UpdatePanel刷新的问题

--------------------编程问答-------------------- <div>
        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
            <ContentTemplate>
               <asp:DropDownList ID="ddlLB" runat="server" Width="15%" AutoPostBack="True" OnSelectedIndexChanged="ddlLB_SelectedIndexChanged">
               </asp:DropDownList>
                 <asp:DropDownList ID="ddlChild" runat="server" Width="20%">
               </asp:DropDownList>
                 </ContentTemplate>
        </asp:UpdatePanel>
        </div> 没问题 --------------------编程问答--------------------



                    <div>

                 <asp:UpdatePanel ID="UpdatePanel2" runat="server">

                <ContentTemplate>

                        <asp:DropDownList ID="ddlLB" runat="server" Width="15%" AutoPostBack="True">

                         <asp:ListItem></asp:ListItem>

                        <asp:ListItem>家庭自用</asp:ListItem>

                        <asp:ListItem>非营业企业</asp:ListItem>

                        <asp:ListItem>非营业机关</asp:ListItem>

                        <asp:ListItem>非营业货车</asp:ListItem>

                        <asp:ListItem>营业租赁</asp:ListItem>

                        <asp:ListItem>营业公交</asp:ListItem>

                        <asp:ListItem>营业客运</asp:ListItem>

                        <asp:ListItem>营业货车</asp:ListItem>

                        <asp:ListItem>特种车</asp:ListItem>

                        </asp:DropDownList>

                    <asp:DropDownList ID="ddlChild" runat="server" Width="20%">

                    </asp:DropDownList>

                    </ContentTemplate>

                    </asp:UpdatePanel>

                    </div>

以上是您的代码，效果也是一样的，默认有CSS样式，选择一条数据后，CSS直接失效。

图片：

默认情况下

选择一条items后

--------------------编程问答-------------------- 做了一下,设置CSS如下:
.style1{ background-color:#ff0000;}
.style2{ background-color:#cccccc;}
没有失效!事实上也不可能失效!!不知道你哪里失效了??
也可把你的css贴一下!!

--------------------编程问答--------------------



/*Defaults Styling*/

body {font:12px/17px Arial, Helvetica, sans-serif; color:#333; background:#ccc; padding:40px 20px 20px 20px;}

fieldset {background:#f2f2e6; padding:10px; border:1px solid #fff; border-color:#fff #666661 #666661 #fff; margin-bottom:36px; width:600px;}

input, textarea, select {font:12px/12px Arial, Helvetica, sans-serif; padding:0;}

fieldset.action {background:#9da2a6; border-color:#e5e5e5 #797c80 #797c80 #e5e5e5; margin-top:-20px;}

legend {background:#bfbf30; color:#fff; font:17px/21px Calibri, Arial, Helvetica, sans-serif; padding:0 10px; margin:-26px 0 0 -11px; font-weight:bold; border:1px solid #fff; border-color:#e5e5c3 #505014 #505014 #e5e5c3;}

label {font-size:11px; font-weight:bold; color:#666;}

label.opt {font-weight:normal;}

dl {clear:both;}

dt {float:left; text-align:right; width:90px; line-height:25px; margin:0 10px 10px 0;}

dd {float:left; width:475px; line-height:25px; margin:0 0 10px 0;}

#footer {font-size:11px;}



#container {width:700px; margin:0 auto;}



/*Text inputs*/

.NFText {border:none; vertical-align:middle; font:12px/15px Arial, Helvetica, sans-serif; background:none;}

.NFTextCenter {height:15px; background:url(img/input.png) repeat-x 0 0; padding:3px 0; margin:0; float:left; line-height:15px;}

.NFTextLeft, .NFTextRight {width:7px; height:21px; vertical-align:middle; float:left;}

.NFTextLeft {background:url(img/input-left.png) no-repeat 0 0;}

.NFTextRight {background:url(img/input-right.png) no-repeat 0 0;}

/*Radio*/

.NFRadio {cursor:pointer; position:absolute; display:block; width:13px; height:13px; border:1px solid transparent; background:url(img/radio.png) no-repeat 0 0; z-index:2;}

/*Checkbox*/

.NFCheck {cursor:pointer; position:absolute; width:12px; height:12px; border:1px solid transparent; background:url(img/checkbox.png) no-repeat 0 0; z-index:2;}

