DedeCMS下拉菜单生成：轻松实现导航栏的多功能设计

dedecms做下拉菜单：

将下面这段代码贴到templets\default\footer.htm文件里

<!-- //二级子类下拉菜单，考虑SEO原因放置于底部 -->
    <script type='text/javascript' src='{dede:global.cfg_cmsurl/}/images/js/dropdown.js'></script>
    {dede:channelartlist typeid='top' cacheid='channelsonlist'}
    <ul id="dropmenu{dede:field.typeid/}" class="dropMenu">
        {dede:channel type='son' noself='yes'}
        <li><a href="[field:typelink/]">[field:typename/]</a></li>
        {/dede:channel}
    </ul>
    {/dede:channelartlist}
    <script type="text/javascript">cssdropdown.startchrome("navMenu")</script>

以上代码可以看出，二级子类下拉菜单是由dropdown.js控制的，我们来看dropdown.js文件：

由以上的cssdropdown.startchrome("navMenu")，可以看出我们调用的是 startchrome:function()

var cssdropdown={
disappeardelay: 250, 
disablemenuclick: false, 
enableswipe: 1, 
enableiframeshim: 1, 
dropmenuobj: null, ie: document.all, firefox: document.getElementById&&!document.all, swipetimer: undefined, bottomclip:0,
 
getposOffset:function(what, offsettype){
var totaloffset=(offsettype=="left")? what.offsetLeft : what.offsetTop;
var parentEl=what.offsetParent;
while (parentEl!=null){
totaloffset=(offsettype=="left")? totaloffset+parentEl.offsetLeft : totaloffset+parentEl.offsetTop;
parentEl=parentEl.offsetParent;
}
return totaloffset;
},
 
swipeeffect:function(){
if (this.bottomclip<parseInt(this.dropmenuobj.offsetHeight)){
this.bottomclip+=10+(this.bottomclip/10) 
this.dropmenuobj.style.clip="rect(0 auto "+this.bottomclip+"px 0)"
}
else
return
this.swipetimer=setTimeout("cssdropdown.swipeeffect()", 10)
},
 
showhide:function(obj, e){
if (this.ie || this.firefox)
this.dropmenuobj.style.left=this.dropmenuobj.style.top="-500px"
if (e.type=="click" && obj.visibility==hidden || e.type=="mouseover"){
if (this.enableswipe==1){
if (typeof this.swipetimer!="undefined")
clearTimeout(this.swipetimer)
obj.clip="rect(0 auto 0 0)" 
this.bottomclip=0
this.swipeeffect()
}
obj.visibility="visible"
}
else if (e.type=="click")
obj.visibility="hidden"
},
 
iecompattest:function(){
return (document.compatMode && document.compatMode!="BackCompat")? document.documentElement : document.body
},
 
clearbrowseredge:function(obj, whichedge){
var edgeoffset=0
if (whichedge=="rightedge"){
var windowedge=this.ie && !window.opera? this.iecompattest().scrollLeft+this.iecompattest().clientWidth-15 : window.pageXOffset+window.innerWidth-15
this.dropmenuobj.contentmeasure=this.dropmenuobj.offsetWidth
if (windowedge-this.dropmenuobj.x < this.dropmenuobj.contentmeasure)  
edgeoffset=this.dropmenuobj.contentmeasure-obj.offsetWidth
}
else{
var topedge=this.ie && !window.opera? this.iecompattest().scrollTop : window.pageYOffset
var windowedge=this.ie && !window.opera? this.iecompattest().scrollTop+this.iecompattest().clientHeight-15 : window.pageYOffset+window.innerHeight-18
this.dropmenuobj.contentmeasure=this.dropmenuobj.offsetHeight
if (windowedge-this.dropmenuobj.y < this.dropmenuobj.contentmeasure){ 
edgeoffset=this.dropmenuobj.contentmeasure+obj.offsetHeight
if ((this.dropmenuobj.y-topedge)<this.dropmenuobj.contentmeasure) 
edgeoffset=this.dropmenuobj.y+obj.offsetHeight-topedge
}
}
return edgeoffset
},
 
