我遇到的问题是,一个元素的dragleave事件是在悬停该元素的子元素时触发的。同样,当再次悬停回父元素时,dragenter不会被触发。

我做了一个简化的小提琴:http://jsfiddle.net/pimvdb/HU6Mk/1/。

HTML:

<div id="drag" draggable="true">drag me</div>

<hr>

<div id="drop">
    drop here
    <p>child</p>
    parent
</div>

使用以下JavaScript:

$('#drop').bind({
                 dragenter: function() {
                     $(this).addClass('red');
                 },

                 dragleave: function() {
                     $(this).removeClass('red');
                 }
                });

$('#drag').bind({
                 dragstart: function(e) {
                     e.allowedEffect = "copy";
                     e.setData("text/plain", "test");
                 }
                });

它应该做的是,当拖拽一些东西时,通过将drop div设置为红色来通知用户。这是可行的,但是如果你拖动到p子元素中,拖动键就会触发,div就不再是红色了。移动回下拉div也不会使它再次变红。有必要完全移出拖放div,并再次拖回它,使其变为红色。

是否有可能阻止dragleave在拖动到子元素时发射?

2017年更新:TL;DR,查找CSS指针事件:无;如@ h.d.所述。在现代浏览器和IE11中都能运行。


当前回答

我在这个问题上挣扎了很多,即使在读完所有这些答案之后,我想我可以和你分享我的解决方案,因为我认为这可能是一种更简单的方法,尽管有点不同。我的想法是简单地完全省略dragleave事件监听器,并在每个新的dragenter事件触发时编码dragleave行为,同时确保dragenter事件不会被不必要地触发。

在下面的例子中,我有一个表,我希望能够通过拖放API相互交换表行内容。在dragenter上,一个CSS类将被添加到当前拖动元素的row元素中,以突出显示它,而在dragleave上,这个类将被删除。

例子:

非常基本的HTML表格:

<table>
  <tr>
    <td draggable="true" class="table-cell">Hello</td>
  </tr>
  <tr>
    <td draggable="true" clas="table-cell">There</td>
  </tr>
</table>

还有dragenter事件处理函数,添加到每个表格单元格中(除了dragstart, dragover, drop和dragend处理程序,它们不是针对这个问题的,所以这里不复制):

/*##############################################################################
##                              Dragenter Handler                             ##
##############################################################################*/

// When dragging over the text node of a table cell (the text in a table cell),
// while previously being over the table cell element, the dragleave event gets
// fired, which stops the highlighting of the currently dragged cell. To avoid
// this problem and any coding around to fight it, everything has been
// programmed with the dragenter event handler only; no more dragleave needed

// For the dragenter event, e.target corresponds to the element into which the
// drag enters. This fact has been used to program the code as follows:

var previousRow = null;

function handleDragEnter(e) {
  // Assure that dragenter code is only executed when entering an element (and
  // for example not when entering a text node)
  if (e.target.nodeType === 1) {
    // Get the currently entered row
    let currentRow = this.closest('tr');
    // Check if the currently entered row is different from the row entered via
    // the last drag
    if (previousRow !== null) {
      if (currentRow !== previousRow) {
        // If so, remove the class responsible for highlighting it via CSS from
        // it
        previousRow.className = "";
      }
    }
    // Each time an HTML element is entered, add the class responsible for
    // highlighting it via CSS onto its containing row (or onto itself, if row)
    currentRow.className = "ready-for-drop";
    // To know which row has been the last one entered when this function will
    // be called again, assign the previousRow variable of the global scope onto
    // the currentRow from this function run
    previousRow = currentRow;
  }
}

在代码中留下非常基本的注释,因此这段代码也适合初学者。希望这对你有所帮助!请注意,您当然需要将我上面提到的所有事件侦听器添加到每个表单元格中,这样才能工作。

其他回答

我也遇到过同样的问题,下面是我的解决方案——我认为比上面的要简单得多。我不确定它是否跨浏览器(可能取决于冒泡顺序)

为了简单起见,我将使用jQuery,但解决方案应该是框架独立的。

事件以任意一种方式生成父节点,如下所示:

<div class="parent">Parent <span>Child</span></div>

我们附加事件

el = $('.parent')
setHover = function(){ el.addClass('hovered') }
onEnter  = function(){ setTimeout(setHover, 1) }
onLeave  = function(){ el.removeClass('hovered') } 
$('.parent').bind('dragenter', onEnter).bind('dragleave', onLeave)

差不多就是这样。:)它可以工作,因为即使onEnter在子上先于onLeave在父上触发,我们延迟它稍微颠倒顺序,所以类先被删除,然后在一毫秒后重新应用。

你可以在Firefox中使用jQuery源代码来修复它:

dragleave: function(e) {
    var related = e.relatedTarget,
        inside = false;

    if (related !== this) {

        if (related) {
            inside = jQuery.contains(this, related);
        }

        if (!inside) {

            $(this).removeClass('red');
        }
    }

}

不幸的是,它在Chrome中不起作用,因为relatedTarget在dragleave事件上似乎不存在,我假设你在Chrome中工作,因为你的例子在Firefox中不起作用。下面是实现上述代码的一个版本。

