RequiredFieldValidator for dropdownlist not work - asp.net

Question

what I do wrong?
<asp:Panel ID="pnlProductUnits" runat="server" Width="100%">
<asp:Repeater ID="repProductUnits" runat="server" EnableViewState="true" onitemcommand="Button_ItemCommand">
<HeaderTemplate>
<table class="grid" width="100%">
<tbody>
<tr>
<th align="left">test1</th>
<th align="left">test2</th>
<th align="left">test3</th>
<th width="50"></th>
</tr>
</tbody>
</HeaderTemplate>
<ItemTemplate>
<tr>
<td><%# ((DBData.Catalog.ProductU)Container.DataItem).PrimaryUnitName%>
</td>
<td align="center">
<%# ((DBData.Catalog.ProductU)Container.DataItem).SecondaryUnitName%>
</td>
<td align="center">
<%# ((DBData.Catalog.ProductU)Container.DataItem).Quantity%>
</td>
<td style="display:none">
<asp:Label ID="PrimaryUnitID" runat="server"
Text="<%# ((DBData.Catalog.ProductU)Container.DataItem).PrimaryUnitID%>">
</asp:Label>
<asp:Label ID="SecondaryUnitID" runat="server"
Text="<%# ((DBData.Catalog.ProductU)Container.DataItem).SecondaryUnitID%>">
</asp:Label>
</td>
<td align="center">
<asp:Button id="btRemove" runat="server" commandname="deleteProductUnit" Text="Delete">
</asp:Button>
</td>
</tr>
</ItemTemplate>
<FooterTemplate>
<tr>
<td>
<asp:DropDownList ID="ddlPrimaryUnit" runat="server" ValidationGroup="grpQuantity">
</asp:DropDownList>
<asp:RequiredFieldValidator runat="server" ErrorMessage="*"
Display="Dynamic" Text="*" ControlToValidate="ddlPrimaryUnit" ValidationGroup="grpQuantity" ForeColor="#FF3300">
</asp:RequiredFieldValidator>
</td>
<td>
<asp:DropDownList ID="ddlSecondaryUnit" runat="server" ValidationGroup="grpQuantity">
</asp:DropDownList>
<asp:RequiredFieldValidator runat="server" ErrorMessage="*" Display="Dynamic" Text="*" ControlToValidate="ddlSecondaryUnit" ValidationGroup="grpQuantity" ForeColor="#FF3300"></asp:RequiredFieldValidator>
</td>
<td>
<asp:TextBox ID="txtQuantity" runat="server" placeholder="select value" ClientIDMode="Static"></asp:TextBox>
<asp:RequiredFieldValidator runat="server" ErrorMessage="*" ControlToValidate="txtQuantity" ValidationGroup="grpQuantity" ForeColor="#FF3300"></asp:RequiredFieldValidator>
</td>
<td colspan="20">
<asp:Button id="btNew" runat="server" commandname="addProductUnit" Text="Add"
CommandArgument="test" ValidationGroup="grpQuantity"> </asp:Button>
</td>
</tr>
</table>
</FooterTemplate>
</asp:Repeater>
</asp:Panel>

Answer 1

I suspect your problem is related to the validator knowing what the DropDownList's original selection was and whether or not something has been selected. You may need to add an InitialValue to the required field validator.
<asp:RequiredFieldValidator ID="RequiredFieldValidator1"
runat="server" ErrorMessage="*" Display="Dynamic" Text="*"
ControlToValidate="ddlSecondaryUnit" ValidationGroup="grpQuantity"
ForeColor="#FF3300" InitialValue=""></asp:RequiredFieldValidator>
Depending on your DropDownList's datasource, that value may be something like "Please Select" or maybe just blank.