dropit:function(obj, e, dropmenuID){
if (this.dropmenuobj!=null) 
	this.dropmenuobj.style.visibility="hidden" 
this.clearhidemenu()
if (this.ie||this.firefox){
obj.οnmοuseοut=function(){cssdropdown.delayhidemenu()}
obj.οnclick=function(){return !cssdropdown.disablemenuclick} 
this.dropmenuobj=document.getElementById(dropmenuID)
if(!this.dropmenuobj) return;
this.dropmenuobj.οnmοuseοver=function(){cssdropdown.clearhidemenu()}
this.dropmenuobj.οnmοuseοut=function(e){cssdropdown.dynamichide(e)}
this.dropmenuobj.οnclick=function(){cssdropdown.delayhidemenu()}
this.showhide(this.dropmenuobj.style, e)
this.dropmenuobj.x=this.getposOffset(obj, "left")
this.dropmenuobj.y=this.getposOffset(obj, "top")
this.dropmenuobj.style.left=this.dropmenuobj.x-this.clearbrowseredge(obj, "rightedge")+"px"
this.dropmenuobj.style.top=this.dropmenuobj.y-this.clearbrowseredge(obj, "bottomedge")+obj.offsetHeight+1+"px"
this.positionshim() 
}
},
 
positionshim:function(){ 
if (this.enableiframeshim && typeof this.shimobject!="undefined"){
if (this.dropmenuobj.style.visibility=="visible"){
this.shimobject.style.width=this.dropmenuobj.offsetWidth+"px"
this.shimobject.style.height=this.dropmenuobj.offsetHeight+"px"
this.shimobject.style.left=this.dropmenuobj.style.left
this.shimobject.style.top=this.dropmenuobj.style.top
}
this.shimobject.style.display=(this.dropmenuobj.style.visibility=="visible")? "block" : "none"
}
},
 
hideshim:function(){
if (this.enableiframeshim && typeof this.shimobject!="undefined")
this.shimobject.style.display='none'
},
 
contains_firefox:function(a, b) {
while (b.parentNode)
if ((b = b.parentNode) == a)
return true;
return false;
},
 
dynamichide:function(e){
var evtobj=window.event? window.event : e
if (this.ie&&!this.dropmenuobj.contains(evtobj.toElement))
this.delayhidemenu()
else if (this.firefox&&e.currentTarget!= evtobj.relatedTarget&& !this.contains_firefox(evtobj.currentTarget, evtobj.relatedTarget))
this.delayhidemenu()
},
 
delayhidemenu:function(){
this.delayhide=setTimeout("cssdropdown.dropmenuobj.style.visibility='hidden'; cssdropdown.hideshim()",this.disappeardelay) 
},
 
clearhidemenu:function(){
if (this.delayhide!="undefined")
clearTimeout(this.delayhide)
},
 
startchrome:function(){
for (var ids=0; ids<arguments.length; ids++){
var menuitems=document.getElementById(arguments[ids]).getElementsByTagName("a")
for (var i=0; i<menuitems.length; i++){
if (menuitems[i].getAttribute("rel")){
var relvalue=menuitems[i].getAttribute("rel")
menuitems[i].οnmοuseοver=function(e){
var event=typeof e!="undefined"? e : window.event
cssdropdown.dropit(this,event,this.getAttribute("rel"))
}
}
}
}
if (window.createPopup && !window.XmlHttpRequest){ 
document.write('<IFRAME id="iframeshim"  src=""  frameBorder="0" scrolling="no"></IFRAME>')
this.shimobject=document.getElementById("iframeshim") 
}
}
}

由上可以看出，var cssdropdown变量中有多个函数：

getposOffset:function(what, offsettype)
swipeeffect:function()
showhide:function(obj, e) 
iecompattest:function()
clearbrowseredge:function(obj, whichedge)
dropit:function(obj, e, dropmenuID)
positionshim:function()
hideshim:function()
dynamichide:function(e)
delayhidemenu:function()
clearhidemenu:function()
startchrome:function()

更新一下！会发现导航栏已经出现下拉菜单了，只是背景是透明的，原因是没有背景图片。

然后我们可以对此下拉菜单添加背景图片和设置css样式。

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