Hướng dẫn xây dựng trang mua hàng đơn giản

    protected void DataList1_ItemCommand(object source, DataListCommandEventArgs e)
    {
        int sd = e.Item.ItemIndex;
        
        DataTable tb = new DataTable();
        string name = e.CommandName;
        if (name == "add")
        {
            string ma = DataList1.DataKeys[sd].ToString();

            Label ten = (Label)e.Item.FindControl("lbltenhang");
            string t = ten.Text;

            Label gia= (Label)e.Item.FindControl("lblgia");
            int giasp = int.Parse(gia.Text);

            tb=ThemGioHang(t, giasp, 1, ma);
        }

        Session["GioHang"] = tb;
        Response.Redirect("giohang.aspx");
    }

     public DataTable tb = new DataTable();
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            tb = (DataTable)Session["GioHang"];
            if (tb != null)
            {
                if (tb.Rows.Count > 0)
                {
                    GridView1.DataSource = tb;
                    GridView1.DataBind();
                }
                lbltongtien.Text = tongtien(tb).ToString();
            }
        }
    }

  protected void ImageButton1_Click(object sender, ImageClickEventArgs e)
    {
        tb = (DataTable)Session["GioHang"];
        for (int i = 0; i < GridView1.Rows.Count; i++)
        {
           TextBox sl = (TextBox)GridView1.Rows[i].FindControl("txtsl");
           int soluong = int.Parse(sl.Text);
            //cập nhật số lượng cho giỏ hàng
           tb.Rows[i]["SoLuong"] = soluong;
            //lấy đơn giá của hàng từ giỏ hàng về. 
           int g = int.Parse(tb.Rows[i]["gia"].ToString());
            //cập nhật tổng giá cho giỏ hàng.
           tb.Rows[i]["TongGia"] = g * soluong;
        }
        //load dữ liệu lại cho Gridview
        GridView1.DataSource = tb;
        GridView1.DataBind();
        //hiển thị tổng tiền.
        lbltongtien.Text = tongtien(tb).ToString();
    }

public float tongtien(DataTable tb)
    {
        float tt = 0;
        for (int i = 0; i < tb.Rows.Count; i++)
        {
            tt=tt + float.Parse(tb.Rows[i]["TongGia"].ToString());
        }
        return tt;
    }

using System;
using System.Data;
using System.Configuration;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;

/// <summary>
/// Summary description for Giohang
/// </summary>
public class Giohang
{
    //Lam thu gio hang voi datatable
    DataTable tb = new DataTable();

    public Giohang()
    {
        //if (tb.Columns == null)
        {
            tb.Columns.Add("AnhSP");
            tb.Columns.Add("TenSP");
            tb.Columns.Add("SoLuong");
            tb.Columns.Add("Gia");
            tb.Columns.Add("TongGia");
            tb.Columns.Add("MaSP");
            tb.Columns.Add("MaNhanHieu");
        }
    }

    public DataTable getTable()
    {
        return this.tb;
    }

    public void setTable(DataTable tb)
    {
        this.tb = tb;                
    }
    //phuong thuc them 1 san pham moi vao gioi hang
    public DataTable addToShoppingCart(string maNhanHieu, string tenSP, string maSP, string anhSP, double soLuong, double gia)
    {
        bool kiemTra = false;
        if (tb.Rows.Count != 0)
        {
            foreach (DataRow dr in tb.Rows)
            {
                if (dr[1].ToString().Equals(tenSP))
                {                    
                    dr[2] = double.Parse(dr[2].ToString()) + 1;
                    dr[3] = gia;
                    dr[4] = (double.Parse(dr[2].ToString())*gia).ToString();
                    dr[5] = maSP;
                    dr[6] = maNhanHieu;
                    kiemTra = true;
                }               
            }
            if (!kiemTra)
            {
                DataRow row = tb.NewRow();
                row[0] = anhSP;
                row[1] = tenSP;
                row[2] = soLuong;
                row[3] = gia.ToString();
                row[4] = gia * soLuong;
                row[5] = maSP;
                row[6] = maNhanHieu;
                tb.Rows.Add(row);
            }
        }
        else
        {
            DataRow row = tb.NewRow();
            row[0] = anhSP;
            row[1] = tenSP;
            row[2] = soLuong;
            row[3] = gia.ToString();
            row[4] = gia * soLuong;
            row[5] = maSP;
            row[6] = maNhanHieu;
            tb.Rows.Add(row);
        }
        return tb;
    }

    public DataTable delete(DataTable datatable, string maSP)
    {
        DataTable tb = datatable;
        foreach (DataRow row in tb.Rows)
        {
            if (maSP.Equals(row[5].ToString()))
            {
                tb.Rows.Remove(row);
                break;
            }
        }
        return tb;
    }

    public DataTable upDate(DataTable datatable, double soLuong, string maSP)
    {
        DataTable tb = datatable;
        foreach (DataRow row in tb.Rows)
        {
            if(maSP.Equals(row[5].ToString()))
            {
                row[2] = soLuong;
                row[4] = double.Parse(row[3].ToString()) * soLuong;
            }
        }
        return tb;
    }

}