How to access c# function in gridview

  protected String GetEncryptedString(String strNormalString)
    {
        return Server.UrlEncode(Encryption.Encrypt(strNormalString));
    }
  <asp:TemplateField>
   <ItemStyle HorizontalAlign="Center" VerticalAlign="Middle" Width="8%" />
   <HeaderStyle HorizontalAlign="Center" VerticalAlign="Middle" Width="8%" />
    <ItemTemplate>
     <a href="MyRequestDetail.aspx?ServiceRequestId=<%# GetEncryptedString(Eval("RequestId").ToString()) %>"><img src="../../../images/81_edit.png" /></a>
    </ItemTemplate>
   </asp:TemplateField>