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();
}