protected void LoaisachGridView_RowCommand(object sender, GridViewCommandEventArgs e)
    {
        if (e.CommandName == "xoa")
        {
            string maloai = (e.CommandArgument).ToString();
            loaisachBUS.XoaLoaiSach(maloai);
            NapDuLieu();
        }
        else if (e.CommandName == "sua")
        {
            
            LoaiSachCollection loaisachcoll = new LoaiSachCollection();
            
            
            loaisachcoll = loaisachBUS.TimDSLoaiSach(TimTextbox.Text);

            int index = Convert.ToInt32(e.CommandArgument.ToString());
            ViewState["MaLoai"] = loaisachcoll.Index(index).MaLoai;
            string tenloai = loaisachcoll.Index(index).TenLoai;
            SuaPopup.Show();
            SuaTextBox.Text = tenloai;
        }
    }
 public void NapLoaiSach()
 {
     LoaisachDropdown.Items.Clear();
     LoaiSachCollection source = new LoaiSachCollection();
     LoaiSachBO loaisachBO= new LoaiSachBO();
     loaisachBO.TenLoai = "Tất cả";
     loaisachBO.MaLoai = "";
     source.Add(loaisachBO);
     //add
     LoaiSachCollection temp = new LoaiSachCollection();
     temp = loaisachBUS.TimDSLoaiSach("");
     for (int i = 0; i < temp.Count; i++)
     {
         source.Add(temp.Index(i));
     }
     LoaisachDropdown.DataSource =source;
     LoaisachDropdown.DataTextField = "TenLoai";
     LoaisachDropdown.DataValueField = "Maloai";
     LoaisachDropdown.DataBind();
 }