传统的HTML页面中连动下拉框采用了两种方法：1）直接将下拉框中的内容hardcode于html的javascript中，调用javascript函数循环写入下拉框中。这种方法不适用于下拉框内容经常改变的情况。因为数据源和javascript程序写死在同一页面。<html><head><title>List</title><meta http-equiv="Content-Type" content="text/html; charset=gb2312"><script LANGUAGE="javascript"><!--var onecount;onecount=0;
subcat = new Array();subcat[0] = new Array("徐汇区","01","001");subcat[1] = new Array("嘉定区","01","002");subcat[2] = new Array("黄浦区","01","003");subcat[3] = new Array("南昌市","02","004");subcat[4] = new Array("九江市","02","005");subcat[5] = new Array("上饶市","02","006");
onecount=6;
function changelocation(locationid){document.myform.smalllocation.length = 0;
var locationid=locationid;var i;document.myform.smalllocation.options[0] = new Option('====所有地区====','');for (i=0;i <onecount; i++){if (subcat[i][1] == locationid){document.myform.smalllocation.options[document.myform.smalllocation.length]= new Option(subcat[i][0], subcat[i][2]);}}
}
//--></script></head><body><form name="myform" method="post"><select name="biglocation"onChange="changelocation(document.myform.biglocation.options[document.myform.biglocation.selectedIndex].value)"><option value="01" selected>上海</option><option value="02">江西</option></select><select name="smalllocation"><option selected value="">==所有地区==</option></select></form><script LANGUAGE="javascript"><!--changelocation(document.myform.biglocation.options[document.myform.biglocation.selectedIndex].value);//--></script></body></html>
2）javascript 直接读取数据库，取数据库中的记录写入javascript中，然后和第一种方法一样，调用javascript函数循环写入下拉框中。此方法将数据源与javascript分开，但,公开数据库的连接，从安全角度说，没有多少实用价值。
我的方法是将下拉框中的数据放在XML文件中，用javascript读XML文件，取得下拉框中的内容。
HTML 文件如下：<!-- myfile.html -->
<html><head><script language="JavaScript" for="window" event="onload">var xmlDoc = new ActiveXObject("Microsoft.XMLDOM");var i=0;var j=0;var subclass_name="";loadXML();function loadXML(){xmlDoc.async="false";xmlDoc.load("account.xml");xmlObj=xmlDoc.documentElement;nodes = xmlDoc.documentElement.childNodes;document.frm.mainclass.options.length = 0;document.frm.subclass.options.length = 0;
for (i=0;i<xmlObj.childNodes.length;i++){labels=xmlObj.childNodes(i).getAttribute("display_name");values=xmlObj.childNodes(i).text;document.frm.mainclass.add(document.createElement("OPTION"));document.frm.mainclass.options[i].text=labels;document.frm.mainclass.options[i].value=values;
}
}
</script>
<script language="JavaScript" >var xmlDoc = new ActiveXObject("Microsoft.XMLDOM");var i=0;var j=0;
function deleteOption() {
}
function setsubclass(main){var is_selected="N";if (document.frm.subclass.options.length!=0) {for (i=0;i<=document.frm.subclass.options.length;i++)document.frm.subclass.options[i]=null ;}//重复才有效if (document.frm.subclass.options.length!=0) {for (i=0;i<=document.frm.subclass.options.length;i++){document.frm.subclass.options[i]=null ;document.frm.subclass.options.remove(i);}}
for (i=0;i<xmlObj.childNodes.length;i++){
var values="";var lables="";
if (is_selected=="Y") return;labels=xmlObj.childNodes(i).getAttribute("display_name");values=xmlObj.childNodes(i).text;//alert(labels+ " | "+main);if (labels==main){
is_selected="Y";
for (j=0;j<xmlObj.childNodes(i).childNodes.length;j++){//subclass_name="document.frm.subclass";labels=xmlObj.childNodes(i).childNodes(j).getAttribute("display_name");values=xmlObj.childNodes(i).childNodes(j).text;//alert(values);document.frm.subclass.add(document.createElement("OPTION"));document.frm.subclass.options[j].text=labels;document.frm.subclass.options[j].value=values;
}
}
}}</script>
<title>在HTML中调用XML数据</title></head><body bgcolor="#FFFFFF"><FORM NAME="frm">类型<SELECT NAME="mainclass" OnChange='setsubclass(this[selectedIndex].text)'></SELECT><option selected value=""
></option>子类<SELECT NAME="subclass"></SELECT></form></body></html>
account.xml 如下：
<?xml version="1.0" encoding="GB2312"?><item><class display_name="未选定"><subclass display_name="">Not Available</subclass></class><class display_name="95788主叫卡"><subclass display_name="1152069589-1152069638">dangdang1</subclass><subclass display_name="1152081031-1152081080">dangdang2</subclass><subclass display_name="1152547201-1105254750">dangdang3</subclass><subclass display_name="1152548401-1152548700">dangdang4</subclass><subclass display_name="1152548701-1152549000">dangdang5</subclass><subclass display_name="1156000001-1156010000">dangdang6</subclass></class><class display_name="网上注册"><subclass display_name="1152000001-1152001000">zhuce_user1</subclass><subclass display_name="1151001000-1151005000">zhuce_user2</subclass></class><class display_name="通讯"><subclass display_name="1156030001-1156080000">tongxun</subclass></class></item>
此方法将数据源与javascript程序分开，适合经常变化的数据源。xmlDoc.load中可以直接调用URL参数,读取远程XML，实现松耦合。以上应用在IE6.0中通过。不足之处是在去除下拉框列表内容时需要重复执行删除操作，否则会有明显的bug.希望有读者能给指正。
