asp.net checkboxlist limit selection
CheckBoxList is an asp.net web server control which render a multi selection check box group on web page.
by default, users can select as many items as they want from a checkboxlist. but sometimes .net developers need to limit
checkboxlist items selection.
in this example, we limit the checkboxlist items selection to 3. that mean users can select up to 3 items from checkboxlist. to do this, we need to apply few steps. first we write an event handler for checkboxlist SelectedIndexChanged event. then we apply a linq query to populate an items collection from only checkboxlist selected items.
next we count the selected items collection's items. if the selected items are greater than 3 then we deselect the last selected item and display a message to user that you can select up to 3 items. finally it makes the checkboxlist selection limit to 3. checkboxlist items.Last().Selected provide us a way to get the checkboxlist last selected item.
the following asp.net c# example code demonstrate us how can we apply limit selection for a checkboxlist in an asp.net application.
in this example, we limit the checkboxlist items selection to 3. that mean users can select up to 3 items from checkboxlist. to do this, we need to apply few steps. first we write an event handler for checkboxlist SelectedIndexChanged event. then we apply a linq query to populate an items collection from only checkboxlist selected items.
next we count the selected items collection's items. if the selected items are greater than 3 then we deselect the last selected item and display a message to user that you can select up to 3 items. finally it makes the checkboxlist selection limit to 3. checkboxlist items.Last().Selected provide us a way to get the checkboxlist last selected item.
the following asp.net c# example code demonstrate us how can we apply limit selection for a checkboxlist in an asp.net application.
checkboxlist-limit-selection.aspx
<%@ Page Language="C#" AutoEventWireup="true"%>
<!DOCTYPE html>
<script runat="server">
protected void Page_Load(object sender, EventArgs e)
{
if(!Page.IsPostBack)
{
CheckBoxList1.Items.Add(new ListItem("Spotted Nutcracker", "1"));
CheckBoxList1.Items.Add(new ListItem("Alpine Chough", "2"));
CheckBoxList1.Items.Add(new ListItem("Green Magpie", "3"));
CheckBoxList1.Items.Add(new ListItem("Eurasian Jay", "4"));
CheckBoxList1.Items.Add(new ListItem("Carrion Crow", "5"));
}
}
protected void CheckBoxList1_SelectedIndexChanged(object sender, EventArgs e)
{
// linq query to find selected items from checkboxlist
var items = from ListItem li in CheckBoxList1.Items
where li.Selected == true
select li;
Label1.Text = "";
if(items.Count() > 3)
{
Label1.Text = "<b>checked maximum 3 items.</b><br />";
items.Last().Selected = false;
}
Label1.Text += "you checked item(s).....<br />";
foreach (ListItem li in items)
{
Label1.Text += li.Text+" | "+li.Value +"<br />";
}
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title>asp.net checkboxlist limit selection</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<h2 style="color:MidnightBlue; font-style:italic;">
asp.net example - checkboxlist limit selection
</h2>
<hr width="550" align="left" color="Gainsboro" />
<asp:Label
ID="Label1"
runat="server"
Text="check maximum 3 items from checkboxlist."
Font-Size="Medium"
Width="350"
>
</asp:Label>
<br /><br />
<asp:CheckBoxList
ID="CheckBoxList1"
runat="server"
RepeatLayout="Table"
RepeatColumns="2"
AutoPostBack="true"
OnSelectedIndexChanged="CheckBoxList1_SelectedIndexChanged"
>
</asp:CheckBoxList>
</div>
</form>
</body>
</html>
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