kursta yapmıstım bende buna dikkat et burada
bitane ClassSamle9
bide Form1.cs var(:

Form1.cs içindeki kos;

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace ClassSamle9
{
    public partial class Form1 : Form
    {
        Chart _chart = new Chart();
        public Form1()
        {
            InitializeComponent();
        }

        private void label3_Click(object sender, EventArgs e)
        {
 
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "")
            {
                MessageBox.Show("Ürün Adı Boş Bırakılamaz!", "Eksik alan", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                return;

            }
            if (textBox2.Text == "")
            {
                MessageBox.Show("Ürün Fiyatı Boş Bırakılamaz", "Eksik Alan", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                return;
            }
            if (textBox3.Text == "")
            {
                MessageBox.Show("Ürün Miktarı Boş Bırakılamaz", "Eksik Alan", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                return;
            }
            _chart.Add(textBox1.Text,int.Parse(textBox3.Text), decimal.Parse(textBox2.Text) );

            textBox4.Text = _chart.GrandTotal().ToString();

            listView1.Items.Clear();
            foreach (Product _p in _chart)
            {
                ListViewItem _li = new ListViewItem(_p.Name);
                _li.SubItems.Add(_p.Price.ToString());
                _li.SubItems.Add(_p.Amount.ToString());
                _li.SubItems.Add(_p.LineTotal().ToString());
                listView1.Items.Add(_li);
            }
                    

       }

        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Text = null;
            textBox2.Text = null;

            
        }
      
        private void button3_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }

        private void listView1_SelectedIndexChanged(object sender, EventArgs e)
        {

        }

        private void textBox2_TextChanged(object sender, EventArgs e)
        {

        }
        
    }
}

ClassSample9 içindeki kodlar bunlar işine yarayacagına eminim.

using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;

namespace ClassSamle9

 
   {    
    class Product
        
    {
        
        private string _name;

        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }

        private decimal _price;

        public decimal Price
        {
            get { return _price; }
            set { _price = value; }
        }
        private int _amount;

        public int Amount
        {
            get { return _amount; }
            set { _amount = value; }
        }

        public decimal LineTotal()
        {
            return _price * _amount;
        }
        public Product(string Name)
        {
            _name = Name;
        }
        public Product (string Name,int Amount,decimal Price)
        {
            _name=Name;
            _price=Price;
            _amount=Amount;
        }
    }

    class Chart :CollectionBase
    {
     public void Add (Product ProductIstance)
     {
     this.List.Add(ProductIstance);
     }

        public Product Add(string Name,int Amount,decimal Price)
        {
          Product _temp = new Product( Name,Amount,Price);
        this.List.Add(_temp);
        return _temp;
        }
        public decimal GrandTotal()
        {
        
        decimal _total = 0;
            foreach(Product _p in this.List)
                _total+=_p.LineTotal();
            return _total;
        }

    }
    
    }