/*Buttons*/

.NFButton {width:auto; height:26px; color:#fff; padding:0 2px; background:url(img/button.png) repeat-x 0 0; cursor:pointer; border:none; font:10px/26px Tahoma, Arial, Helvetica, sans-serif; font-weight:bold; text-transform:uppercase; letter-spacing:1px; vertical-align:middle;}

.NFButtonLeft, .NFButtonRight {width:6px; height:26px; vertical-align:middle;}

.NFButtonLeft {background:url(img/button-left.png) no-repeat 0 0;}

.NFButtonRight {background:url(img/button-right.png) no-repeat 0 0;}

/*Textareas*/

.NFTextarea {border:none; background:none; font:12px/12px Arial, Helvetica, sans-serif; margin:0;}

.NFTextareaTop, .NFTextareaBottom {height:5px; clear:both; float:none; padding-right:10px;}

.NFTextareaTop {background:url(img/textarea-tr.png) no-repeat 100% 0;}

.NFTextareaBottom {background:url(img/textarea-br.png) no-repeat 100% 0; margin-bottom:5px;}

.NFTextareaTopLeft, .NFTextareaBottomLeft {width:5px; height:5px;}

.NFTextareaTopLeft {background:#f2f2e6 url(img/textarea-tl.png) no-repeat 0 0;}

.NFTextareaBottomLeft {background:#f2f2e6 url(img/textarea-bl.png) no-repeat 0 0;}

.NFTextareaLeft, .NFTextareaRight, .NFTextareaLeftH, .NFTextareaRightH {float:left; padding-bottom:5px;}

.NFTextareaLeft, .NFTextareaLeftH {width:5px;}

.NFTextareaLeft {background:url(img/textarea-l-off.png) repeat-y 0 0;}

.NFTextareaLeftH {background:url(img/textarea-l-over.png) repeat-y 0 0;}

.NFTextareaRight, .NFTextareaRightH {padding-right:5px; padding-bottom:0;}

.NFTextareaRight {background:url(img/textarea-r-off.png) repeat-y 100% 0;}

.NFTextareaRightH {background:url(img/textarea-r-over.png) repeat-y 100% 100%;}

/*Files*/

.NFFileButton {padding-bottom:0; vertical-align:bottom; cursor:pointer; background:url(img/file.png) no-repeat 0 0; width:60px; height:21px;}

.NFFile {position:relative; margin-bottom:5px;}

.NFFile input.NFhidden {position:relative; filter:alpha(opacity=0); opacity:0; z-index:2; cursor:pointer; text-align:left;}

.NFFileNew {position:absolute; top:0px; left:0px; z-index:1;}

/*Selects*/

.NFSelect {height:21px; position:absolute; border:1px solid transparent;}

.NFSelectLeft {float:left; width:3px; height:21px; background:url(img/select-left.png) no-repeat 0 0; vertical-align:middle;}

.NFSelectRight {height:21px; width:auto; background:url(img/select-right.png) no-repeat 100% 0; cursor:pointer; font:12px/21px Arial, Helvetica, sans-serif; color:#fff; padding-left:3px; margin-left:3px;}

.NFSelectTarget {position:absolute; background:none; margin-left:-13px; margin-top:18px; z-index:3; left:0; top:0; padding-bottom:13px;}

.NFSelectOptions {position:relative; background:#707175; margin-left:16px; margin-top:0; list-style:none; padding:4px 0; color:#fff; font:11px/13px Arial, Helvetica, sans-serif; z-index:4; max-height:200px; overflow-y:auto; overflow-x:hidden; left:0; top:0;}

.NFSelectOptions li {padding-bottom:1px;}

.NFSelectOptions a {display:block; text-decoration:none; color:#fff; padding:2px 3px; background:none;}

.NFSelectOptions a.NFOptionActive {background:#464646;}

.NFSelectOptions a:hover {background:#333;}

/*Multiple Selects*/

.NFMultiSelect {border:0; background:none; margin:0;}

.NFMultiSelectTop, .NFMultiSelectBottom {height:5px; clear:both; float:none; padding-right:10px;}

.NFMultiSelectTop {background:url(img/textarea-tr.png) no-repeat 100% 0;}

.NFMultiSelectBottom {background:url(img/textarea-br.png) no-repeat 100% 0; margin-bottom:5px;}