我能够做到这一点使用超时dragleave。与其他使用这种方法的答案不同,我认为在拖拽时重置这个超时以避免闪烁是至关重要的。

我写的只是你需要的函数,然后使用你选择的框架进行绑定

let dragoverTimeout;
const onDragOver = (e: Event) => {
  e.preventDefault();
  e.stopPropagation();

  if (dragoverTimeout) {
    window.clearTimeout(dragoverTimeout);
    dragoverTimeout = null;
  }
  // Add your class here
}

const onDragLeave = (e: Event) => {
  e.preventDefault();
  e.stopPropagation();

  if (!dragoverTimeout) {
    dragoverTimeout = window.setTimeout(() => {
      // Remove your class here
    }, 100);
  }
}

const onDrop = (e) => {
  e.preventDefault();
  e.stopPropagation();

  const files = e.dataTransfer.files;
  // Remove your class here

  if (files.length > 0) {
    this.uploadFile(files);
  }
}

我在这个问题上挣扎了很多,即使在读完所有这些答案之后,我想我可以和你分享我的解决方案,因为我认为这可能是一种更简单的方法,尽管有点不同。我的想法是简单地完全省略dragleave事件监听器,并在每个新的dragenter事件触发时编码dragleave行为,同时确保dragenter事件不会被不必要地触发。

在下面的例子中,我有一个表,我希望能够通过拖放API相互交换表行内容。在dragenter上,一个CSS类将被添加到当前拖动元素的row元素中,以突出显示它,而在dragleave上,这个类将被删除。

例子:

非常基本的HTML表格:

<table>
  <tr>
    <td draggable="true" class="table-cell">Hello</td>
  </tr>
  <tr>
    <td draggable="true" clas="table-cell">There</td>
  </tr>
</table>

还有dragenter事件处理函数,添加到每个表格单元格中(除了dragstart, dragover, drop和dragend处理程序,它们不是针对这个问题的,所以这里不复制):

/*##############################################################################
##                              Dragenter Handler                             ##
##############################################################################*/

// When dragging over the text node of a table cell (the text in a table cell),
// while previously being over the table cell element, the dragleave event gets
// fired, which stops the highlighting of the currently dragged cell. To avoid
// this problem and any coding around to fight it, everything has been
// programmed with the dragenter event handler only; no more dragleave needed

// For the dragenter event, e.target corresponds to the element into which the
// drag enters. This fact has been used to program the code as follows:

var previousRow = null;

function handleDragEnter(e) {
  // Assure that dragenter code is only executed when entering an element (and
  // for example not when entering a text node)
  if (e.target.nodeType === 1) {
    // Get the currently entered row
    let currentRow = this.closest('tr');
    // Check if the currently entered row is different from the row entered via
    // the last drag
    if (previousRow !== null) {
      if (currentRow !== previousRow) {
        // If so, remove the class responsible for highlighting it via CSS from
        // it
        previousRow.className = "";
      }
    }
    // Each time an HTML element is entered, add the class responsible for
    // highlighting it via CSS onto its containing row (or onto itself, if row)
    currentRow.className = "ready-for-drop";
    // To know which row has been the last one entered when this function will
    // be called again, assign the previousRow variable of the global scope onto
    // the currentRow from this function run
    previousRow = currentRow;
  }
}

在代码中留下非常基本的注释,因此这段代码也适合初学者。希望这对你有所帮助!请注意,您当然需要将我上面提到的所有事件侦听器添加到每个表单元格中,这样才能工作。

这是我的解决方案(https://jsfiddle.net/42mh0fd5/8):

<div id="droppable">
    <div id="overlay"></div>
    <a href="">test child 1</a>
    <br /><br />
    <button>test child 2</button>
    <br /><br />
    <button>test child 3</button>
    <br />
</div>
<p id="draggable" draggable="true">This element is draggable.</p>


<script type="text/javascript">
var dropElem = document.getElementById('droppable');
var overlayElem = document.getElementById('overlay');

overlayElem.addEventListener('drop', function(ev) {
    ev.preventDefault();
    console.log('drop', ev.dataTransfer.files)
    overlayElem.classList.remove('dragover')
    dropElem.classList.add('dropped')
    console.log('drop')
}, false);

overlayElem.addEventListener('dragover', function(ev) {
    ev.preventDefault();
}, false);

overlayElem.addEventListener('dragleave', function(ev) {
    console.log('dragleave')
    overlayElem.classList.remove('dragover')
}, false);

dropElem.addEventListener('dragenter', function(ev) {
    console.log('dragenter')
    overlayElem.classList.add('dragover')
}, false);
</script>

<style>
#draggable{
    padding:5px;
    background: #fec;
    display: inline-block;
}
#droppable{
    width: 300px;
    background: #eef;
    border: 1px solid #ccd;
    position: relative;
    text-align: center;
    padding:30px;
}
#droppable.dropped{
    background: #fee;
}
#overlay.dragover{
    content:"";
    position: absolute;
    z-index: 1;
    left: 0;
    top: 0;
    right: 0;
    bottom: 0;
    background: rgba(0,0,0,.2);
    border:3px dashed #999;
}
</style>