private void btnThemmoi_Click(object sender, EventArgs e)
        {
            int dem = 0;

            if (this.txtMaDeTai.Text.Trim().Length <= 0)
            {
                this.errorProvider1.SetError(this.txtMaDeTai, "Phai nhap ma de tai");
                dem++;
            }
            else
            {
                this.errorProvider1.SetError(this.txtMaDeTai, null);
            }
            if (this.txtTenDT.Text.Trim().Length <= 0)
            {
                this.errorProvider2.SetError(this.txtTenDT, "Phai nhap ten de tai");
                dem++;
            }
            else
            {
                this.errorProvider2.SetError(this.txtTenDT, null);
            }
            if (this.cboNhom.Text.Trim().Length <= 0)
            {
                this.errorProvider3.SetError(this.cboNhom, "Phai chon nhom");
                dem++;
            }
            else
            {
                this.errorProvider4.SetError(this.cboNhom, null);
            }
            if (this.cboLoaiDeTai.Text.Trim().Length <= 0)
            {
                this.errorProvider4.SetError(this.cboLoaiDeTai, "Phai chon loai de tai");
                dem++;
            }
            else
            {
                this.errorProvider4.SetError(this.cboLoaiDeTai, null);
            }
            if (this.cboGiaoVien.Text.Trim().Length <= 0)
            {
                this.errorProvider5.SetError(this.cboGiaoVien, "Phai nhap giao vien huong dan");
                dem++;
            }
            else
            {
                this.errorProvider5.SetError(this.cboGiaoVien, null);
            }
            if (dem != 0)
            {
                return;
            }
            DeTai dt = new DeTai();

            dt.MaDT    = this.txtMaDeTai.Text.Trim();
            dt.TenDT   = this.txtTenDT.Text.Trim();
            dt.LoaiDT  = this.cboLoaiDeTai.Text.Trim();
            dt.MaNhom  = this.cboNhom.Text.Trim();
            dt.MaGV    = this.cboGiaoVien.Text.Trim();
            dt.NoiDung = this.txtNoiDung.Text.Trim();

            if (DeTaiController.AddDT(dt) == false)
            {
                MessageBox.Show("Mã đề tài bị trùng");
                return;
            }
            DeTaiController.AddDT(dt);
            BindingSource source = new BindingSource();

            source.DataSource             = DeTaiController.getListDT();
            this.dataGridView1.DataSource = source;
        }