.NFMultiSelectTopLeft, .NFMultiSelectBottomLeft {width:5px; height:5px;}

.NFMultiSelectTopLeft {background:#f2f2e6 url(img/textarea-tl.png) no-repeat 0 0;}

.NFMultiSelectBottomLeft {background:#f2f2e6 url(img/textarea-bl.png) no-repeat 0 0;}

.NFMultiSelectLeft, .NFMultiSelectRight, .NFMultiSelectLeftH, .NFMultiSelectRightH {float:left; padding-bottom:5px;}

.NFMultiSelectLeft, .NFMultiSelectLeftH {width:5px;}

.NFMultiSelectLeft {background:url(img/textarea-l-off.png) repeat-y 0 0;}

.NFMultiSelectLeftH {background:url(img/textarea-l-over.png) repeat-y 0 0;}

.NFMultiSelectRight, .NFMultiSelectRightH {padding-right:5px; padding-bottom:0;}

.NFMultiSelectRight {background:url(img/textarea-r-off.png) repeat-y 100% 0;}

.NFMultiSelectRightH {background:url(img/textarea-r-over.png) repeat-y 100% 0;}



/*Focused*/

.NFfocused {border:1px dotted #666;}

/*Hovered*/

.NFh {background-position:0 100%;}

.NFhr {background-position:100% 100%;}

/*Hidden*/

.NFhidden {opacity:0; z-index:-1; position:relative;}

/*Safari*/

select, input, textarea, button {outline:none; resize:none;}

--------------------编程问答--------------------



//Theme Variables - edit these to match your theme

var imagesPath = "img/";

var selectRightWidthSimple = 19;

var selectRightWidthScroll = 2;

var selectMaxHeight = 200;

var textareaTopPadding = 10;

var textareaSidePadding = 10;



//Global Variables

var NF = new Array();

var isIE = false;

var resizeTest = 1;



//Initialization function

function NFInit() {

	try {

		document.execCommand('BackgroundImageCache', false, true);

	} catch(e) {}

	if(!document.getElementById) {return false;}

	//alert("click me first");

	NFDo('start');

}

function NFDo(what) {

	var niceforms = document.getElementsByTagName('form');

	var identifier = new RegExp('(^| )'+'niceform'+'( |$)');

	if (/MSIE (\d+\.\d+);/.test(navigator.userAgent)) {

		var ieversion=new Number(RegExp.$1);

		if(ieversion < 7) {return false;} //exit script if IE6

		isIE = true;

	}

	for(var q = 0; q < niceforms.length; q++) {if(identifier.test(niceforms[q].className)) {

		if(what == "start") { //Load Niceforms

			NF[q] = new niceform(niceforms[q]);

			niceforms[q].start();

		}

		else { //Unload Niceforms

			niceforms[q].unload();

			NF[q] = "";

		}

	}}

}

function NFFix() {

	NFDo('stop');

	NFDo('start');

}

function niceform(nf) {

	nf._inputText = new Array(); nf._inputRadio = new Array(); nf._inputCheck = new Array(); nf._inputSubmit = new Array(); nf._inputFile = new Array(); nf._textarea = new Array(); nf._select = new Array(); nf._multiselect = new Array();

	nf.add_inputText = function(obj) {this._inputText[this._inputText.length] = obj; inputText(obj);}

	nf.add_inputRadio = function(obj) {this._inputRadio[this._inputRadio.length] = obj; inputRadio(obj);}

	nf.add_inputCheck = function(obj) {this._inputCheck[this._inputCheck.length] = obj; inputCheck(obj);}

	nf.add_inputSubmit = function(obj) {this._inputSubmit[this._inputSubmit.length] = obj; inputSubmit(obj);}

	nf.add_inputFile = function(obj) {this._inputFile[this._inputFile.length] = obj; inputFile(obj);}

	nf.add_textarea = function(obj) {this._textarea[this._textarea.length] = obj; textarea(obj);}

	nf.add_select = function(obj) {this._select[this._select.length] = obj; selects(obj);}

	nf.add_multiselect = function(obj) {this._multiselect[this._multiselect.length] = obj; multiSelects(obj);}

	nf.start = function() {

		//Separate and assign elements

		var allInputs = this.getElementsByTagName('input');

