private void bt_moi_Click(object sender, EventArgs e)
{
resettext();
Enable(true);
cb_loaiNV.Refresh();
cb_loaiNV.SelectedIndex = 2;
tbl_NhanVien.ClearSelection();
NhanVienBus nvBus = new NhanVienBus();
txt_manv.Text = (nvBus.MaNVNow() + 1).ToString();
txt_manv.Enabled = false;
txt_ngayLam.Value = DateTime.Now;
txt_ngaysinh.Value = DateTime.Parse("12/31/1996");
cb_loaiNV.Focus();
bt_them.Visible = true;
bt_Luu.Visible = false;
txt_pass.ReadOnly = true;
txt_user.ReadOnly = false;
visiable_user(false);
visiable_pass(false);
}