private void Refresh_MouseUp(object sender, MouseButtonEventArgs e)
 {
     MaVach.Text     = "";
     TenSanPham.Text = "";
     GiaTien.Text    = "";
     MaVach.Focus();
     MaVach.SelectAll();
 }
 private void InputMaVach_MouseDown(object sender, MouseButtonEventArgs e)
 {
     MaVach.Focus();
     MaVach.SelectAll();
 }