		for(var w = 0; w < allInputs.length; w++) {

			switch(allInputs[w].type) {

				case "text": case "password": {this.add_inputText(allInputs[w]); break;}

				case "radio": {this.add_inputRadio(allInputs[w]); break;}

				case "checkbox": {this.add_inputCheck(allInputs[w]); break;}

				case "submit": case "reset": case "button": {this.add_inputSubmit(allInputs[w]); break;}

				case "file": {this.add_inputFile(allInputs[w]); break;}

			}

		}

		var allButtons = this.getElementsByTagName('button');

		for(var w = 0; w < allButtons.length; w++) {

			this.add_inputSubmit(allButtons[w]);

		}

		var allTextareas = this.getElementsByTagName('textarea');

		for(var w = 0; w < allTextareas.length; w++) {

			this.add_textarea(allTextareas[w]);

		}

		var allSelects = this.getElementsByTagName('select');

		for(var w = 0; w < allSelects.length; w++) {

			if(allSelects[w].size == "1") {this.add_select(allSelects[w]);}

			else {this.add_multiselect(allSelects[w]);}

		}

		//Start

		for(w = 0; w < this._inputText.length; w++) {this._inputText[w].init();}

		for(w = 0; w < this._inputRadio.length; w++) {this._inputRadio[w].init();}

		for(w = 0; w < this._inputCheck.length; w++) {this._inputCheck[w].init();}

		for(w = 0; w < this._inputSubmit.length; w++) {this._inputSubmit[w].init();}

		for(w = 0; w < this._inputFile.length; w++) {this._inputFile[w].init();}

		for(w = 0; w < this._textarea.length; w++) {this._textarea[w].init();}

		for(w = 0; w < this._select.length; w++) {this._select[w].init(w);}

		for(w = 0; w < this._multiselect.length; w++) {this._multiselect[w].init(w);}

	}

	nf.unload = function() {

		//Stop

		for(w = 0; w < this._inputText.length; w++) {this._inputText[w].unload();}

		for(w = 0; w < this._inputRadio.length; w++) {this._inputRadio[w].unload();}

		for(w = 0; w < this._inputCheck.length; w++) {this._inputCheck[w].unload();}

		for(w = 0; w < this._inputSubmit.length; w++) {this._inputSubmit[w].unload();}

		for(w = 0; w < this._inputFile.length; w++) {this._inputFile[w].unload();}

		for(w = 0; w < this._textarea.length; w++) {this._textarea[w].unload();}

		for(w = 0; w < this._select.length; w++) {this._select[w].unload();}

		for(w = 0; w < this._multiselect.length; w++) {this._multiselect[w].unload();}

	}

}

function inputText(el) { //extent Text inputs

	el.oldClassName = el.className;

	el.left = document.createElement('img');

	el.left.src = imagesPath + "0.png";

	el.left.className = "NFTextLeft";

	el.right = document.createElement('img');

	el.right.src = imagesPath + "0.png";

	el.right.className = "NFTextRight";

	el.dummy = document.createElement('div');

	el.dummy.className = "NFTextCenter";

	el.onfocus = function() {

		this.dummy.className = "NFTextCenter NFh";

		this.left.className = "NFTextLeft NFh";

		this.right.className = "NFTextRight NFh";

	}

	el.onblur = function() {

		this.dummy.className = "NFTextCenter";

		this.left.className = "NFTextLeft";

		this.right.className = "NFTextRight";

	}

	el.init = function() {

		this.parentNode.insertBefore(this.left, this);

		this.parentNode.insertBefore(this.right, this.nextSibling);

		this.dummy.appendChild(this);

		this.right.parentNode.insertBefore(this.dummy, this.right);

		this.className = "NFText";

	}

	el.unload = function() {

		this.parentNode.parentNode.appendChild(this);

		this.parentNode.removeChild(this.left);

		this.parentNode.removeChild(this.right);

		this.parentNode.removeChild(this.dummy);

		this.className = this.oldClassName;

