jquery 和css 实现下拉菜单

第1步：HTML文档

首先为你的导航创建一个无序列表，然后简单的写一下另外一个无序列表作为导航子菜单

<ul class="topnav">
    <li><a href="#">Home</a></li>
    <li>
        <a href="#">Tutorials</a>
        <ul class="subnav">
            <li><a href="#">Sub Nav Link</a></li>
            <li><a href="#">Sub Nav Link</a></li>
        </ul>
    </li>
    <li>
        <a href="#">Resources</a>
        <ul class="subnav">
            <li><a href="#">Sub Nav Link</a></li>
            <li><a href="#">Sub Nav Link</a></li>
        </ul>
    </li>
    <li><a href="#">About Us</a></li>
    <li><a href="#">Advertise</a></li>
    <li><a href="#">Submit</a></li>
    <li><a href="#">Contact Us</a></li>
</ul>

<ul class="topnav">
    <li><a href="#">Home</a></li>
    <li>
        <a href="#">Tutorials</a>
        <ul class="subnav">
            <li><a href="#">Sub Nav Link</a></li>
            <li><a href="#">Sub Nav Link</a></li>
        </ul>
    </li>
    <li>
        <a href="#">Resources</a>
        <ul class="subnav">
            <li><a href="#">Sub Nav Link</a></li>
            <li><a href="#">Sub Nav Link</a></li>
        </ul>
    </li>
    <li><a href="#">About Us</a></li>
    <li><a href="#">Advertise</a></li>
    <li><a href="#">Submit</a></li>
    <li><a href="#">Contact Us</a></li>
</ul>

第2步：CSS

然后定义导航样式

ul.topnav {
    list-style: none;
    padding: 0 20px;
    margin: 0;
    float: left;
    width: 920px;
    background: #222;
    font-size: 1.2em;
    background: url(topnav_bg.gif) repeat-x;
}
ul.topnav li {
    float: left;
    margin: 0;
    padding: 0 15px 0 0;
    position: relative; /*--Declare X and Y axis base for sub navigation--*/
}
ul.topnav li a{
    padding: 10px 5px;
    color: #fff;
    display: block;
    text-decoration: none;
    float: left;
}
ul.topnav li a:hover{
    background: url(topnav_hover.gif) no-repeat center top;
}
ul.topnav li span { /*--Drop down trigger styles--*/
    width: 17px;
    height: 35px;
    float: left;
    background: url(subnav_btn.gif) no-repeat center top;
}
ul.topnav li span.subhover
 {background-position: center bottombottom; cursor: pointer;}
/*--Hover effect for trigger--*/
ul.topnav li ul.subnav {
    list-style: none;
    position: absolute;
 /*--Important - Keeps subnav from affecting main navigation flow--*/
    left: 0; top: 35px;
    background: #333;
    margin: 0; padding: 0;
    display: none;
    float: left;
    width: 170px;
    border: 1px solid #111;
}
ul.topnav li ul.subnav li{
    margin: 0; padding: 0;
    border-top: 1px solid #252525; /*--Create bevel effect--*/
    border-bottom: 1px solid #444; /*--Create bevel effect--*/
    clear: both;
    width: 170px;
}
html ul.topnav li ul.subnav li a {
    float: left;
    width: 145px;
    background: #333 url(dropdown_linkbg.gif) no-repeat 10px center;
    padding-left: 20px;
}
html ul.topnav li ul.subnav li a:hover { /*--Hover effect for subnav links--*/
    background: #222 url(dropdown_linkbg.gif) no-repeat 10px center;
}

ul.topnav {
	list-style: none;
	padding: 0 20px;
	margin: 0;
	float: left;
	width: 920px;
	background: #222;
	font-size: 1.2em;
	background: url(topnav_bg.gif) repeat-x;
}
ul.topnav li {
	float: left;
	margin: 0;
	padding: 0 15px 0 0;
	position: relative; /*--Declare X and Y axis base for sub navigation--*/
}
ul.topnav li a{
	padding: 10px 5px;
	color: #fff;
	display: block;
	text-decoration: none;
	float: left;
}
ul.topnav li a:hover{
	background: url(topnav_hover.gif) no-repeat center top;
}
ul.topnav li span { /*--Drop down trigger styles--*/
	width: 17px;
	height: 35px;
	float: left;
	background: url(subnav_btn.gif) no-repeat center top;
}
ul.topnav li span.subhover {background-position: center bottom; cursor: pointer;}

 /*--Hover effect for trigger--*/
ul.topnav li ul.subnav {
	list-style: none;
	position: absolute; 

/*--Important - Keeps subnav from affecting main navigation flow--*/
	left: 0; top: 35px;
	background: #333;
	margin: 0; padding: 0;
	display: none;
	float: left;
	width: 170px;
	border: 1px solid #111;
}
ul.topnav li ul.subnav li{
	margin: 0; padding: 0;
	border-top: 1px solid #252525; /*--Create bevel effect--*/
	border-bottom: 1px solid #444; /*--Create bevel effect--*/
	clear: both;
	width: 170px;
}
html ul.topnav li ul.subnav li a {
	float: left;
	width: 145px;
	background: #333 url(dropdown_linkbg.gif) no-repeat 10px center;
	padding-left: 20px;
}
html ul.topnav li ul.subnav li a:hover { /*--Hover effect for subnav links--*/
	background: #222 url(dropdown_linkbg.gif) no-repeat 10px center;
}

第3步：jQuery

下面的脚本包含的内容解释了JQuery将要执行的的动作，你是jQuery新手？看这里.

 

$(document).ready(function(){

    $("ul.subnav").parent().append("<span></span>"); //Only shows drop down trigger when js is enabled

 (Adds empty span tag after ul.subnav*)   

    $("ul.topnav li span").click(function() { //When trigger is clicked...

   //Following events are applied to the subnav itself (moving subnav up and down)
 $(this).parent().find("ul.subnav").slideDown('fast').show();
//Drop down the subnav on click

        $(this).parent().hover(function() {
        }, function(){
            $(this).parent().find("ul.subnav").slideUp('slow'); //When the mouse hovers out of the subnav, move it back up
        });

        //Following events are applied to the trigger (Hover events for the trigger)
        }).hover(function() {
            $(this).addClass("subhover"); //On hover over, add class "subhover"
        }, function(){  //On Hover Out
            $(this).removeClass("subhover"); //On hover out, remove class "subhover"
    });

});

$(document).ready(function(){

	$("ul.subnav").parent().append("<span></span>"); 

//Only shows drop down trigger when js is enabled (Adds empty span tag after ul.subnav*)

	$("ul.topnav li span").click(function() { //When trigger is clicked...

//Following events are applied to the subnav itself (moving subnav up and down)
	$(this).parent().find("ul.subnav").slideDown('fast').show(); 

//Drop down the subnav on click

		$(this).parent().hover(function() {
		}, function(){
		$(this).parent().find("ul.subnav").slideUp('slow');

 //When the mouse hovers out of the subnav, move it back up
		});

		//Following events are applied to the trigger (Hover events for the trigger)
		}).hover(function() {
		$(this).addClass("subhover"); //On hover over, add class "subhover"
		}, function(){	//On Hover Out
	$(this).removeClass("subhover"); //On hover out, remove class "subhover"
	});

});

下拉菜单只是在支持javascript的的情况下才会显示并触发。