如何让我的下拉菜单显示/对齐

Question

所以我正在创建一个简单的网页，但我不能让我的下拉列表工作正常。此时不再出现，当它出现在水平线而不是垂直线上时。

因为它不显示下拉列表。我错过了什么？我有额外的东西是不需要的吗？

function myFunction() {
document.getElementById("myDropdown").classList.toggle("show");
 }
 window.onclick = function(e) {
if (!e.target.matches('.dropbtn')) {

var dropdowns = document.getElementsByClassName("dropdown-content");
for (var d = 0; d < dropdowns.length; d++) {
  var openDropdown = dropdowns[d];
  if (openDropdown.classList.contains('show')) {
    openDropdown.classList.remove('show');
   }
  }
 }
}

   ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    background-color: #333;
    }

    li {
    float: left;
    }

    li a, .dropbtn {
    display: inline-block;
    color: white;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    }

    li a:hover, .dropdown:hover .dropbtn {
    background-color: red;
    }

    li.dropdown {
       display: inline-block;
    }

    .dropdown-content {
    display: none;
    position: absolute;
    background-color: #f9f9f9;
    min-width: 160px;
    box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
    }

    .dropdown-content a {
    color: black;
    padding: 12px 16px;
    text-decoration: none;
    display: block;
    text-align: left;
    }

    .dropdown-content a:hover {background-color: #f1f1f1}

    .show {display:block;}

    <nav>
	  <ul>
		<li><a href='front.html'>Home</a></li>
		<li><a href='intro.html'>Intro</a></li>
		<li><a href='how.html'>How it Works</a></li>
		<li><a href='best.html'>Using it</a></li>
		<li class ="dropdown">
			<a href="javascript:void(0)" class="dropbtn" 
			onclick="myFunction()">Examples</a>
				<ul class="dropdown-content" id="myDropdown">
				<div class="dropdown-content" id="myDropdown">
					<li><a href='saga.html'>SAGA</a></li>
					<li><a href='portfolio.html'>Portfolio Optimization</a></li>
					<li><a href='circuits.html'>Evolved Circuits</a></li>
				</div>
				</ul>
		</li>
		<li><a href='about.html'>References</a></li>
	</ul>
   </nav>

Answer 1

除了您正在寻找的所需样式之外，似乎您在<div class="dropdown-content" id="myDropdown">中有一个不需要的包装ul，使列表保持display: none。删除它很有效。

＆＃13;

＆＃13;

function myFunction() {
document.getElementById("myDropdown").classList.toggle("show");
 }
 window.onclick = function(e) {
if (!e.target.matches('.dropbtn')) {

var dropdowns = document.getElementsByClassName("dropdown-content");
for (var d = 0; d < dropdowns.length; d++) {
  var openDropdown = dropdowns[d];
  if (openDropdown.classList.contains('show')) {
    openDropdown.classList.remove('show');
   }
  }
 }
}

＆＃13;

ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    background-color: #333;
    }

    li {
    float: left;
    }

    li a, .dropbtn {
    display: inline-block;
    color: white;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    }

    li a:hover, .dropdown:hover .dropbtn {
    background-color: red;
    }

    li.dropdown {
       display: inline-block;
    }

    .dropdown-content {
    display: none;
    position: absolute;
    background-color: #f9f9f9;
    min-width: 160px;
    box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
    }

    .dropdown-content a {
    color: black;
    padding: 12px 16px;
    text-decoration: none;
    display: block;
    text-align: left;
    }

    .dropdown-content a:hover {background-color: #f1f1f1}

    .show {display:block;}

＆＃13;

<nav>
	  <ul>
		<li><a href='front.html'>Home</a></li>
		<li><a href='intro.html'>Intro</a></li>
		<li><a href='how.html'>How it Works</a></li>
		<li><a href='best.html'>Using it</a></li>
		<li class ="dropdown">
			<a href="javascript:void(0)" class="dropbtn" 
			onclick="myFunction()">Examples</a>
				<ul class="dropdown-content" id="myDropdown">
					<li><a href='saga.html'>SAGA</a></li>
					<li><a href='portfolio.html'>Portfolio Optimization</a></li>
					<li><a href='circuits.html'>Evolved Circuits</a></li>
				</ul>
		</li>
		<li><a href='about.html'>References</a></li>
	</ul>
   </nav>

