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How to use CheckBoxList SelectedIndexChanged event in asp.net c#

CheckBoxList SelectedIndexChanged Event
asp.net checkboxlist web server control provides a multi selection checkbox group. this is a list server control. list server control contains an Items collection that hold all ListItem Objects. ListItem object have three useful properties they are Text, Value and Selected.

checkboxlist control's OnSelectedIndexChanged property raises the SelectedIndexChanged event. this property allow the developers to write a custom handler for SelectedIndexChanged event.

SelectedIndexChanged event raised when the selection from the cheeckboxlist control changes between posts to the server. so when a user change a selection from checkboxlist control then the SelectedIndexChanged event raised and the page automatically post to the web server. for that happening developers need to set checkboxlist AutoPostBack property value to True. when someone change the selection from checkboxlist then the page can immediately show the result using SelectedIndexChanged event.

the following c# example source code demonstrate us how can we use SelectedIndexChanged event in asp.net checkboxlist sever control.
CheckBoxListOnSelectedIndexChanged.aspx
<%@ Page Language="C#" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<script runat="server">
    protected void CheckBoxList1_SelectedIndexChnaged(object sender, System.EventArgs e)
    {
        Label1.Text = "You Choose Color:<br /><i>";
        foreach (ListItem li in CheckBoxList1.Items)
        {
            if (li.Selected == true)
            {
                Label1.Text += li.Text + "<br />";
            }
        }
        Label1.Text += "</i>";
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>How to use SelectedIndexChanged event in CheckBoxList</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <h2 style="color:Navy">CheckBoxList: OnSelectedIndexChanged</h2>
        <asp:Label 
             ID="Label1"
             runat="server"
             Font-Bold="true"
             ForeColor="Crimson"
             Font-Size="Large"
             >
        </asp:Label>
        <br />
        <asp:Label 
             ID="Label2"
             runat="server"
             Font-Bold="true"
             ForeColor="DarkBlue"
             Text="Color List"
             >
        </asp:Label>
        <asp:CheckBoxList 
             ID="CheckBoxList1"
             runat="server"
             AutoPostBack="true"
             OnSelectedIndexChanged="CheckBoxList1_SelectedIndexChnaged"
             BackColor="DodgerBlue"
             ForeColor="FloralWhite"
             >
             <asp:ListItem>AntiqueWhite</asp:ListItem>
             <asp:ListItem>Ivory</asp:ListItem>
             <asp:ListItem>DarkViolet</asp:ListItem>
             <asp:ListItem>Lavender</asp:ListItem>
             <asp:ListItem>DeepPink</asp:ListItem>
        </asp:CheckBoxList>
    </div>
    </form>
</body>
</html>
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