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How to add an item to ListBox programmatically in asp.net c#

Add an item (ListItem) to ListBox
The following asp.net c# example code demonstrate us how can we add an item to ListBox control programmatically at run time. ListBox is an asp.net list web server control. ListBox contain items collection. Each item of ListBox control represent a ListItem object. We can add ListItem object to ListBox control's items collection both statically and programmatically.

To add an item to ListBox control programmatically, we can call the Collection<T> Class Add() method. This Add() method allow us to add an item to a collection. So we can easily add an item to ListBox control as ListBoxID.Items.Add(ListItem). Because ListBox contains items collection which support addition of new item.

To Add an item (ListItem) to a ListBox control, first we need to create the ListItem object. Each ListItem object have a Text property and optionally a Value property. We can also set the specified ListItem object Selected property value to true. After creating a ListItem object, we can add it to ListBox control by calling Add() method.
ListBoxAddListItem.aspx

<%@ Page Language="C#" %>

<!DOCTYPE html>

<script runat="server">
    protected void Button1_Click(object sender, System.EventArgs e) {
        ListBox1.Items.Add(new ListItem(TextBox1.Text));
        Response.Write("Item Added: " + TextBox1.Text);
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>ListBox example: how to add ListItem dynamically</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:Label ID="Label1" runat="server" Text="Controls" AssociatedControlID="ListBox1"></asp:Label>
        <asp:ListBox ID="ListBox1" runat="server">
            <asp:ListItem>Calendar</asp:ListItem>
            <asp:ListItem>Panel</asp:ListItem>
            <asp:ListItem>BulletedList</asp:ListItem>
            <asp:ListItem>AdRotator</asp:ListItem>
            <asp:ListItem>DropDownList</asp:ListItem>
            <asp:ListItem>ListBox</asp:ListItem>
            <asp:ListItem>Button</asp:ListItem>
        </asp:ListBox>
        <hr />
        <asp:Label ID="Label2" runat="server" Text="Input Item Text" AssociatedControlID="TextBox1"></asp:Label>
        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="TextBox1" Text="*"></asp:RequiredFieldValidator>
        <asp:Button ID="Button1" runat="server" Text="Add Item" OnClick="Button1_Click" />
    </div>
    </form>
</body>
</html>
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