本文旨在解决在使用 W3Schools 提供的响应式导航栏代码时，遇到的下拉菜单点击后不显示或消失的问题。我们将详细介绍问题的可能原因，并提供清晰的步骤和代码示例，帮助你修复导航栏的下拉菜单功能，确保在各种设备上都能正常工作。
当响应式导航栏的下拉菜单点击后不显示，或者在滚动页面后消失时，通常是由于以下几个原因造成的：
针对以上问题，我们可以采取以下步骤来解决：
1. 引入 JavaScript 代码
确保 HTML 文件中包含以下 JavaScript 代码，并将其放置在 <body> 标签的末尾或 <head> 标签中：
<script>
function myFunction() {
var x = document.getElementById("myTopnav");
if (x.className === "topnav") {
x.className += " responsive";
} else {
x.className = "topnav";
}
}
</script>这段代码的作用是：当点击 toggle 图标时，会给导航栏的 topnav 类添加或移除 responsive 类，从而控制导航栏在小屏幕上的显示方式。
2. 引入 Font Awesome 图标库
在 <head> 标签中添加以下代码，引入 Font Awesome 图标库：
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
这将确保 toggle 图标（三条横线）能够正确显示。
3. 检查 CSS 样式
仔细检查 CSS 样式，确保没有覆盖或冲突的样式导致下拉菜单无法正确显示。特别是以下几个方面：
4. 确保页面内容足够
为了测试滚动后下拉菜单是否正常工作，确保页面内容足够长，以至于出现滚动条。可以在 HTML 文件中添加一些额外的文本或元素，例如：
<p> Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum. </p> <p> ... (重复以上段落多次) ... </p>
5. 完整代码示例
以下是一个完整的代码示例，包含了 HTML、CSS 和 JavaScript 代码：
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
<style>
/* Add a black background color to the top navigation */
.topnav {
background-color: #333;
overflow: hidden;
}
/* Style the links inside the navigation bar */
.topnav a {
float: left;
display: block;
color: #f2f2f2;
text-align: center;
padding: 14px 16px;
text-decoration: none;
font-size: 17px;
}
/* Add an active class to highlight the current page */
.active {
background-color: #04AA6D;
color: white;
}
/* Hide the link that should open and close the topnav on small screens */
.topnav .icon {
display: none;
}
/* Dropdown container - needed to position the dropdown content */
.dropdown {
float: left;
overflow: hidden;
}
/* Style the dropdown button to fit inside the topnav */
.dropdown .dropbtn {
font-size: 17px;
border: none;
outline: none;
color: white;
padding: 14px 16px;
background-color: inherit;
font-family: inherit;
margin: 0;
}
/* Style the dropdown content (hidden by default) */
.dropdown-content {
display: none;
position: absolute;
background-color: #f9f9f9;
min-width: 160px;
box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
z-index: 1;
}
/* Style the links inside the dropdown */
.dropdown-content a {
float: none;
color: black;
padding: 12px 16px;
text-decoration: none;
display: block;
text-align: left;
}
/* Add a dark background on topnav links and the dropdown button on hover */
.topnav a:hover, .dropdown:hover .dropbtn {
background-color: #555;
color: white;
}
/* Add a grey background to dropdown links on hover */
.dropdown-content a:hover {
background-color: #ddd;
color: black;
}
/* Show the dropdown menu when the user moves the mouse over the dropdown button */
.dropdown:hover .dropdown-content {
display: block;
}
/* When the screen is less than 600 pixels wide, hide all links, except for the first one ("Home"). Show the link that contains should open and close the topnav (.icon) */
@media screen and (max-width: 600px) {
.topnav a:not(:first-child), .dropdown .dropbtn {
display: none;
}
.topnav a.icon {
float: right;
display: block;
}
}
/* The "responsive" class is added to the topnav with JavaScript when the user clicks on the icon. This class makes the topnav look good on small screens (display the links vertically instead of horizontally) */
@media screen and (max-width: 600px) {
.topnav.responsive {position: relative;}
.topnav.responsive a.icon {
position: absolute;
right: 0;
top: 0;
}
.topnav.responsive a {
float: none;
display: block;
text-align: left;
}
.topnav.responsive .dropdown {float: none;}
.topnav.responsive .dropdown-content {position: relative;}
.topnav.responsive .dropdown .dropbtn {
display: block;
width: 100%;
text-align: left;
}
}
</style>
</head>
<body>
<div class="topnav" id="myTopnav">
<a href="#home" class="active">Home</a>
<a href="#news">News</a>
<a href="#contact">Contact</a>
<div class="dropdown">
<button class="dropbtn">Dropdown
<i class="fa fa-caret-down"></i>
</button>
<div class="dropdown-content">
<a href="#">Link 1</a>
<a href="#">Link 2</a>
<a href="#">Link 3</a>
</div>
</div>
<a href="#about">About</a>
<a href="javascript:void(0);" class="icon" onclick="myFunction()">
<i class="fa fa-bars"></i>
</a>
</div>
<p>
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
</p>
<p>
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
</p>
<p>
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
</p>
<p>
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
</p>
<p>
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
</p>
<p>
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
</p>
<script>
function myFunction() {
var x = document.getElementById("myTopnav");
if (x.className === "topnav") {
x.className += " responsive";
} else {
x.className = "topnav";
}
}
</script>
</body>
</html>总结
通过以上步骤，你应该能够解决响应式导航栏下拉菜单点击失效的问题。 关键在于确保 JavaScript 代码正确引入，Font Awesome 图标库可用，以及 CSS 样式没有冲突。 仔细检查每个步骤，并根据你的具体情况进行调整，最终实现一个功能完善的响应式导航栏。
以上就是解决响应式导航栏下拉菜单点击失效问题的详细内容，更多请关注php中文网其它相关文章！
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