Error when trying to populate listbox

Hi I am a student I am getting this error:

forreach statement cannot operate on variables of type 'object' because 'object' does not contain a public definition for 'GetEnumerat开发者_JAVA百科or'

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication5
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            string result = " ";
            foreach (string activity in listBox1.SelectedItems)
            {
                result += activity + "   ";
            }
            this.textBox1.Text = result;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            listBox1.Items.Add(textBox2.Text);
            textBox2.Clear();
        }
    }
}

Pl. help me

Your code works fine for me. However, your code will break if you've added something other than a string to your ListBox's Items collection (although this will produce a different error than what you're apparently seeing).

Can you add the code you use to populate this ListBox?