C# WPF ListBox Open files and save opened file path

private void listbox1_DragEnter(object sender, DragEventArgs e)
       {
           if (e.Data.GetDataPresent(DataFormats.FileDrop))
               e.Effects = DragDropEffects.All;
           else
               e.Effects = DragDropEffects.None;

       }

       private void listbox1_Drop(object sender, DragEventArgs e)
       {
           string[] s = (string[])e.Data.GetData(DataFormats.FileDrop, false);
           int i;

           for (i = 0; i < s.Length; i++)
               listbox1.Items.Add(s[i]);



           for (i = 0; i < s.Length; i++)
               listbox1.Items.Add(System.IO.Path.GetFileNameWithoutExtension(s[i]));

           if (e.Data.GetDataPresent(DataFormats.FileDrop))
           {


           }
       }





       void listbox1_SelectionChanged(object sender, SelectionChangedEventArgs e)
       {
           try
           {
               string dir = Environment.CurrentDirectory + @"\Files\MyFiles\";
               string file = listbox1.SelectedItem.ToString();

               System.Diagnostics.Process.Start(dir + file);
           }
           catch
           {
               MessageBox.Show("Error Loading File." + Environment.NewLine + "File Not Found.", "Error", MessageBoxButton.OK);

           }
       }



       void b_Click(object sender, RoutedEventArgs e)
       {
           string fileName = ((Button)sender).Tag.ToString();
           System.Diagnostics.Process.Start(fileName);
       }

       private void btnSave_Click(object sender, RoutedEventArgs e)
       {
           const string sPath = "save.txt";

           System.IO.StreamWriter SaveFile = new System.IO.StreamWriter(sPath);
           foreach (var item in listbox1.Items)
           {
               SaveFile.WriteLine(item);
           }

           SaveFile.Close();

           MessageBox.Show("Programs saved!");
       }