   private void button4_Click(object sender, EventArgs e)
        {
            listBox1.Items.Clear();
            if (textBox1.Text != "")
            {
                listBox1.Show();
                if (Directory.Exists(textBox1.Text))
                {
                    string[] files = Directory.GetFiles(textBox1.Text);
                    foreach (string file in files)
                        listBox1.Items.Add(file);

                }
                else
                    MessageBox.Show("Directory not exists");
            }
            else
                MessageBox.Show("Please enter directory name in  textBox1");

        }

     