customvalidator for dropdownlist not being invoked (apparently)

Question

Writing a custom validator for a dropdownlist that is using autopostback. Seems to ignore the validation altogether. Why is it ignored and is there an easy fix?

Note I did not use ControlToValidate

asp.net:

     <asp:UpdatePanel ID="updatePanel" runat="server" UpdateMode="Conditional" Visible="true" RenderMode="Inline">
        <ContentTemplate>
        <asp:DropDownList ID="ddlCommandAssign" runat="server" AutoPostBack="true">
        </asp:DropDownList>
          <asp:CustomValidator id="val_command_assigned" runat="server"  
          ErrorMessage="* " 
          display="Static"
          OnServerValidate="commandAssigned" 
          />
                </ContentTemplate>
       <Triggers>
            <asp:AsyncPostBackTrigger ControlID="ddlCommandAssign" 
                EventName="SelectedIndexChanged" />
        </Triggers>

    </asp:UpdatePanel>

Behind Code:

Sub commandAssigned(ByVal source As Object, _
  ByVal args As System.Web.UI.WebControls.ServerValidateEventArgs)

    Dim s As String
    s = ddlCommandAssign.SelectedValue
    'if s = "1" then 
    '  args.IsValid = true
    'else
    '  args.IsValid = False
    'end if
    args.IsValid = False
End Sub

For debugging purposes, I want it to fail every time.

It doesn't seem to be executing the behind code at all.

For debugging, I added the line response.redirect("dummy.html") ... which never gets called, which also indicates (I think) that the validator never gets called.

Answer 1

Remove the update panel and try to do the validation at client-side itself using javascript.

CLIENT-SIDE VALIDATION

JavaScript event definition,

 function ValidateFunction(sender,args) 
 {
   var ddlCommandAssign= document.getElementById('<%=ddlCommandAssign.ClientID %>');
    if (ddlCommandAssign.options[control.selectedIndex].value=='0') 
    {  args.IsValid = false;//This shows the validation error message and stops execution at client side itself.}
  else { args.IsValid = true;//This will return to the server side. }    
 }

Aspx section:

  <asp:DropDownList ID="DropDownList1" runat="server">
        <asp:ListItem Value="1">select</asp:ListItem>
        <asp:ListItem Value="2">sdasda</asp:ListItem>
    </asp:DropDownList>
    <asp:CustomValidator ID="valCustmID" runat="server" ErrorMessage="*" ForeColor="Red"
        ValidationGroup="group1" ClientValidationFunction="ValidateFunction"></asp:CustomValidator>
    <asp:Button ID="Button1" runat="server" Text="Button" ValidationGroup="group1" />

NOTE: Both the custom validator and the triggering button should have same validation group.

SERVER-SIDE VALIDATION

If you really want the validation server side see the code below:

     <asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <ContentTemplate>
            <asp:DropDownList ID="DropDownList1" runat="server">
                <asp:ListItem Value="1">select</asp:ListItem>
                <asp:ListItem Value="2">sdasda</asp:ListItem>
            </asp:DropDownList>
            <asp:CustomValidator ID="CustomValidator1" OnServerValidate="commandAssigned" runat="server" ErrorMessage="*" ValidationGroup="group1"></asp:CustomValidator>
            <asp:Button ID="Button1" runat="server" Text="Button" ValidationGroup="group1" />
        </ContentTemplate>
    </asp:UpdatePanel>

NOTE: Both the custom validator and the triggering button should have same validation group.

code behind event looks as below:

    protected void commandAssigned(object source, ServerValidateEventArgs args)
    {
        if (DropDownList1.SelectedItem.Value == "1")            
            args.IsValid = false;  //since you gave controlToValidate="DropDownList1"  this will display the error message.       
        else           
            args.IsValid = true;            
    }

Hope this helps..