add text file to listbox c#
OpenFileDialog f = new OpenFileDialog();
    if (f.ShowDialog() ==DialogResult.OK)
    {
        listBox1.Items.Clear();
        List<string> lines = new List<string>();
        using (StreamReader r = new StreamReader(f.OpenFile()))
        {
            string line;
            while ((line = r.ReadLine()) != null)
            {
                listBox1.Items.Add(line);
            }
        }
    }
