combo box to datagrid view..didn't get items in grid view

Question

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Text;

using System.Windows.Forms;

namespace Practice1

{

public partial class Form4 : Form

{

DataTable resultDT = new DataTable();

public Form4()

{

InitializeComponent();

}

private void Form4_Load(object sender, EventArgs e)

{

Emp objEmp = new Emp();

DataTable dttt = objEmp.getItem();

cbItems.DataSource = dttt;

cbItems.ValueMember = "ItemId";

cbItems.DisplayMember = "ItemName";

}

public DataTable getResult()

{

resultDT.Columns.Add("ItemId");

resultDT.Columns.Add("ItemName");

resultDT.Columns.Add("Quantity");

resultDT.Columns.Add("rate");

resultDT.Columns.Add("total cost");

resultDT.Columns.Add("MRP");

resultDT.Columns.Add("tax");

resultDT.Columns.Add("per unit cost");

resultDT.Columns.Add("Net amount");

DataRow rowDR = resultDT.NewRow();

rowDR["ItemId"] = cbItems.SelectedValue;

rowDR["ItemName"] = cbItems.Text;

rowDR["Quantity"] = txtQuantity.Text;

rowDR["rate"] = txtRate.Text;

rowDR["total cost"] = Convert.ToInt32(txtQuantity.Text) * Convert.ToInt32(txtRate.Text);

double cost = Convert.ToInt32(txtQuantity.Text) * Convert.ToInt32(txtRate.Text);

double tax = (cost * Convert.ToInt32(txttax.Text) / 100);

double totaltax = cost + tax;

double totaltaxx = totaltax / Convert.ToInt32(txtQuantity.Text);

rowDR["per unit cost"] = totaltaxx;

rowDR["Net amount"] = Convert.ToInt32(txtQuantity.Text) * totaltaxx;

rowDR["MRP"] = txtMRP.Text;

rowDR["tax"] = txttax.Text;

resultDT.Rows.Add(rowDR);

return resultDT;

}

private void button1_Click(object sender, EventArgs e)

DataTable resultDT = getResult();

dataGridView1.DataSource = resultDT;

}

}

}