private void btOK_Click(object sender, System.EventArgs e)
 {
     if (listBox1.SelectedIndex >= 0)
     {
         Type tp = (Type)listBox1.Items[listBox1.SelectedIndex];
         objRet = (DrawingItem)Activator.CreateInstance(tp);
         objRet.ResetDefaultProperties();
         Close();
     }
 }