item {border: 1px solid #808080;margin: 5px 0;} </style> </head> <body> <div class="wrapper"> <div class="col1 col"> <div class="item" id="item1" draggable="true">item1</div> <div class="item" id="item2" draggable="true">item2</div> <div class="item" id="item3" draggable="true">item3</div> </div> <div class="col2 col"></div> <div class="col3 col"></div> <div class="col4 col"></div> </div> <script> let cols = document.getElementsByClassName('col'); for (let col of cols) { col.ondragenter = e => { console.log('放置元素 ondragenter', '<' + e.dataTransfer.getData('item') + '>'); } col.ondragover = e => { e.preventDefault(); console.log('放置元素 ondragover', '<' + e.dataTransfer.getData('item') + '>'); } col.ondragleave = e => { console.log('放置元素 ondragleave', '<' + e.dataTransfer.getData('item') + '>'); } col.ondrop = function(e) { console.log('放置元素 ondrop', '<' + e.dataTransfer.getData('item') + '>'); this.append(document.getElementById(e.dataTransfer.getData('item'))); } } let items = document.getElementsByClassName('item'); for (let item of items) { item.ondragstart = e => { console.log('拖拽元素 ondragstart'); e.dataTransfer.setData('item', e.target.id); } item.ondragend = e => { console.log('拖拽元素 ondragend'); } } </script> </body> </html>
文章开头部分的 React 写的 demo
<!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-${id}`} className={'item' + (active ? ' active' : '')} draggable="true" > <header className="item-header"> <span className="item-header-username">{username}</span> <span className="item-header-point">{point}</span> </header> <main className="item-main">{title}</main> </div> ); } } class TaskCol extends React.Component { state = { in: false } handleDragEnter = (e) => { e.preventDefault(); if (this.props.canDragIn) { this.setState({ in: true }) } } handleDragLeave = (e) => { e.preventDefault(); if (this.props.canDragIn) { this.setState({ in: false }) } } handleDrop = (e) => { e.preventDefault(); this.props.dragTo(this.props.status); this.setState({ in: false }) } render() { let { status, children } = this.props; return ( <div id={`col-${status}`} className={'col'} onDragEnter={this.handleDragEnter} onDragLeave={this.handleDragLeave} onDragOver={this.handleDragEnter} onDrop={this.handleDrop} draggable="true" > <header className="col-header"> {STATUS_CODE[status]} </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[activeId]; 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[activeId].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>
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