force user select from autocomplete - asp.net

Question

i am beginner for asp.net . I now facing a problem . How can i force a user to select option from ajax control toolkit autocomplete?
Here is my sample code
<cus:cusTextBox ID="txtCMemberID" runat="server" Action="Edit"
CssClass="inputTextM" OnTextChanged="txtCMemberID_TextChanged"
AutoPostBack="True"></cus:cusTextBox>
<asp:AutoCompleteExtender ID="AutoCompleteExtender2" runat="server"
ServicePath="~/Module/Common/autoComplete/acLewreMember.asmx"
MinimumPrefixLength="1" ServiceMethod="GetSuggestedStrings"
TargetControlID="txtCMemberID" CompletionInterval="10"
CompletionSetCount="3" EnableCaching="true"
CompletionListCssClass="completionListElement"
CompletionListItemCssClass="listItem"
CompletionListHighlightedItemCssClass="highlightedListItem"
FirstRowSelected="True"
ShowOnlyCurrentWordInCompletionListItem="True">
</asp:AutoCompleteExtender>
As you see the textbox is a custom control. Is that any way to force user to select option from autocomplete?Please provide me a sample code also. thanks

Answer 1

ASP.NET includes a useful feature called a validator.
<asp:TextBox ID="TextBox2" ValidationGroup="Group2" runat="server" />
<asp:RequiredFieldValidator ID="RequiredFieldValidator2" ErrorMessage="*Required" ValidationGroup="Group2"
ControlToValidate="TextBox2" runat="server" />
<asp:Button ID="Button2" Text="Validate Group2"
ValidationGroup="Group2" runat="server" />
Here is the resource link for msdn: http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.requiredfieldvalidator.aspx
I'm not sure how these work with custom controls as I'm relatively new at asp. They also have a custom validator which might be more suited for your purposes, but like I said. I don't know exactly.
Note: If the client is using an old browser this won't work, so you also want to check on the server that this field isn't empty by using:
if (Page.IsValid)
{
//stuff to do in your event handler
}