private void simpleButton6_Click(object sender, EventArgs e)
        {
            ThongtinKH f = new ThongtinKH(this, null, null);

            //txtmakh.Text = MaKH;
            f.Show();
        }
        private void simpleButton6_Click(object sender, EventArgs e)
        {
            ThongtinKH f = new ThongtinKH(null, null, this);

            f.Show();
        }