This is a short article describing how to implement validation for ASP.Net ListBox Control using Custom Validator in ASP.Net.
Validate at least one item is selected in ASP.Net ListBox Control
Below I have implemented an ASP.Net Custom Validator that checks whether use has selected atleast one item in the ASP.Net ListBox Control using ValidateListBox JavaScript method.
<asp:ListBox ID="ListBox1" runat="server" SelectionMode = "Multiple">
<asp:ListBox ID="ListBox1" runat="server" SelectionMode = "Multiple">
<asp:ListItem Text = "Apple" Value = "1"></asp:ListItem>
<asp:ListItem Text = "Mango" Value = "2"></asp:ListItem>
<asp:ListItem Text = "Orange" Value = "3"></asp:ListItem>
</asp:ListBox>
<asp:CustomValidator ID="CustomValidator1" runat="server" ErrorMessage="*Required"
ClientValidationFunction = "ValidateListBox"></asp:CustomValidator>
<script type = "text/javascript">
function ValidateListBox(sender, args) {
var options = document.getElementById("<%=ListBox1.ClientID%>").options;
for (var i = 0; i < options.length; i++) {
if (options[i].selected == true) {
args.IsValid = true;
return;
}
}
args.IsValid = false;
}
</script>
<asp:Button ID="Button1" runat="server" Text="Button" />
Validate at least one item present in ASP.Net ListBox Control
Below I have implemented an ASP.Net Custom Validator that checks whether ASP.Net ListBox Control contains at least one item using ValidateListBox JavaScript method.
<asp:ListBox ID="ListBox1" runat="server" SelectionMode = "Multiple">
</asp:ListBox>
<asp:CustomValidator ID="CustomValidator1" runat="server" ErrorMessage="*Required"
ClientValidationFunction = "ValidateListBox"></asp:CustomValidator>
<script type = "text/javascript">
function ValidateListBox(sender, args) {
var options = document.getElementById("<%=ListBox1.ClientID%>").options;
if (options.length > 0) {
args.IsValid = true;
}
else {
args.IsValid = false;
}
}
</script>
<asp:Button ID="Button1" runat="server" Text="Button" />
Hope you find the above code snippets useful.