当文本框的模式设定为多行时，maxlength属性就无效了，这时可以使用RegularExpressionValidator控件，代码如下：

<

asp:TextBox 

ID

="txtIntroduct"

 runat

="server"

 TextMode

="MultiLine"

     Height

="120px"

 Width

="240px"

 class

="input_text"

 

/>

<

asp:RegularExpressionValidator 

ID

="RegularExpressionValidator2"

 ControlToValidate

="txtIntroduct"

     ValidationExpression

="([^.]|.){0,300}"

 runat

="server"

 SetFocusOnError

="true"

 Display

="None"

     ValidationGroup

="AddApply"

 ErrorMessage

="简单的介绍,300字以内!"

></

asp:RegularExpressionValidator

>

<

cc1:ValidatorCalloutExtender 

ID

="ValidatorCalloutExtender11"

 HighlightCssClass

="validatorCalloutHighlight"

     runat

="server"

 Enabled

="True"

 TargetControlID

="RegularExpressionValidator2"

>

</

cc1:ValidatorCalloutExtender

>

单行时就用maxlength属性//限制只能输入25个字

 <asp:TextBox ID="name" runat="server"  Width="350px"  MaxLength="25" ></asp:TextBox>