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Limit Number of items to be Selected in ASP.Net ListBox

February 9, 2016 Leave a comment

Hi all,

try this example to Limit Number of items to be Selected in ASP.Net ListBox using Client and Server side validation


<script type="text/javascript" language="javascript">
function CustomValidator1_ClientValidate(source,args)
{ 
var listbox = document.getElementById("<%=ListBox1.ClientID %>");
var total = 0;
var i=0;
for( i = 0; i < listbox.options.length; i++ )
{
 if (listbox.options[i].selected) 
 {
 total ++; 
 if (total >10) {
 args.IsValid = false;
 return;
 }
 } 
 } 
 args.IsValid = true; return;
}
</script>

<asp:ListBox ID="ListBox1" runat="server" SelectionMode="Multiple" Height="100%"
Width="100%"></asp:ListBox>
<asp:Button ID="btn_Save" runat="server" Text="Save" />
<asp:CustomValidator ID="CustomValidator1" runat="server" Display="Dynamic" ErrorMessage="Please select 10 items only."
ClientValidationFunction="CustomValidator1_ClientValidate" OnServerValidate="CustomValidator1_ServerValidate">
</asp:CustomValidator>

In Code behind :

protected void CustomValidator1_ServerValidate(object source, ServerValidateEventArgs args)
{
int count = 0;
for (int i = 0; i < ListBox1.Items.Count; i++)
{
if (ListBox1.Items[i].Selected)
count++;
}
args.IsValid = (count > 10) ? false : true;
}

Hope this helps

Good Luck

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