	}

}

--------------------编程问答--------------------



function inputRadio(el) { //extent Radio buttons

	el.oldClassName = el.className;

	el.dummy = document.createElement('div');

	if(el.checked) {el.dummy.className = "NFRadio NFh";}

	else {el.dummy.className = "NFRadio";}

	el.dummy.ref = el;

	if(isIE == false) {el.dummy.style.left = findPosX(el) + 'px'; el.dummy.style.top = findPosY(el) + 'px';}

	else {el.dummy.style.left = findPosX(el) + 4 + 'px'; el.dummy.style.top = findPosY(el) + 4 + 'px';}

	el.dummy.onclick = function() {

		if(!this.ref.checked) {

			var siblings = getInputsByName(this.ref.name);

			for(var q = 0; q < siblings.length; q++) {

				siblings[q].checked = false;

				siblings[q].dummy.className = "NFRadio";

			}

			this.ref.checked = true;

			this.className = "NFRadio NFh";

		}

	}

	el.onclick = function() {

		if(this.checked) {

			var siblings = getInputsByName(this.name);

			for(var q = 0; q < siblings.length; q++) {

				siblings[q].dummy.className = "NFRadio";

			}

			this.dummy.className = "NFRadio NFh";

		}

	}

	el.onfocus = function() {this.dummy.className += " NFfocused";}

	el.onblur = function() {this.dummy.className = this.dummy.className.replace(/ NFfocused/g, "");}

	el.init = function() {

		this.parentNode.insertBefore(this.dummy, this);

		el.className = "NFhidden";

	}

	el.unload = function() {

		this.parentNode.removeChild(this.dummy);

		this.className = this.oldClassName;

	}

}

function inputCheck(el) { //extend Checkboxes

	el.oldClassName = el.className;

	el.dummy = document.createElement('img');

	el.dummy.src = imagesPath + "0.png";

	if(el.checked) {el.dummy.className = "NFCheck NFh";}

	else {el.dummy.className = "NFCheck";}

	el.dummy.ref = el;

	if(isIE == false) {el.dummy.style.left = findPosX(el) + 'px'; el.dummy.style.top = findPosY(el) + 'px';}

	else {el.dummy.style.left = findPosX(el) + 4 + 'px'; el.dummy.style.top = findPosY(el) + 4 + 'px';}

	el.dummy.onclick = function() {

		if(!this.ref.checked) {

			this.ref.checked = true;

			this.className = "NFCheck NFh";

		}

		else {

			this.ref.checked = false;

			this.className = "NFCheck";

		}

	}

	el.onclick = function() {

		if(this.checked) {this.dummy.className = "NFCheck NFh";}

		else {this.dummy.className = "NFCheck";}

	}

	el.onfocus = function() {this.dummy.className += " NFfocused";}

	el.onblur = function() {this.dummy.className = this.dummy.className.replace(/ NFfocused/g, "");}

	el.init = function() {

		this.parentNode.insertBefore(this.dummy, this);

		el.className = "NFhidden";

	} 

	el.unload = function() {

		this.parentNode.removeChild(this.dummy);

		this.className = this.oldClassName;

	}

}

function inputSubmit(el) { //extend Buttons

	el.oldClassName = el.className;

	el.left = document.createElement('img');

	el.left.className = "NFButtonLeft";

	el.left.src = imagesPath + "0.png";

	el.right = document.createElement('img');

	el.right.src = imagesPath + "0.png";

	el.right.className = "NFButtonRight";

	el.onmouseover = function() {

		this.className = "NFButton NFh";

		this.left.className = "NFButtonLeft NFh";

		this.right.className = "NFButtonRight NFh";

	}

	el.onmouseout = function() {

		this.className = "NFButton";

		this.left.className = "NFButtonLeft";

		this.right.className = "NFButtonRight";

	}

	el.init = function() {

		this.parentNode.insertBefore(this.left, this);

		this.parentNode.insertBefore(this.right, this.nextSibling);

		this.className = "NFButton";

	}

	el.unload = function() {

		this.parentNode.removeChild(this.left);

		this.parentNode.removeChild(this.right);

		this.className = this.oldClassName;

