[Solved] ASP.Net Error: Cannot insert the value NULL into column CustomerId

Hi sir,

I have write above code but it show error when I Click on insert button.

The error is

An exception of type 'System.Data.SqlClient.SqlException' occurred in System.Data.dll but was not handled in user code

Additional information: Cannot insert the value NULL into column 'CustomerId', table

I want that when I input data then there should be automatically generate id with bar code and save into database and all data with barcode id should goes to next page for print.

Sir I am really helpless by doing this.

namespace Dispatchwebform
{
    public partial class defaultpage : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!this.IsPostBack)
            {
                this.BindGrid();
            }
        }

        protected void Send(object sender, EventArgs e)
        {
            GridViewRow gvRow = (sender as LinkButton).NamingContainer as GridViewRow;
            Response.Redirect("print.aspx?Id=" + gvRow.Cells[0].Text);
        }

        protected void Insert(object sender, EventArgs e)
        {
            string name = txtName.Text;
            string country = txtCountry.Text;
            txtName.Text = "";
            txtCountry.Text = "";
            string constring = ConfigurationManager.ConnectionStrings["dbcs"].ConnectionString;
            using (SqlConnection con = new SqlConnection(constring))
            {
                using (SqlCommand cmd = new SqlCommand("Insert into Customers (Name, Country) Values(@Name, @Country)", con))
                {
                    cmd.CommandType = CommandType.Text;
                    cmd.Parameters.AddWithValue("@Name", name);
                    cmd.Parameters.AddWithValue("@Country", country);
                    con.Open();
                    cmd.ExecuteNonQuery();
                    con.Close();
                }
            }
            this.BindGrid();
        }
        private void BindGrid()
        {
            string conString = ConfigurationManager.ConnectionStrings["dbcs"].ConnectionString;
            using (SqlConnection con = new SqlConnection(conString))
            {
                using (SqlCommand cmd = new SqlCommand("SELECT * FROM Customers", con))
                {
                    cmd.CommandType = CommandType.Text;
                    con.Open();
                    this.gvCustomers.DataSource = cmd.ExecuteReader();
                    this.gvCustomers.DataBind();
                    con.Close();
                }
            }
        }
    }
}

namespace Dispatchwebform
{
    public partial class print : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!this.IsPostBack)
            {
                string conString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
                using (SqlConnection con = new SqlConnection(conString))
                {
                    using (SqlCommand cmd = new SqlCommand("Select * From Customers WHERE CustomerId = @Id", con))
                    {
                        cmd.CommandType = CommandType.Text;
                        cmd.Parameters.AddWithValue("@Id", Request.QueryString["Id"]);
                        con.Open();
                        SqlDataReader sdr = cmd.ExecuteReader();
                        if (sdr.Read())
                        {
                            lblName.Text = sdr["Name"].ToString();
                            lblCountry.Text = sdr["Country"].ToString();
                            imgBarCode.ImageUrl = "data:image/png;base64," + Convert.ToBase64String(GenerateBarcode(sdr["CustomerId"].ToString()) as byte[]);
                        }
                        con.Close();
                    }
                }
            }

        }
        protected byte[] GenerateBarcode(string id)
        {
            byte[] byteImage;
            using (Bitmap bitMap = new Bitmap(id.Length * 40, 80))
            {
                using (Graphics graphics = Graphics.FromImage(bitMap))
                {
                    Font oFont = new Font("IDAutomationHC39M Free Version", 16);
                    PointF point = new PointF(2f, 2f);
                    SolidBrush blackBrush = new SolidBrush(Color.Black);
                    SolidBrush whiteBrush = new SolidBrush(Color.White);
                    graphics.FillRectangle(whiteBrush, 0, 0, bitMap.Width, bitMap.Height);
                    graphics.DrawString("*" + id + "*", oFont, blackBrush, point);
                }
                using (MemoryStream ms = new MemoryStream())
                {
                    bitMap.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
                    byteImage = ms.ToArray();
                }
            }

            return byteImage;
        }
    }
}