<%@ Register
Assembly="AjaxControlToolkit"
Namespace="AjaxControlToolkit"
TagPrefix="ajaxToolkit" %>

<form id="form1" runat="server">
<ajaxToolkit:ToolkitScriptManager runat="Server" ID="ScriptManager1" />

<table style="width: 98%">
<tr>
<td>
<asp:UpdatePanel ID="UpdatePanel1" runat="server" >
<ContentTemplate>

...其中页面使用ajaxToolkit:TextBoxWatermarkExtender

达到点击可输入,移开显示默认值的效果

<tr>
<td class="style1">
用户数<font color="red">*</font>:</td>
<td class="style2" colspan="2">
<asp:TextBox ID="TextBoxUserCount" runat="server" MaxLength="10"
Width="250px"></asp:TextBox>
<ajaxToolkit:TextBoxWatermarkExtender ID="TextBoxUserCount_TextBoxWatermarkExtender"
runat="server" TargetControlID="TextBoxUserCount"
WatermarkCssClass="Watermark" WatermarkText="请输入正整数">
</ajaxToolkit:TextBoxWatermarkExtender>
</td>
<td class="style1">
&nbsp;</td>
<td class="style1">
&nbsp;</td>
<td class="style1">
&nbsp;</td>
</tr>

</ContentTemplate> </asp:UpdatePanel>