jQuery Drag＆Drop：拖动一个封闭元素

Posted 2021-04-20

我正在尝试根据本指南添加拖放功能

https://www.w3schools.com/HTML/html5_draganddrop.asp

我有

CoffeeScript

  $('#topic-list').on 'dragstart', '.topic-draggable', (event) ->
    console.log event
    event.originalEvent.dataTransfer.setData("text", event.target.id)
    console.log event.target
    console.log event.target.id

html (ERB)

  <li draggable="true" class="topic-draggable" id="topic_{{{topic_id}}}">
    <a href='<%= topics_path %>/{{{topic_id}}}'>

项目是动态插入的，*_id由数字代替。问题是，当我试图拖动<li>，然后event.target是<a>元素，target.id是空白。

Browser console

<a href="/topics/2">
  <i class="fa fa-th"></i>
  <span class="topic-name">Life Span Development</span>
  <i class="fa fa-angle-right"></i>
</a>

如何拖放<li>元素，而不是<a>元素？

我可以使用event.target.parent或一些黑客，但不确定是否正确。我尝试过，但得到了错误Uncaught TypeError: Cannot read property 'parent' of undefined。

$('#topic-list').on('dragstart', '.topic-draggable', function(event) {
  console.log(event);
  event.originalEvent.dataTransfer.setData("text", event.target.id);
  console.log(event.target);
  return console.log(event.target.id);
});

ul#topic-list {
        box-sizing: border-box;
        color: white;
        background-color: #20A0D0;
        list-style: none;
        padding: 0;
        margin: 0;
}
        li {
          list-style: none;
}
          li:nth-child(even) {
            background-color: #3DB1E7;
          }

          a {
            padding: 20px 20px;
            display: flex;
            font-size: 1.4em;
            text-decoration: none;
            color: white;
            justify-content: space-between;
          }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.3.1/css/all.css" integrity="sha384-mzrmE5qonljUremFsqc01SB46JvROS7bZs3IO2EmfFsd15uHvIt+Y8vEf7N7fWAU" crossorigin="anonymous">

<ul id="topic-list" style="display: block;">
  <li draggable="true" class="topic-draggable" id="topic_1">
    <a href="/topics/1">
      <i draggable="true" class="fa fa-th topic-draggable"></i>
      <span class="topic-name">Introduction to A&amp;P</span>
      <i class="fa fa-angle-right"></i>
    </a>
  </li>

  <li draggable="true" class="topic-draggable" id="topic_2">
    <a href="/topics/2">
      <i draggable="true" class="fa fa-th topic-draggable"></i>
      <span class="topic-name">Life Span Development</span>
      <i class="fa fa-angle-right"></i>
    </a>
  </li>

  <li draggable="true" class="topic-draggable" id="topic_3">
    <a href="/topics/3">
      <i draggable="true" class="fa fa-th topic-draggable"></i>
      <span class="topic-name">Medical Terminology</span>
      <i class="fa fa-angle-right"></i>
    </a>
  </li>

</ul>

我实际上无法创建一个例子，因为StackOverflow的代码编辑器给出了错误DOMException: Blocked a frame with origin "null" from accessing a cross-origin frame.。

答案

好吧，我终于惊慌失措了。

CoffeeScript

  topicDrag = false
  currentTarget = null
  $('#topic-list').on 'dragstart', '.topic-draggable', (event) ->
    li = $(event.target).parent().parent()
    event.originalEvent.dataTransfer.setData("text", li.attr('id'))
    li.css('border', '1px dashed red').css('opacity', '0.3')
    topicDrag = true

  $('#topic-list').on 'dragover', 'li', (event) ->
    event.preventDefault() if topicDrag # allow drop, but only for our topics, not random links

  $('#topic-list').on 'dragenter', 'li', (event) ->
    return unless topicDrag
    # browser will call dragleave after dragenter when moving from one <li> to another, turning off the border. fix order.
    currentTarget = event.target # save only the very last target
    setTimeout ->
      # console.log 'dragenter '+currentTarget.nodeName
      $(currentTarget).parentsUntil('#topic-list', 'li').css('border', '2px dashed yellow')
    , 100

  $('#topic-list').on 'dragleave', 'li', (event) ->
    # console.log 'dragleave '+event.target.nodeName
    # when jumping from li > a > span to another, browser calls events in wrong order. clear all.
    $('#topic-list').children().css('border', 'initial')

  $('#topic-list').on 'drop', 'li', (event) ->
    event.preventDefault()
    data = event.originalEvent.dataTransfer.getData("text")
    # console.log data
    source = $('#'+data)
    # the browser allows dropping on child elements of <li> for some reason
    $(event.target).parentsUntil('#topic-list', 'li').before( source ).css('border', 'initial')
    source.css('opacity', 'initial').css('border', 'initial')
    topicDrag = false

HTML-ERB

  <li id="topic_{{{topic_id}}}">
    <a href='<%= topics_path %>/{{{topic_id}}}'>
      <%= fa_icon 'th', draggable: true, class: 'topic-draggable' %>
      <span class='topic-name'>{{{topic_name}}}</span>
      <%= fa_icon "angle-right" %>
    </a>
  </li>