Hi Timothy,
I added functionality to allow the <asp:RequiredFieldValidator> to work (client + server side) the new <ext:ComboBox>.
The following code sample demonstrates a simple <ext:ComboBox> with <asp:RequiredFieldValidator>.
Example
<ext:ComboBox
ID="ComboBox1"
runat="server">
<Items>
<ext:ListItem Text="Item0" />
<ext:ListItem Text="Item1" />
<ext:ListItem Text="Item2" />
<ext:ListItem Text="Item3" />
<ext:ListItem Text="Item4" />
</Items>
</ext:ComboBox>
<asp:RequiredFieldValidator
ID="RequiredFieldValidator1"
runat="server"
ControlToValidate="ComboBox1"
Display="Dynamic">!</asp:RequiredFieldValidator>
There is one problem that quickly becomes apparent with the above sample... the <ext:ComboBox> is treated as a block level element, so the RequiredFieldValidator error message is forced down into the next line if invalid.
I played around with the <ext:ComboBox> for a while and could not come up with a clean fix, other than adding the <ext:ComboBox> and <asp:RequiredFieldValidator> to separate cells (<td>) of an inline <table>. The following sample demonstrates.
Example
Choose Item:
<table style="display:inline;">
<tr>
<td>
<ext:ComboBox
ID="ComboBox1"
runat="server">
<Items>
<ext:ListItem Text="Item1" />
<ext:ListItem Text="Item2" />
<ext:ListItem Text="Item3" />
</Items>
</ext:ComboBox>
</td>
<td>
<asp:RequiredFieldValidator
ID="RequiredFieldValidator1"
runat="server"
ControlToValidate="ComboBox1"
Display="Dynamic">!</asp:RequiredFieldValidator>
</td>
</tr>
</table>
<asp:Button ID="Button1" runat="server" Text="Submit" onclick="Button1_Click" />
Clearly a pretty gross hack, but it works and might be acceptable until a cleaner css revision can be found.
Hope this helps.