探討這個問題的起因是CSDN論壇的一個帖子：
http://community.csdn.net/Expert/TopicView.asp?id=5460832
查看客戶端生成的HTML代碼可以看出，每次點擊都執行一次__doPostBack，並且將選擇項的參數傳遞到隱藏表單域之中。 當然，通過腳本和自己的隱藏域可以很輕鬆得到選擇項，但完全在服務器端，也可以得到。
<form name="MengXianhui" method="post" action="a.aspx?ddfg" id="MengXianhui">
<input type="hidden" name="__EVENTTARGET" value="" />
<input type="hidden" name="__EVENTARGUMENT" value="" />
<input type="hidden" name="__VIEWSTATE" value="dDw0NjI1MDk1MzQ7O2w8Q2hlY2tCb3hMaXN0MTowO0NoZWNrQm94TGlzdDE6MTtDaGVja0JveExpc3QxOjI7Q2hlY2tCb3hMaXN0 MTozO0NoZWNrQm94TGlzdDE6NDtDaGVja0JveExpc3QxOjQ7Pj6h9p2gvuU8iLKlA4DU0GtLAoZhCw==" />
<script language="javascript" type="text/javascript">
<!--
function __doPostBack(eventTarget, eventArgument) {
var theform;
if (window.navigator.appName.toLowerCase().indexOf("microsoft") > -1) {
theform = document.MengXianhui;
}
else {
theform = document.forms["MengXianhui"];
}
theform.__EVENTTARGET.value = eventTarget.split("$").join(":");
theform.__EVENTARGUMENT.value = eventArgument;
theform.submit();
}
// -->
</script>
<div style="padding:20px">
<table id="CheckBoxList1" border="0">
<tr>
<td><input id="CheckBoxList1_0" type="checkbox" name="CheckBoxList1:0" onclick="__doPostBack('CheckBoxList1$0','') " language="javascript" /><label for="CheckBoxList1_0">a</label></td>
</tr><tr>
<td><input id="CheckBoxList1_1" type="checkbox" name="CheckBoxList1:1" onclick="__doPostBack('CheckBoxList1$1','')" language="javascript" /><label for="CheckBoxList1_1">b</label></td>
</tr><tr>
<td><input id="CheckBoxList1_2" type="checkbox" name="CheckBoxList1:2" checked="checked" onclick="__doPostBack('CheckBoxList1$2','') " language="javascript" /><label for="CheckBoxList1_2">c</label></td>
</tr><tr>
<td><input id="CheckBoxList1_3" type="checkbox" name="CheckBoxList1:3" checked="checked" onclick="__doPostBack('CheckBoxList1$3','')" language="javascript" /><label for="CheckBoxList1_3">d</label></td>
</tr><tr>
<td><input id="CheckBoxList1_4" type="checkbox" name="CheckBoxList1:4" onclick="__doPostBack('CheckBoxList1$4','') " language="javascript" /><label for="CheckBoxList1_4">e</label></td>
</tr>
</table>
</div>
</form>
<input type="hidden" name="__EVENTTARGET" value="" />
<input type="hidden" name="__EVENTARGUMENT" value="" />
<input type="hidden" name="__VIEWSTATE" value="dDw0NjI1MDk1MzQ7O2w8Q2hlY2tCb3hMaXN0MTowO0NoZWNrQm94TGlzdDE6MTtDaGVja0JveExpc3QxOjI7Q2hlY2tCb3hMaXN0 MTozO0NoZWNrQm94TGlzdDE6NDtDaGVja0JveExpc3QxOjQ7Pj6h9p2gvuU8iLKlA4DU0GtLAoZhCw==" />
<script language="javascript" type="text/javascript">
<!--
function __doPostBack(eventTarget, eventArgument) {
var theform;
if (window.navigator.appName.toLowerCase().indexOf("microsoft") > -1) {
theform = document.MengXianhui;
}
else {
theform = document.forms["MengXianhui"];
}
theform.__EVENTTARGET.value = eventTarget.split("$").join(":");
theform.__EVENTARGUMENT.value = eventArgument;
theform.submit();
}
// -->
</script>
<div style="padding:20px">
<table id="CheckBoxList1" border="0">
<tr>
