private void btnThem_Click(object sender, EventArgs e)
{
TaiLieu tl = new TaiLieu();
panel3.Visible = true;
panel1.Width = 803;
panel1.Height = 659;
pictureBox1.Image = null;
pictureBox2.Image = null;
txtNgayNhap.Text = (DateTime.Now).ToString();
cbbMaChiTiet.Enabled = false;
cbbMaChiTiet.Text = (int.Parse(tl.taoMaTuDong()) + 1).ToString();
cbbMaTaiLieu.Enabled = false;
cbbMaTaiLieu.Text = matailieu;
cbbNhaCC.Enabled = true;
cbbNhaXB.Enabled = true;
cbbSoLuong.Enabled = true;
cbbTacGia.Enabled = true;
cbbTenChiTiet.Enabled = true;
cbbViTri.Enabled = true;
txtGiaBia.Enabled = true;
txtGiaNhap.Enabled = true;
txtLink.Enabled = true;
txtNguoiNhap.Enabled = true;
txtSoTrang.Enabled = true;
// xoa trang
cbbNhaCC.Text = "";
cbbNhaXB.Text = "";
cbbSoLuong.Text = "";
cbbTacGia.Text = "";
cbbTenChiTiet.Text = "";
cbbViTri.Text = "";
txtGiaBia.Text = "";
txtGiaNhap.Text = "";
txtLink.Text = "";
txtNguoiNhap.Text = "";
txtSoTrang.Text = "";
cbbTenChiTiet.Focus();
themhaysua = "them";
}