使用HTML，JS和CSS只需点击一个下拉面板 [英] Have only one drop down panel open on click using HTML, JS, and CSS

问题描述

我有一个固定在我正在尝试构建的网页左侧的链接的下拉菜单列表。我在W3学校获得了HTML和CSS 这里的结构，但适合我的网页。我喜欢它的出现方式，因为它是打开面板以显示链接的平滑过渡，但是因为它是固定的，如果所有下拉面板均打开，则无法向下滚动屏幕以查看。我原本希望如果它变得太长，就会滚动它，但我宁愿拥有它，一次只能打开一个下拉面板。我希望像这里的功能，我仍然保持平稳过渡开闭面板。我还在学习，所以我不知道如何修改代码来做我想做的事情，所以我希望有人能帮助我。我想坚持只用HTML，JS和CSS。以下是我在页面中使用的核心部分。

I have a drop down menu list of links fixed on the left side of a web page I'm trying to build. I got the structure of the HTML and CSS here on w3 schools, but fit it to my page. I like the way it came out because it's a smooth transition of opening the panel to show the links, however because it's fixed, if all the drop down panels are open you can't scroll down the screen to see. I originally wanted to have it scroll if it became too long, but I would much rather have it where only one drop down panel is open at a time. I would like that functionality like here where I still keep the smooth transition of opening and closing panels. I'm still learning, so I don't know how to modify the code to do what I want so I was hoping someone can help me. I would like to stick with just HTML, JS, and CSS. Here's the core pieces I'm using in my page.

CSS

ul {position: fixed;}

li {
    text-align: left;
    display: block;
    text-decoration: none;
}

li.drop-down {
    cursor: pointer;
    transition: 0s;
}

div.drop-down-panel {
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.5s ease-out;
}

a.panel {
    text-align: left;
    display: block;
    text-decoration: none;
}

HTML

<ul>
<li class="drop-down">Header 1</li>
<div class="drop-down-panel">
    <a class="panel" href="#link1">Link 1</a>
    <a class="panel" href="#link2">Link 2</a>
</div>
<li class="drop-down">Header 2</li>
<div class="drop-down-panel">
    <a class="panel" href="#link3">Link 3</a>
</div>
<li class="drop-down">Header 3</li>
<div class="drop-down-panel">
    <a class="panel" href="#link4">Link 4</a>
    <a class="panel" href="#link5">Link 5</a>
</div>
</ul>

JS

var acc = document.getElementsByClassName("drop-down");

for (i = 0; i < acc.length; i++) {
  acc[i].onclick = function() {
    this.classList.toggle("active");
    var panel = this.nextElementSibling;
    if (panel.style.maxHeight){
      panel.style.maxHeight = null;
    } else {
      panel.style.maxHeight = panel.scrollHeight + "px";
    } 
  }
}

推荐答案

希望这有助于：

Hope this helps:

<script>
   var acc = document.getElementsByClassName("drop-down");

    for (i = 0; i < acc.length; i++) {
        acc[i].onclick = function() {
            var panel = this.nextElementSibling;
            var maxHeight = panel.style.maxHeight;

            //Collapse all divs first
            var divs = document.getElementsByClassName("drop-down-panel");
            for (i = 0; i < divs.length; i++) {
                 divs[i].style.maxHeight = null;
            };

            if (maxHeight)
                panel.style.maxHeight = null;
            else
                panel.style.maxHeight = panel.scrollHeight + "px"; 
        }
    }
</script>

基于来自@Mr的评论更新了代码。 Bungle

Updated code based on comment from @Mr. Bungle

<script type="text/javascript">
   var acc = document.getElementsByClassName("drop-down");

    for (i = 0; i < acc.length; i++) {
        acc[i].onclick = function() {
            var panel = this.nextElementSibling;
            var maxHeight = panel.style.maxHeight;

            //Collapse all divs first
            var divs = document.getElementsByClassName("drop-down-panel");
            for (i = 0; i < divs.length; i++) {
                divs[i].style.maxHeight = null;
                divs[i].previousElementSibling.classList.remove("active");  //new code to remove "active" class for all headers (li tags)
            };

            this.classList.toggle("active");  //Moved this line from top

            if (maxHeight)
            {
                panel.style.maxHeight = null;
                this.classList.remove("active"); //Added this line to remove "active" class for the current header
            }
            else
                panel.style.maxHeight = panel.scrollHeight + "px"; 
        }
    } 
</script>

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