detecting the end of the scrollable drop down

问题

I am generating a select option box dynamically. There can be any number of options. When the user scrolls down to the end of the box, I need to trigger an event, (where I will call the server and populate the select with more options). Its like creating a pagination, but in dropdown box.

Can anybody tell me how can this be done.

So the only thing I need is to trigger an event, when user scrolls to the end of the dropdown. Thats all

<select style="height: 30px;line-height:30px;" class="scroll">
    <option>1</option>
    <option>2</option>
    <option>3</option>
    <option>4</option>
    <option>5</option>
    <option>6</option>
    <option>7</option>
    <option>8</option>
</select>

Please don't worry about how I am gonna populate the select box with option, as I am using meteorJs, that I will achieve it easily.

The only requirement is to fire an event.

回答1:

you can try this one, i have created a demo regarding this and generate a popup while scroll at the bottom of list.

Working fiddle demo: https://jsfiddle.net/j68o44Ld/

<div class="subtask-li">
<span class="main-tlist"> 
<span class="icon-taskListing"></span> 
<span class="subselectedList">Default</span> 
<span class="icon-subcaret"></span> </span>
<ul class="subtask-pick">
<li><a href="javascript:;">General issues</a></li>
<li><a href="javascript:;">Default</a></li>
<li><a href="javascript:;">Android Games Issues</a></li>
<li><a href="javascript:;">pt issues</a></li>
<li><a href="javascript:;">Server Development</a></li>
<li><a href="javascript:;">Resource Integration</a></li>
<li><a href="javascript:;">Server Infrastructure</a></li>
</ul>
    </div>

    $(document).on("click",".main-tlist",function(){
    $('.subtask-pick').toggle();
    });

    $('.subtask-pick').scroll(function () {
          if ($(this)[0].scrollHeight - $(this).scrollTop() <=  $(this).outerHeight()) {
                alert("end of scroll");
              // You can perform as you want

          }
    });



  .subtask-li {
        border: 1px solid #dfe8f1;
        cursor: pointer;
        position: relative;
        background: rgba(0, 0, 0, 0) linear-gradient(to bottom, rgba(255, 255, 255, 1) 0%, rgba(246, 246, 246, 1) 100%) repeat scroll 0 0;
        border-radius: 3px;
        float: left;

        left: 5px;
        padding: 5px;
        top: 6px;
    }


    .subtask-pick{
       background-clip: padding-box;
        background-color: #fff;
        border: 1px solid #dfe8f1;
        border-radius: 3px;
        box-shadow: 0 1px 7px 2px rgba(135, 158, 171, 0.2);
        display: none;
        list-style: outside none none;
        padding: 0 0 10px;
        position: absolute;
        z-index: 9; 
        float: left;
       width: 220px;
        list-style: outside none none; height:220px; overflow:auto;
    }
    .icon-taskListing {
        display: inline-block;
        vertical-align: middle;
    }
    .subselectedList {
        overflow: hidden;
        padding: 0 5px;
        text-overflow: ellipsis;
        white-space: nowrap;
        width: 116px;
    }
    ul.subtask-pick li {
      float: none;
      display: block;
      clear: both;

      position: relative;
    }
    ul.subtask-pick li a {
      padding: .9em 1em .9em .8em;
      position: relative;
        clear: both;
      cursor: pointer;
      display: block;

      white-space: nowrap;
       text-overflow: ellipsis;
      overflow: hidden;
    }
    ul.subtask-pick li a:hover {
      background: none repeat scroll 0 0 #eff4f6;
      cursor: pointer;
    }
    a {
      text-decoration: none;
      outline: 0;
      color: #4c4c4c;
    }

回答2:

There is no way to detect scrolling on an actual select element, so this isn't possible as asked. But you can try creating a custom select-box looking control which is just a scrolling div and apply the feature to it.

UPDATE

DEMO HERE

For the chosen-jquery-plugin you make events listen as below:

This is how the html will be generated from chosen plugin for your select box:

<div class="chosen-container chosen-container-single chosen-container-active" style="width: 100px;" title="">
    <a class="chosen-single" tabindex="-1">
        <span>1</span>
        <div><b></b></div>
    </a>
    <div class="chosen-drop">
        <div class="chosen-search">
            <input type="text" autocomplete="off"/>
        </div>
        <ul class="chosen-results">
            <li class="active-result result-selected" data-option-array-index="0">1</li>
            <li class="active-result" data-option-array-index="1">2</li>
            <li class="active-result" data-option-array-index="2">3</li>
            <li class="active-result" data-option-array-index="3">4</li>
            <li class="active-result" data-option-array-index="4">5</li>
            <li class="active-result" data-option-array-index="5">6</li>
            <li class="active-result" data-option-array-index="6">7</li>
            <li class="active-result" data-option-array-index="7">8</li>
        </ul>
    </div>
</div>

Write a style for .chosen-drop and modify your styles as below and remove inline style from select

.scroll
{
    line-height:30px;
    width:100px;
}

.chosen-drop
{
    overflow-y:scroll;
    max-height: 90px;
}

Your JS would be

$('.chosen-drop').on('scroll',chk_scroll);

function chk_scroll(e)
{
    var elem = $(e.currentTarget);
    console.log(elem[0].scrollHeight-elem.scrollTop());
    console.log(elem.outerHeight());
    if (elem[0].scrollHeight - elem.scrollTop() <= elem.outerHeight()) 
    {
        alert('bottom');
    }
}

来源：https://stackoverflow.com/questions/30797244/detecting-the-end-of-the-scrollable-drop-down