asp validations for dynamic controls of web form

See more:

C#3.5

I'm creating dynamic controls of webform and also validations but those were not firing i kept validation group for a static button and required validation here is my code



switch (dr["DATATYPE"].ToString())
{
case "int":
case "string":
TextBox tb = new TextBox();
tb.ID = dr["FIELDNAME"].ToString();
td1.Controls.Add(tb);
if(flag=="show")
tb.Text = _frmElement.Element(dr["FIELDNAME"].ToString()).Value;
else if (flag == "new")
tb.Text = "";



//--- validations

if (dr["ISMANDATORY"].ToString() != (1).ToString())
{
RequiredFieldValidator rq = new RequiredFieldValidator();
rq.ControlToValidate = tb.ID;
rq.ErrorMessage = "This fields are required";
rq.ValidationGroup = "a";
}

//--validations
break;
<asp: button id="Btnsave" runat="server" validationgroup="a">


Why so im not able to do validations