PopupControl is an ASP.NET AJAX extender that can be attached to any control in order to open a popup window that displays additional content. This popup window will probably be interactive and will probably be within an ASP.NET AJAX UpdatePanel, so it will be able to perform complex server-based processing (including postbacks) without affecting the rest of the page. The popup window can contain any content, including ASP.NET server controls, HTML elements, etc. Once the work of the popup window is done, a simple server-side call dismisses it and triggers any relevant script on the client to run and update the page dynamically.
TargetControlID——附加到的控件的ID
PopupControlID——弹出显示的控件ID
Position——弹出控件相对目标控件的位置（Left,Right, Top, Bottom, Center）
CommitProperty——目标控件要从弹出控件得到的属性值（可选）
CommotScript——获取弹出控件属性值的脚本
OffsetX/OffsetY——水平、竖直方向距默认位置的偏移距离
Animations
——OnShow
——OnHide
示例代码：
1 <asp:ScriptManager ID="ScriptManager1" runat="server" />
2 <div>
3 <br />
4 ToDo:
5 <asp:TextBox ID="MyTextBox" runat="server" Width="538px"></asp:TextBox>
6 <br />
7 <asp:Panel ID="Panel1" runat="server" CssClass="popupControl">
8 <asp:UpdatePanel ID="UpdatePanel1" runat="server">
9 <ContentTemplate>
10 <asp:RadioButtonList ID="RadioButtonList1" runat="server" AutoPostBack="true" OnSelectedIndexChanged="RadioButtonList1_SelectedIndexChanged"
11 Width="146px">
12 <asp:ListItem Text="Scott Guthrie" ></asp:ListItem>
13 <asp:ListItem Text="Simon Muzio"></asp:ListItem>
14 <asp:ListItem Text="Brian Goldfarb"></asp:ListItem>
15 <asp:ListItem Text="Joe Stagner"></asp:ListItem>
16 <asp:ListItem Text="Shawn Nandi"></asp:ListItem>
17 </asp:RadioButtonList>
18 </ContentTemplate>
19 </asp:UpdatePanel>
20 </asp:Panel>
21 <br />
22 <ajaxToolkit:PopupControlExtender ID="PopupControlExtender1" runat="server" CommitProperty="value"
23 CommitScript="e.value += ' - SEND A MEETING REQUEST!';" PopupControlID="Panel1"
24 Position="Bottom" TargetControlID="MyTextBox">
25 </ajaxToolkit:PopupControlExtender>
26
27 </div>
简单CSS
.popupControl
{
background-color:#AAD4FF;
position:absolute;
visibility:hidden;
border-style:solid;
border-color: Black;
border-width: 2px;
}