＆＃13;

＆＃13;

＆＃13;

Answer 2

我刚刚删除了ul标签中的div并覆盖了下拉列表的li标签样式（删除浮动：左边的那些li标签）

function myFunction() {
document.getElementById("myDropdown").classList.toggle("show");
 }
 window.onclick = function(e) {
if (!e.target.matches('.dropbtn')) {

var dropdowns = document.getElementsByClassName("dropdown-content");
for (var d = 0; d < dropdowns.length; d++) {
  var openDropdown = dropdowns[d];
  if (openDropdown.classList.contains('show')) {
    openDropdown.classList.remove('show');
   }
  }
 }
}

   ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    background-color: #333;
    }

    li {
    float: left;
    }
    .dropdown-content li {
     float: none !important; 
    }

    li a, .dropbtn {
    display: inline-block;
    color: white;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    }

    li a:hover, .dropdown:hover .dropbtn {
    background-color: red;
    }

    li.dropdown {
       display: inline-block;
    }

    .dropdown-content {
    display: none;
    position: absolute;
    background-color: #f9f9f9;
    min-width: 160px;
    box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
    }

    .dropdown-content a {
    color: black;
    padding: 12px 16px;
    text-decoration: none;
    display: block;
    text-align: left;
    }

    .dropdown-content a:hover {background-color: #f1f1f1}

    .show {display:block;}

    <nav>
	  <ul>
		<li><a href='front.html'>Home</a></li>
		<li><a href='intro.html'>Intro</a></li>
		<li><a href='how.html'>How it Works</a></li>
		<li><a href='best.html'>Using it</a></li>
		<li class ="dropdown">
			<a href="javascript:void(0)" class="dropbtn" 
			onclick="myFunction()">Examples</a>
				<ul class="dropdown-content" id="myDropdown">
					<li><a href='saga.html'>SAGA</a></li>
					<li><a href='portfolio.html'>Portfolio Optimization</a></li>
					<li><a href='circuits.html'>Evolved Circuits</a></li>
				</div>
				</ul>
		</li>
		<li><a href='about.html'>References</a></li>
	</ul>
   </nav>

Answer 3

function myFunction() {
  document.getElementById("myDropdown").classList.toggle("show");
}
window.onclick = function(e) {
  if (!e.target.matches('.dropbtn')) {

    var dropdowns = document.getElementsByClassName("dropdown-content");
    for (var d = 0; d < dropdowns.length; d++) {
      var openDropdown = dropdowns[d];
      if (openDropdown.classList.contains('show')) {
        openDropdown.classList.remove('show');
      }
    }
  }
}

ul {
list-style-type: none;
margin: 0;
padding: 0;
overflow: hidden;
background-color: #333;
}

li {
float: left;
}

li a, .dropbtn {
display: inline-block;
color: white;
text-align: center;
padding: 14px 16px;
text-decoration: none;
}

li a:hover, .dropdown:hover .dropbtn {
background-color: red;
}

li.dropdown {
   display: inline-block;
}

.dropdown-content {
display: none;
position: fixed;
background-color: #f9f9f9;
min-width: 160px;
box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
}
.dropdown-content li{
	float: none;
}

.dropdown-content a {
color: black;
padding: 12px 16px;
text-decoration: none;
display: block;
text-align: left;
}

.dropdown-content a:hover {background-color: #f1f1f1}

.show {
	display:block;
   	}

<nav>
  <ul>
    <li><a href='front.html'>Home</a></li>
    <li><a href='intro.html'>Intro</a></li>
    <li><a href='how.html'>How it Works</a></li>
    <li><a href='best.html'>Using it</a></li>
    <li class ="dropdown">
      <a href="javascript:void(0)" class="dropbtn" 
         onclick="myFunction()">Examples</a>
      <ul class="dropdown-content" id="myDropdown">
        <li><a href='saga.html'>SAGA</a></li>
        <li><a href='portfolio.html'>Portfolio Optimization</a></li>
        <li><a href='circuits.html'>Evolved Circuits</a></li>
      </ul>
    </li>
    <li><a href='about.html'>References</a></li>
  </ul>
</nav>

您应该将 position: fixed; 添加到.dropdown内容类，.dropdown-content li 应该有 float: none;以获得下拉原始效果。