Question

I want to make a validation on the name, to force the user to input his name in four sections (four names). How to do that on the client side, using asp.net validation?

<td style="text-align: right;" class="style1">
    <asp:TextBox ID="txt_addName" runat="server" Width="220px" ValidationGroup="add"></asp:TextBox>
    <cc1:TextBoxWatermarkExtender ID="txt_addName_TextBoxWatermarkExtender" 
        runat="server" Enabled="True" TargetControlID="txt_addName"
        WatermarkText="أدخل اسم المحاضر رباعيا" WatermarkCssClass="watermark">
    </cc1:TextBoxWatermarkExtender>
    &nbsp;
    <asp:RequiredFieldValidator ID="RequiredFieldValidator4" runat="server" 
         ControlToValidate="txt_addName" Display="Dynamic" ErrorMessage="!"     
         ValidationGroup="add"></asp:RequiredFieldValidator>
    <asp:RegularExpressionValidator ID="RegularExpressionValidator2" runat="server" ErrorMessage="*"
        ValidationExpression="^(?:\p{L}+\s+){3}\p{L}+$" ControlToValidate="txt_addName"
        Display="Dynamic" ValidationGroup="add">يجب أن يكون اسم المحاضر رباعيا 
    </asp:RegularExpressionValidator>
</td>
<td style="text-align: center; width: 550px;">
     <asp:Button ID="btn_addNewLecterer" runat="server" Font-Bold="True" Font-Names="Garamond"
          Font-Size="Medium" Text="أضف محاضر جديد" OnClick="btn_addNewLecterer_Click" ValidationGroup="add" />
</td>

Answer 1

Something like this should work:

^(?:\p{L}+\s+){3,}\p{L}+\s*$

Explanation:

^      // start at the beginning of the string
(?:    // start a non-capturing group
\p{L}  // match any unicode letter...
+      // ...at least one of them...
\s+    // ...followed by at least one white-space character
)      // end the non-capturing group
{3,}   // repeat the group at least three times
\p{L}+ // finish with at least one unicode character...
\s*    // ...that can optionally be followed by white-space...
 $     // ...and then the string should end

If you want to limit the expression to require exactly four sections (I interpreted the question as requiring at least four), you change it to:

^(?:\p{L}+\s+){3}\p{L}+$