<td><input id="CheckBoxList1_0" type="checkbox" name="CheckBoxList1:0" onclick="__doPostBack('CheckBoxList1$0','') " language="javascript" /><label for="CheckBoxList1_0">a</label></td>
</tr><tr>
<td><input id="CheckBoxList1_1" type="checkbox" name="CheckBoxList1:1" onclick="__doPostBack('CheckBoxList1$1','')" language="javascript" /><label for="CheckBoxList1_1">b</label></td>
</tr><tr>
<td><input id="CheckBoxList1_2" type="checkbox" name="CheckBoxList1:2" checked="checked" onclick="__doPostBack('CheckBoxList1$2','') " language="javascript" /><label for="CheckBoxList1_2">c</label></td>
</tr><tr>
<td><input id="CheckBoxList1_3" type="checkbox" name="CheckBoxList1:3" checked="checked" onclick="__doPostBack('CheckBoxList1$3','')" language="javascript" /><label for="CheckBoxList1_3">d</label></td>
</tr><tr>
<td><input id="CheckBoxList1_4" type="checkbox" name="CheckBoxList1:4" onclick="__doPostBack('CheckBoxList1$4','') " language="javascript" /><label for="CheckBoxList1_4">e</label></td>
</tr>
</table>
</div>
</form>
在服務器端得到選擇項的做法是分析事件的參數，通過提交過來的事件參數得到。代碼如下：
<%@ Page Language="C#" AutoEventWireup="true" EnableViewState="false" Debug="true" % >
<!DOCTYPE html PUBLIC " -//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1- transitional.dtd">
<script runat="server">
void BoxList1_SelectedIndexChanged(object sender, System.EventArgs e)
{
//得到觸發事件的選擇項
string ClickedItem = Request.Form["__EVENTTARGET"];
ClickedItem = ClickedItem.Split(':')[1];
int index = Int32.Parse(ClickedItem );
Response.Write(CheckBoxList1.Items [index].Text);
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>在服務器端得到CheckBoxList 最好所選擇項的方法</title>
</head>
<body>
<form id="MengXianhui" runat="server">
<div style="padding:20px">
<asp:CheckBoxList AutoPostBack="true" ID="CheckBoxList1" runat="server"
OnSelectedIndexChanged="BoxList1_SelectedIndexChanged">
<asp:ListItem Value="1">a</asp:ListItem>
<asp:ListItem>b</asp:ListItem>
<asp:ListItem>c</asp:ListItem>
<asp:ListItem>d</asp:ListItem>
<asp:ListItem>e</asp:ListItem>
</asp:CheckBoxList>
</div>
</form>
</body>
</html>
<!DOCTYPE html PUBLIC " -//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1- transitional.dtd">
<script runat="server">
void BoxList1_SelectedIndexChanged(object sender, System.EventArgs e)
{
//得到觸發事件的選擇項
string ClickedItem = Request.Form["__EVENTTARGET"];
ClickedItem = ClickedItem.Split(':')[1];
int index = Int32.Parse(ClickedItem );
Response.Write(CheckBoxList1.Items [index].Text);
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>在服務器端得到CheckBoxList 最好所選擇項的方法</title>
</head>
<body>
<form id="MengXianhui" runat="server">
<div style="padding:20px">
<asp:CheckBoxList AutoPostBack="true" ID="CheckBoxList1" runat="server"
OnSelectedIndexChanged="BoxList1_SelectedIndexChanged">
<asp:ListItem Value="1">a</asp:ListItem>
<asp:ListItem>b</asp:ListItem>
<asp:ListItem>c</asp:ListItem>
<asp:ListItem>d</asp:ListItem>
<asp:ListItem>e</asp:ListItem>
</asp:CheckBoxList>
</div>
</form>
</body>
</html>