将项目从数据库添加到组合框和文本框

Question

public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            listParent.Add("Chocolate");
            listParent.Add("Biscuit");
            listParent.Add("Milk");
            listParent.Add("Sugar");
            listParent.Add("Flour");
            listParent.Add("Ice Cream");

            listChild.Add(new Tuple<string, string>("Chocolate", "Kandos"));
            listChild.Add(new Tuple<string, string>("Chocolate", "Edna"));
            listChild.Add(new Tuple<string, string>("Chocolate", "Mars"));
            listChild.Add(new Tuple<string, string>("Chocolate", "Rovello"));

            listChild.Add(new Tuple<string, string>("Biscuit", "Maliban"));
            listChild.Add(new Tuple<string, string>("Biscuit", "Munchee"));
            listChild.Add(new Tuple<string, string>("Biscuit", "Maam"));

            listChild.Add(new Tuple<string, string>("Milk", "Anchor"));
            listChild.Add(new Tuple<string, string>("Milk", "Nespray"));
            listChild.Add(new Tuple<string, string>("Milk", "Raththi"));
            listChild.Add(new Tuple<string, string>("Milk", "Lakspray"));

            listChild.Add(new Tuple<string, string>("Sugar", "Arpico"));
            listChild.Add(new Tuple<string, string>("Sugar", "Cargils"));

            listChild.Add(new Tuple<string, string>("Flour", "Prima"));
            listChild.Add(new Tuple<string, string>("Flour", "MDK"));

            listChild.Add(new Tuple<string, string>("Ice Cream", "Elephant House"));
            listChild.Add(new Tuple<string, string>("Ice Cream", "Keels"));
            listChild.Add(new Tuple<string, string>("Ice Cream", "Highland"));



            foreach (var item in listParent)
            {
                cmbParent.Items.Add(item);
            }
        }

        List<String> listParent = new List<String>();
        List<Tuple<String, String>> listChild = new List<Tuple<String, String>>();

In my c# program I have two combo boxes. One combo box changes its value according to the first combo box. The first combo box shows " product category " & the second one shows " product brand " according to the first one. I have already written the code that does this correctly.

Now I have entered all the " product brands " with their " prices " in to a database. I want to add a text box that shows the price of the currently selected product from the second combo box. In other words, when the value of the second combo box changes the price textbox should also change.

If I have entered the price of chocolate in database as $100 when I choose chocolate from combo box, the text box value should be 100.

Help me to write the code. I am new to c#.

Answer 1

you have to add event handler to your comboboxes.

Add SelectedItemChanged event hander to your cmbParent combobox, so when user changes product category, you can filter listChild and remove other product categories. Then, add those filtered items to your other combo ( cmbChild ).

Next thing is to add SelectedItemChanged event hander to your cmbChild combobox. When user selects something from that combo, event will fire and you can connect to database and fetch prices.

Take a look at code that implements said things.

        public Form1()
        {
            InitializeComponent();


            listParent.Add("Chocolate");
            listParent.Add("Biscuit");
            listParent.Add("Milk");
            listParent.Add("Sugar");
            listParent.Add("Flour");
            listParent.Add("Ice Cream");

            listChild.Add(new Tuple<string, string>("Chocolate", "Kandos"));
            listChild.Add(new Tuple<string, string>("Chocolate", "Edna"));
            listChild.Add(new Tuple<string, string>("Chocolate", "Mars"));
            listChild.Add(new Tuple<string, string>("Chocolate", "Rovello"));

            listChild.Add(new Tuple<string, string>("Biscuit", "Maliban"));
            listChild.Add(new Tuple<string, string>("Biscuit", "Munchee"));
            listChild.Add(new Tuple<string, string>("Biscuit", "Maam"));

            listChild.Add(new Tuple<string, string>("Milk", "Anchor"));
            listChild.Add(new Tuple<string, string>("Milk", "Nespray"));
            listChild.Add(new Tuple<string, string>("Milk", "Raththi"));
            listChild.Add(new Tuple<string, string>("Milk", "Lakspray"));

            listChild.Add(new Tuple<string, string>("Sugar", "Arpico"));
            listChild.Add(new Tuple<string, string>("Sugar", "Cargils"));

            listChild.Add(new Tuple<string, string>("Flour", "Prima"));
            listChild.Add(new Tuple<string, string>("Flour", "MDK"));

            listChild.Add(new Tuple<string, string>("Ice Cream", "Elephant House"));
            listChild.Add(new Tuple<string, string>("Ice Cream", "Keels"));
            listChild.Add(new Tuple<string, string>("Ice Cream", "Highland"));



            foreach (var item in listParent)
            {
                cmbParent.Items.Add(item);
            }

            cmbParent.SelectedIndexChanged += CmbParent_SelectedIndexChanged;
            cmbChild.SelectedIndexChanged += CmbChild_SelectedIndexChanged;
        }

        List<String> listParent = new List<String>();
        List<Tuple<String, String>> listChild = new List<Tuple<String, String>>();


        private void CmbChild_SelectedIndexChanged(object sender, EventArgs e)
        {
            string selectedBrand = (string)cmbChild.SelectedItem;

            //get data from database
            SqlConnection conn = new SqlConnection("[your connection string]");
            SqlCommand command = new SqlCommand();
            command.Connection = conn;

            command.CommandText = "Select Price from [your table] where productBrand = @productBrand";
            command.Parameters.AddWithValue("@productBrand", selectedBrand);

            conn.Open();
            decimal price = (decimal)command.ExecuteScalar();

            txtPrice.Text = price.ToString();

            conn.Close();
        }

        private void CmbParent_SelectedIndexChanged(object sender, EventArgs e)
        {
            List<Tuple<String, String>> productsList = new List<Tuple<String, String>>();
            productsList = listChild.Where(x => x.Item1 == (string)cmbParent.SelectedItem).ToList();

            cmbChild.Items.Clear();
            foreach (var item in productsList)
            {
                cmbChild.Items.Add(item.Item2);
            };
        }