一直滚动到div的末尾时，无限滚动不起作用

Question

我正在尝试在聊天中进行无限滚动。我正在使用滚动事件来检查是否scrolltop < clientHeight，并调用函数loadMore。只要您从不滚动到最上端，此效果就很好。我制作了一个gif来显示这一点（希望这很有意义）：

如果在加载较旧的消息时仍然有更多的滚动空间，请保留位置，并向下滚动滚动条。

但是，如果在加载较旧的消息时一直滚动到顶部，则滚动条将始终固定在顶部，并且您会丢失位置（滚动事件也不会触发，因此除非您向下滚动一点）

还有其他人经历过吗？您做了什么修复？任何建议表示赞赏。谢谢！

Answer 1

更新了答案，以支持2个方向（向上或向下）和加载填充。请在扩展模式下运行该代码段，因为内联预览框对于可滚动列表而言太小。

var isLoadingAlready = false;
var upDirection = true; // to load records on top of the list; false to load them to the end of the list
var loadThreshold = 100; // distance to the edge (in pixels) to start loading
var howManyDataLoadsAvailable = 5;

if (upDirection){
    $('.scroll')[0].scrollTop = 100000; // scrolling all the way down
    $('.scroll').css('paddingTop', loadThreshold);
} else {
    $('.scroll').css('paddingBottom', loadThreshold);
}

$('.scroll').on('scroll', function () {
    var s = this; // picking DOM element

    if (s) { // just to be sure/safe
        var scrollableHeight = s.scrollHeight - s.clientHeight;
        if (scrollableHeight > 0) {
            var scrollTop = s.scrollTop;
            var distToTheEdge = upDirection?scrollTop:scrollableHeight - scrollTop;
            if (distToTheEdge < loadThreshold && !isLoadingAlready) {
                isLoadingAlready = true;
                loadMoreRecords(function () { // assuming you have a callback to allow next loading
                    isLoadingAlready = false;
                });
            }
        }
    }
});

loadMoreRecords();

function loadMoreRecords(doneCallback){
    $('.scroll').addClass('loading');

    // simulating the actual loading process with setTimeout
    setTimeout(function(){
        // simulated items to insert:
        var items = [];
        if (howManyDataLoadsAvailable-- > 0){
            for (var i = 0; i < 10; i++){
                items.push($('<li>').text('msg: '+(i+1)+', parts left: '+howManyDataLoadsAvailable));
            }
        }

        var $se = $('.scroll'); // scrollable DOM element
        var $ul = $('.scroll ul');
        var se = $se[0];
        if (upDirection) {
            var hBefore = $ul.height();
            $ul.prepend(items);
            var hDiff = $ul.height() - hBefore;
            se.scrollTop = Math.max(hDiff, loadThreshold);
        } else {
            $ul.append(items);
            se.scrollTop = se.scrollHeight - se.clientHeight - Math.max(se.scrollHeight - se.clientHeight - se.scrollTop, loadThreshold);
        }
        $se.removeClass('loading');
        if (typeof(doneCallback) === 'function'){
            doneCallback();
        }
    }, 500);
}

.scroll{
  overflow-y: auto;
  max-height: 200px;
  border: 2px dashed #aaa;
  padding: 0.5em;
  margin: 1em;
}
.scroll.loading{
  background-color: #f5f5f5;
}

ul{
  list-style: none;
  padding: 0;
}

li{
  padding: 0.5em;
  border: 1px solid #eee;
  border-radius: 0.5em;
  margin: 0.2em;
  animation: colorchange 1200ms;
  background: white;
  box-shadow: 1px 1px 5px 0px rgba(0,0,0,0.05);
}


@keyframes colorchange
{
  0%   {background: #def;}
  100% {background: white;}
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>

<div class="scroll">
  <ul></ul>
</div>