Insert Data into Parent and Child Tables from GridView using C# in ASP.Net

How to Inserting Data into Table from gridview after retrieving from database

I am retrieving data from database into gridview on Master Detail Form

Master Detail data is inserting into table, but Child data from gridview with multiple row are not getting inserting into table.

Here is my inserting query into table

protected void Save_Click(object sender, EventArgs e)
{
    if (txtRefno.Text == "")
    {
        Response.Write("<script language='javascript'>alert('Please Input Orderno Ref.');</script>");
    }
    else
    {
        using (SqlCommand cmd = new SqlCommand("[Sp_BalPakinsert]", con))
        {
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.AddWithValue("@Order_Ref_No", txtRefno.Text);
            cmd.Parameters.AddWithValue("@OrderNo", txtOrder.Text);
            con.Open();
            PID = Convert.ToInt32(cmd.ExecuteScalar());
            con.Close();
            DataTable dt = (DataTable)ViewState["dt"];
            int codeitem, qty, orderno, prdno;
            foreach (DataRow row in dt.Rows)
            {
                //pid = int.Parse(row["_PID"].ToString());
                prdno = int.Parse(row["Prdno"].ToString());
                orderno = int.Parse(row["Orderno"].ToString());
                qty = int.Parse(row["QTY"].ToString());
                codeitem = int.Parse(row["Codeitem"].ToString());
                this.InsertRows(codeitem, qty, orderno, prdno);
            }
        }
    }
}

private void InsertRows(int codeitem, int qty, int orderno, int prdno)
{
    con.Open();
    using (SqlCommand cmd = new SqlCommand("[SP_BalPakDetail_Insert]", con))
    {
        cmd.CommandType = CommandType.StoredProcedure;
        // cmd.Parameters.AddWithValue("@PDID", _PID);
        cmd.Parameters.AddWithValue("@PID", PID);
        cmd.Parameters.AddWithValue("@CodeItem", codeitem);
        cmd.Parameters.AddWithValue("@QTY", qty);
        cmd.Parameters.AddWithValue("@Orderno", orderno);
        cmd.Parameters.AddWithValue("@Prdno", prdno);
        cmd.ExecuteNonQuery();
        con.Close();
    }
}

public object PID { get; set; }    

Table structure 

 Master Table

CREATE TABLE [dbo].[tbl_BalPacM](
	[PID] [int] IDENTITY(1,1) NOT NULL,
	[OrderNo] [int] NULL,
	[Order_Ref_No] [varchar](50) NULL,
	[Date] [varchar](12) NULL,
 CONSTRAINT [PK_tbl_BalPacM] PRIMARY KEY CLUSTERED 
(
	[PID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

Child Table

CREATE TABLE [dbo].[tbl_PckDetail](
	[PDID] [int] IDENTITY(1,1) NOT NULL,
	[Prdno] [int] NULL,
	[Codeitem] [int] NULL,
	[OrderNo] [int] NULL,
	[QTY] [int] NULL,
	[PID] [int] NULL,
 CONSTRAINT [PK_tbl_PckDetail] PRIMARY KEY CLUSTERED 
(
	[PDID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]