using System;
using System.IO;
using System.Web;
using System.Runtime.InteropServices;
using System.Web.UI;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Serialization;
using System.Web.UI.WebControls;

using Microsoft.SharePoint;
using Microsoft.SharePoint.WebControls;
using Microsoft.SharePoint.WebPartPages;

namespace ExportGridtoExcel
{
    [Guid("2fa65763-1ef1-4173-8a77-685e840f0196")]
    public class ExportGridtoExcel : System.Web.UI.WebControls.WebParts.WebPart
    {
        SPGridView myGridView;
        SPDataSource myDataSource = new SPDataSource();
        Button oBtn_Export;

        protected override void CreateChildControls()
        {
            oBtn_Export = new Button();
            oBtn_Export.Text = "Export to Excel";
            oBtn_Export.CssClass = "ButtonHeightWidth";
            oBtn_Export.Click += new EventHandler(oBtn_Export_Click);
            this.Controls.Add(oBtn_Export);

            myGridView = new SPGridView();
            myGridView.Enabled = true;
            myGridView.AutoGenerateColumns = false;                       

            SPBoundField colTitle = new SPBoundField();
            colTitle.DataField = "Country";
            colTitle.HeaderText = "Country";
            this.myGridView.Columns.Add(colTitle);

            SPBoundField colMission = new SPBoundField();
            colMission.DataField = "State";
            colMission.HeaderText = "State";
            this.myGridView.Columns.Add(colMission);

            this.Controls.Add(myGridView);
        }

        void oBtn_Export_Click(object sender, EventArgs e)
        {
            ExportToExcel("CountryState.xls", myGridView);
        }

        protected override void OnPreRender(EventArgs e)
        {
            base.OnPreRender(e);
            SPSite mySite = SPContext.Current.Site;
            SPWeb myWeb = SPContext.Current.Web;
            SPList list = myWeb.Lists["Countries"];
            myDataSource.List = list;
            myGridView.DataSource = myDataSource;
            myGridView.DataBind();           
        }

        public static void ExportToExcel(string strFileName, SPGridView gv)
        {
            using (StringWriter sw = new StringWriter())
            {
                using (HtmlTextWriter htw = new HtmlTextWriter(sw))
                {
                    //  Create a form to contain the grid
                    Table table = new Table();

                    //  add the header row to the table
                    if (gv.HeaderRow != null)
                    {
                        PrepareControlForExport(gv.HeaderRow);
                        table.Rows.Add(gv.HeaderRow);
                    }

                    //  add each of the data rows to the table
                    foreach (GridViewRow row in gv.Rows)
                    {
                        PrepareControlForExport(row);
                        table.Rows.Add(row);
                    }

                    //  add the footer row to the table
                    if (gv.FooterRow != null)
                    {
                        PrepareControlForExport(gv.FooterRow);
                        table.Rows.Add(gv.FooterRow);
                    }

                    //  render the table into the htmlwriter
                    table.RenderControl(htw);

                    HttpContext.Current.Response.Clear();
                    HttpContext.Current.Response.AddHeader("content-disposition", string.Format("attachment; filename={0}", strFileName));
                    HttpContext.Current.Response.ContentType = "application/ms-excel";
                    HttpContext.Current.Response.Cache.SetCacheability(HttpCacheability.NoCache);
                    //render the htmlwriter into the response
                    HttpContext.Current.Response.Write(sw.ToString());
                    HttpContext.Current.Response.End();
                }
            }
        }

        private static void PrepareControlForExport(Control control)
        {
            for (int i = 0; i < control.Controls.Count; i++)
            {
                Control current = control.Controls[i];
                if (current is LinkButton)
                {
                    control.Controls.Remove(current);
                    control.Controls.AddAt(i, new LiteralControl((current as LinkButton).Text));
                }
                else if (current is ImageButton)
                {
                    control.Controls.Remove(current);
                    control.Controls.AddAt(i, new LiteralControl((current as ImageButton).AlternateText));
                }
                else if (current is HyperLink)
                {
                    control.Controls.Remove(current);
                    control.Controls.AddAt(i, new LiteralControl((current as HyperLink).Text));
                }
                else if (current is DropDownList)
                {
                    control.Controls.Remove(current);
                    control.Controls.AddAt(i, new LiteralControl((current as DropDownList).SelectedItem.Text));
                }
                else if (current is CheckBox)
                {
                    control.Controls.Remove(current);
                    control.Controls.AddAt(i, new LiteralControl((current as CheckBox).Checked ? "True" : "False"));
                }

                if (current.HasControls())
                {
                    PrepareControlForExport(current);
                }
            }
        }
    }
}