Multiple drop events in HTML5

问题

I'm trying to create a drag and drop feature in HTML5 where I can drag from one list to another. I have one list with draggable items and another list with items that have drop events added. The problem is, regardless of what element I drop onto, the last drop event that was added is the one that gets called.

Thanks for any help or suggestions.

I've included my code below:

<!DOCTYPE html>

<head>
<title>List Conversion Test</title>

<style type="text/css">

#list, #cart {
  display: inline;
  float: left;
  border: 1px solid #444;
  margin: 25px;
  padding: 10px;
}

#list p {
  background-color: #036;
  color: #fff;
}
#cart p {
  background-color: #363;
  color: #fff;
}

.listitem {

}

.listitem_done {
  text-decoration: line-through;
}

.product {
  background-color: #CCC;
}

.product_over {
  background-color: #363;
}

</style>


<script type="text/javascript" src="http://html5demos.com/js/h5utils.js"></script>

</head>

<body>

<article>
  <div id="list">
    <p>On My List</p>
    <ul>
      <li class="listitem" id="L001">Shopping List Item #1</li>
      <li class="listitem" id="L002">Shopping List Item #2</li>
    </ul>
    <div id="done">
      <p>In My Cart</p>
      <ul></ul>
    </div>
  </div>

  <div id="cart">
    <p>Cart</p>
    <ul>
      <li class="product" id="P001">Product #1</li>
      <li class="product" id="P002">Product #2</li>
    </ul>
  </div>

</article>
<script>

  // make list items draggable
  var list = document.querySelectorAll('li.listitem'), thisItem = null;
  for (var i = 0; i < list.length; i++) {
    thisItem = list[i];

    thisItem.setAttribute('draggable', 'true');

    addEvent(thisItem, 'dragstart', function (e) {
      e.dataTransfer.effectAllowed = 'copy';
      e.dataTransfer.setData('Text', this.id);
    });
  }


  // give products drop events
  var products = document.querySelectorAll('li.product'), thisProduct = null;
  for (var i = 0; i < products.length; i++) {
    thisProduct = products[i];

    addEvent(thisProduct, 'dragover', function (e) {
      if (e.preventDefault) e.preventDefault();
      this.className = 'product_over';
      e.dataTransfer.dropEffect = 'copy';
      return false;
    });

    addEvent(thisProduct, 'dragleave', function () {
     this.className = 'product';
    });

    addEvent(thisProduct, 'drop', function (e) {
      //alert(thisProduct.id);
      if (e.stopPropagation) e.stopPropagation();
      var thisItem = document.getElementById(e.dataTransfer.getData('Text'));
      thisItem.parentNode.removeChild(thisItem);
      thisProduct.className = 'product';
      handleDrop(thisItem, thisProduct);
      return false;
    });

  }

  // handle the drop
  function handleDrop(i, p) {
    alert(i.id + ' to ' + p.id);
    var done = document.querySelector('#done > ul');
    done.appendChild(i);
    i.className = 'listitem_done';
  } 


</script>

</body>
</html>

回答1:

This is why it's often a bad idea to define functions (such as callback functions) within a loop. You're assigning thisProduct within the loop, but it will be reassigned for the next iteration of the loop. The way your closures are set up, each callback is bound to the same variable thisProduct, and will use the latest value.

One possible fix is to create a new closure where thisProduct is needed such as

(function(thisProduct) {
    addEvent(thisProduct, 'drop', function (e) {
      //alert(thisProduct.id);
      if (e.stopPropagation) e.stopPropagation();
      var thisItem = document.getElementById(e.dataTransfer.getData('Text'));
      thisItem.parentNode.removeChild(thisItem);
      thisProduct.className = 'product';
      handleDrop(thisItem, thisProduct);
      return false;
    });
}(thisProduct));

This jsFiddle seems to work for me now. See here for more explanation.

来源：https://stackoverflow.com/questions/6717853/multiple-drop-events-in-html5

标签

javascript

html

drag-and-drop