How to read from existing excel sheet and how to create new excel sheet and write to that?

Hi Karthik,


using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;
using System.IO;
namespace Retrieving_excel_data_to_combobox_exportxls
{
    public partial class Form1 : Form
    {
        public OleDbConnection con;
        public void pintu(string s)
        {
            con = new OleDbConnection("provider=Microsoft.Jet.OLEDB.4.0; " + "data source='" + s + " '; " + "Extended Properties=Excel 8.0;");

        }
        public OleDbCommand com;
        public DataSet ds;
        public OleDbDataAdapter oledbda;
        public DataTable dt;
        public string str;
        public Form1()
        {
            InitializeComponent();
        }

        private void btnbrowse_Click(object sender, EventArgs e)
        {
            OpenFileDialog openfiledialog1 = new OpenFileDialog();
            openfiledialog1.ShowDialog();
            openfiledialog1.Filter = "allfiles|*.xls";
            TextBox1.Text = openfiledialog1.FileName;
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            comboBox1.Text = "Please select";
        }

        private void btndisplay_Click(object sender, EventArgs e)
        {
            pintu(TextBox1.Text);
            try
            {
                con.Open();
                str = "select * from [sheet1$]";
                com = new OleDbCommand(str, con);
                ds = new DataSet();
                oledbda = new OleDbDataAdapter(com);
                oledbda.Fill(ds, "[sheet1$]");
                con.Close();
                DataGridView1.DataSource = ds;
                DataGridView1.DataMember = "[sheet1$]";
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }


            try
            {
                con.Open();
                str = "select * from [sheet1$]";
                com = new OleDbCommand(str, con);
                oledbda = new OleDbDataAdapter(com);
                ds = new DataSet();
                oledbda.Fill(ds, "[sheet1$]");
                con.Close();

                dt = ds.Tables["[sheet1$]"];
                int i = 0;
                for (i = 0; i <= dt.Rows.Count - 1; i++)
                {
                    comboBox1.Items.Add(dt.Rows[i].ItemArray[0]);
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

        }

        private void btn_export_Click(object sender, EventArgs e)
        {
            //We have to add a reference to the Microsoft Excel object library.
            //Right click on your project and select Add Reference menu. After that go to COM tab and select and add Microsoft Excel 12.0 object library.

            Microsoft.Office.Interop.Excel._Application app = new Microsoft.Office.Interop.Excel.Application();
            Microsoft.Office.Interop.Excel._Workbook workbook = app.Workbooks.Add(Type.Missing);
            Microsoft.Office.Interop.Excel._Worksheet worksheet = null;
            app.Visible = true;

            try
            {

                worksheet = (Microsoft.Office.Interop.Excel.Worksheet)workbook.Sheets["Sheet1"];
                worksheet = (Microsoft.Office.Interop.Excel.Worksheet)workbook.ActiveSheet;
                worksheet.Name = "Exported from DataGridView";

                for (int i = 1; i < DataGridView1.Columns.Count + 1; i++)
                {
                    worksheet.Cells[1, i] = DataGridView1.Columns[i - 1].HeaderText;
                }

                for (int i = 0; i < DataGridView1.Rows.Count - 1; i++)
                {
                    for (int j = 0; j < DataGridView1.Columns.Count; j++)
                    {
                        worksheet.Cells[i + 2, j + 1] = DataGridView1.Rows[i].Cells[j].Value.ToString();
                    }
                }


                string fileName = String.Empty;

                saveFileExcel.Filter = "Excel files |*.xls|All files (*.*)|*.*";
                saveFileExcel.FilterIndex = 2;
                saveFileExcel.RestoreDirectory = true;

                if (saveFileExcel.ShowDialog() == DialogResult.OK)
                {
                    fileName = saveFileExcel.FileName;

                    workbook.SaveAs(fileName, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Microsoft.Office.Interop.Excel.XlSaveAsAccessMode.xlExclusive, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing);

                }
                else
                    return;

            }
            catch (System.Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            finally
            {
                app.Quit();
                workbook = null;
                app = null;
            }
        }
    }
}


Thanks