React 实现拖拽功能的示例代码

本文介绍了React 实现拖拽功能的示例代码，分享给大家，具体如下：

实现效果：

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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