javascript - 只掉落到可见的元素

Question

我有以下内容:

我正在尝试对其进行设置，以便当您拖动该项目时，它只会掉落到您可以看到的 div 元素，并且不会被掩盖.

所以我用了这个js:

$(".draggable").draggable({
    helper: "clone"
})
$("#bottom, .draggable").droppable({
    drop: function(event, ui) {
        var $this = $(this),
            $dragged = $(ui.draggable);
        $this.append($dragged.clone());
    },
    hoverClass: "dragHover"
})​

但它会在两个位置放置元素，即使只有一个放置区域不可见!

我该如何解决它，以便不会发生这种情况？

fiddle :http://jsfiddle.net/maniator/Wp4LU/

---

重新创建页面的额外信息没有 fiddle :

HTML:

  <div id="top">
    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>

    <div class="draggable">
      Lorem ipsum dolor sit amet
    </div>
  </div>

  <div id="bottom"></div>

CSS:

.draggable {
    border: 1px solid green;
    background: white;
    padding: 5px;
}

.dragHover{
    background: blue;
}

#top {
    height: 500px;
    overflow-y: scroll;
}
#bottom {
    height: 150px;
    overflow-y: scroll;
    border: red solid 4px;
}

Answer 1

尝试使用accept 函数进行设置。 The working demo.

$("#bottom, .draggable").droppable({
    drop: function(event, ui) {
        var $this = $(this),
            $dragged = $(ui.draggable);
        $this.append($dragged.clone());
    },
    accept: function () {
        var $this = $(this), divTop= $("#top");
        if ($this.is(".draggable")) {
          return $this.offset().top < divTop.offset().top + divTop.height() ;
        }
        return true;
    },
    hoverClass: "dragHover"
})​;​