silverlight - How to add an item to a ListBox programmatically

how to add ListBox Item programmatically in silverlight
MainPage.xaml

<UserControl x:Class="SilverlightApps.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="600" 
    d:DesignWidth="800" 
    xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk">

    <Grid x:Name="LayoutRoot" Background="White">
        <sdk:Label 
            HorizontalAlignment="Left" 
            Margin="12,21,0,0" 
            Name="label1" 
            VerticalAlignment="Top" 
            Width="750"
            Content="Silverlight - how to add ListBox Item programmatically"
            FontSize="25"
            FontStyle="Italic"
            Foreground="MidnightBlue"
            />

        <ListBox 
            Height="100" 
            HorizontalAlignment="Left" 
            Margin="250,99,0,0" 
            Name="listBox1" 
            VerticalAlignment="Top" 
            Width="120"
            >
            <ListBoxItem Content="Bangladesh"></ListBoxItem>
            <ListBoxItem Content="Africa"></ListBoxItem>
            <ListBoxItem Content="Australia"></ListBoxItem>
        </ListBox>

        <Button 
            Content="Click Here To Add A New ListBox Item" 
            Height="23" 
            HorizontalAlignment="Left" 
            Margin="182,258,0,0" 
            Name="button1" 
            VerticalAlignment="Top" 
            Click="button1_Click"
            />
    </Grid>
</UserControl>
MainPage.xaml.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace SilverlightApps
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            ListBoxItem lbi = new ListBoxItem();
            lbi.Content = "United States";
            listBox1.Items.Add(lbi);
        }
    }
}
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