请高手看看以下代码错在什么地方了?

[chengcharect]

	<script type="text/javascript" language="javascript">
	var browse="";
	
	function enableChoic(id){
	    document.getElementById(id).disabled = false;
	}

	//创建ajax
	function GetXmlHttpObject()	{
		var xmlHttp=null;
		try {
			// Firefox, Opera 8.0+, Safari
			xmlHttp=new XMLHttpRequest();
		}catch (e) {
		 	//Internet Explorer
			try {
		  		xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
		  	} catch (e) {
		  		xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
		  	}
		}
		return xmlHttp;
	}
		
	function changeSubject(_slt){
		xmlHttp=GetXmlHttpObject();
		if (xmlHttp==null){
		 	alert ("浏览器无法返回ajax对象!");
		 	return;
		}

		var url="user_xml.php?users=" + _slt.value;
		alert(url);
		xmlHttp.onreadystatechange=stateChanged;
		xmlHttp.open("GET",url,true);
		xmlHttp.send(null);
	}

	//用于解决IE读取xmDoc与FF不同
	function loadXMLString(txt){
		try{//Internet Explorer
		  	xmlDoc=new ActiveXObject("Microsoft.XMLDOM");
		  	xmlDoc.async="false";
		  	xmlDoc.loadXML(txt);
		  	return(xmlDoc);  
		}catch(e){
			try{//Firefox, Mozilla, Opera, etc.
			    parser=new DOMParser();
			    xmlDoc=parser.parseFromString(txt,"text/xml");
			    return(xmlDoc);
			}catch(e) {
				 alert(e.message)
			}
		}
		return(null);
	}
	
	function stateChanged(data){
		var user_science = document.getElementsByName("user_science")[0];
		if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete"){
			if (xmlHttp.status == 200) {
				var xmlDoc = loadXMLString(xmlHttp.responseText);
				$("#s2>option:gt(0)").remove();//清空除第一项除外的option
//				//解析XML
				var root=xmlDoc.getElementsByTagName('row');
				for (var i=0; i<root.length; i++){
					var value = root[i].getElementsByTagName("value")[0].childNodes[0].nodeValue;
					var text = root[i].getElementsByTagName("text")[0].childNodes[0].nodeValue;
					$("#s2").get(0).options.add(new Option(text,value));
				} 				
			}
		}
	}
</script>
    <form action="user_search_sql.php" method="post">
	<ul>
        <li><!--<input type="checkbox" id="chk_1" name="s_grade" checked="true" onclick="enableChoic('s1')">年 级-->
        <select name="user_grade" onchange="changeSubject(this);">
		<option value="">--选择入学年份--</option>
        <?php
				$login_sql = "select * from klm_users group by user_grade";
				$result = $db->query ( $login_sql );
				while ( $row = $db->fetch_array ( $result ) ) {
			?>
	    	<option value="<?php echo $row ['user_grade']; ?>"
			<?php
				if ($row ['user_grade'] == $typeid) {
					echo "selected";
				}
			?>
			><?php echo $row ['user_grade']; ?></option>
			<?php
				}
			?>
        </select></li>
        <li> <!--<input type="checkbox" id="chk_2" name="s_science" onclick="enableChoic('s2')">专 业-->
        <select ID="s2" name="user_science" SIZE="1">
        <option value="">--选择专业--</option>
        </select></li>
        <li> <!--<input type="checkbox" id="chk_3" name="s_class" onclick="enableChoic('s3')">班 级-->
        <select ID="s3" name="user_class" SIZE="1">
        <option value="">--选择班级--</option>
        </select></li>
        <li><input type="submit" class="btn_2" value="点击查询"></li>
	</ul>
</form>

user_xml.php

<?php
include_once ('admin_global.php');
header ( 'Content-Type:text/xml; charset=gbk' );
if ($_GET ["users"]) {
	$login_sql = "select * from klm_users where user_grade=" . $_GET ["users"];
	echo $login_sql;
	$result = $db->query($login_sql);
	$xml = "<?xml version=\"1.0\"?><rows>";
	while ( $row = $db->fetch_array ( $result ) ) {
		$xml .= "<row><value>" . $row ["user_grade"] . "</value><text>" . $row ["user_science"] . "</text></row>";
	}
	$xml .= "</rows>";
	echo $xml;
}

exit ();
?>

[kyzy_yy_pm]

什么错误说出来

[chengcharect]

XML的内容取不出来.就是二级和三级菜单取不到.求高手解答.跪谢

[xuzuning]

请说明你遇到了什么问题！

[kyzy_yy_pm]

user_xml.php中将while换成

while ( $row = $db->fetch_array ( $result ) ) {
echo '<pre>';print_r($row);echo '<br>';
}
看看数据

[chengcharect]

单独访问user_xml.php的时候页面报错.
XML 文档必须有一个顶层元素。处理资源 'http://localhost:81/klmexam/admin/user_xml.php' 时出错。

[kyzy_yy_pm]

$header = "<root>"
$end = "</root>";
while ( $row = $db->fetch_array ( $result ) ) {
$xml .= "<row><value>" . $row ["user_grade"] . "</value><text>" . $row ["user_science"] . "</text></row>";
}

$xml = $header.$xml.$end;

[kyzy_yy_pm]

没有最终父节点

[chengcharect]

按照楼上的做法.XML还是报错
XML 文档必须有一个顶层元素。处理资源 'http://localhost:81/klmexam/admin/user_xml.php' 时出错。

[chengcharect]

T.T没人高手来帮帮忙么?

[kyzy_yy_pm]

echo $xml = $header.$xml.$end;//看看

[chengcharect]

[Quote=引用 10 楼 kyzy_yy_pm 的回复:]
echo $xml = $header.$xml.$end;//看看
[/Quote]
Notice: /klmexam/admin/user_xml.php line 20 - Undefined variable: xml

[kyzy_yy_pm]

$xml = "<?xml version=\"1.0\"?><rows>";
while ( $row = $db->fetch_array ( $result ) ) {
$xml .= "<row><value>" . $row ["user_grade"] . "</value><text>" . $row ["user_science"] . "</text></row>";
}
$xml .= "</rows>";
echo '<root>'.$xml.'</root>';

[kyzy_yy_pm]

[Quote=引用 11 楼 chengcharect 的回复:]
Notice: /klmexam/admin/user_xml.php line 20 - Undefined variable: xml
[/Quote]

$xml = "<?xml version=\"1.0\"?><rows>";
while ( $row = $db->fetch_array ( $result ) ) {
$xml .= "<row><value>" . $row ["user_grade"] . "</value><text>" . $row ["user_science"] . "</text></row>";
}
$xml .= "</rows>";
echo '<root>'.$xml.'</root>';