	}

}

function inputFile(el) { //extend File inputs

	el.oldClassName = el.className;

	el.dummy = document.createElement('div');

	el.dummy.className = "NFFile";

	el.file = document.createElement('div');

	el.file.className = "NFFileNew";

	el.center = document.createElement('div');

	el.center.className = "NFTextCenter";

	el.clone = document.createElement('input');

	el.clone.type = "text";

	el.clone.className = "NFText";

	el.clone.ref = el;

	el.left = document.createElement('img');

	el.left.src = imagesPath + "0.png";

	el.left.className = "NFTextLeft";

	el.button = document.createElement('img');

	el.button.src = imagesPath + "0.png";

	el.button.className = "NFFileButton";

	el.button.ref = el;

	el.button.onclick = function() {this.ref.click();}

	el.init = function() {

		var top = this.parentNode;

		if(this.previousSibling) {var where = this.previousSibling;}

		else {var where = top.childNodes[0];}

		top.insertBefore(this.dummy, where);

		this.dummy.appendChild(this);

		this.center.appendChild(this.clone);

		this.file.appendChild(this.center);

		this.file.insertBefore(this.left, this.center);

		this.file.appendChild(this.button);

		this.dummy.appendChild(this.file);

		this.className = "NFhidden";

		this.relatedElement = this.clone;

	}

	el.unload = function() {

		this.parentNode.parentNode.appendChild(this);

		this.parentNode.removeChild(this.dummy);

		this.className = this.oldClassName;

	}

	el.onchange = el.onmouseout = function() {this.relatedElement.value = this.value;}

	el.onfocus = function() {

		this.left.className = "NFTextLeft NFh";

		this.center.className = "NFTextCenter NFh";

		this.button.className = "NFFileButton NFh";

	}

	el.onblur = function() {

		this.left.className = "NFTextLeft";

		this.center.className = "NFTextCenter";

		this.button.className = "NFFileButton";

	}

	el.onselect = function() {

		this.relatedElement.select();

		this.value = '';

	}

}

function textarea(el) { //extend Textareas

	el.oldClassName = el.className;

	el.height = el.offsetHeight - textareaTopPadding;

	el.width = el.offsetWidth - textareaSidePadding;

	el.topLeft = document.createElement('img');

	el.topLeft.src = imagesPath + "0.png";

	el.topLeft.className = "NFTextareaTopLeft";

	el.topRight = document.createElement('div');

	el.topRight.className = "NFTextareaTop";

	el.bottomLeft = document.createElement('img');

	el.bottomLeft.src = imagesPath + "0.png";

	el.bottomLeft.className = "NFTextareaBottomLeft";

	el.bottomRight = document.createElement('div');

	el.bottomRight.className = "NFTextareaBottom";

	el.left = document.createElement('div');

	el.left.className = "NFTextareaLeft";

	el.right = document.createElement('div');

	el.right.className = "NFTextareaRight";

	el.init = function() {

		var top = this.parentNode;

		if(this.previousSibling) {var where = this.previousSibling;}

		else {var where = top.childNodes[0];}

		top.insertBefore(el.topRight, where);

		top.insertBefore(el.right, where);

		top.insertBefore(el.bottomRight, where);

		this.topRight.appendChild(this.topLeft);

		this.right.appendChild(this.left);

		this.right.appendChild(this);

		this.bottomRight.appendChild(this.bottomLeft);

		el.style.width = el.topRight.style.width = el.bottomRight.style.width = el.width + 'px';

		el.style.height = el.left.style.height = el.right.style.height = el.height + 'px';

		this.className = "NFTextarea";

	}

	el.unload = function() {

		this.parentNode.parentNode.appendChild(this);

		this.parentNode.removeChild(this.topRight);

		this.parentNode.removeChild(this.bottomRight);

		this.parentNode.removeChild(this.right);

		this.className = this.oldClassName;

		this.style.width = this.style.height = "";

	}

	el.onfocus = function() {

		this.topLeft.className = "NFTextareaTopLeft NFh";

		this.topRight.className = "NFTextareaTop NFhr";

		this.left.className = "NFTextareaLeftH";

		this.right.className = "NFTextareaRightH";

		this.bottomLeft.className = "NFTextareaBottomLeft NFh";

		this.bottomRight.className = "NFTextareaBottom NFhr";

	}

	el.onblur = function() {

		this.topLeft.className = "NFTextareaTopLeft";

		this.topRight.className = "NFTextareaTop";

		this.left.className = "NFTextareaLeft";

		this.right.className = "NFTextareaRight";

		this.bottomLeft.className = "NFTextareaBottomLeft";

		this.bottomRight.className = "NFTextareaBottom";

	}

}

补充：.NET技术 ,  ASP.NET