GridView Export to Excel with dd/MM/yyyy date format in ASP.Net

You will need to create a new DataTable and save the date as string. Since if you export it as DateTime object, Excel will change is format as DateTime does not have any Format.

HTML

<asp:GridView ID="GridView1" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
    RowStyle-BackColor="#A1DCF2" AlternatingRowStyle-BackColor="White" AlternatingRowStyle-ForeColor="#000"
    runat="server" AutoGenerateColumns="false" AllowPaging="true" OnPageIndexChanging="OnPageIndexChanging">
    <Columns>
        <asp:BoundField DataField="ContactName" HeaderText="Contact Name" ItemStyle-Width="150px" />
        <asp:BoundField DataField="City" HeaderText="City" ItemStyle-Width="100px" />
        <asp:BoundField DataField="BirthDate" HeaderText="BirthDate" ItemStyle-Width="100px"
            DataFormatString="{0:dd/MM/yyyy}" />
    </Columns>
</asp:GridView>
<br />
<asp:Button ID="btnExport" runat="server" Text="Export To Excel" OnClick="ExportToExcel" />

Namespaces

using System.IO;
using System.Data;
using System.Drawing;
using System.Data.SqlClient;
using System.Configuration;

Code

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        this.BindGrid();
    }
}

private void BindGrid()
{
    DataTable dt = new DataTable();
    dt.Columns.AddRange(new DataColumn[3] { new DataColumn("ContactName", typeof(string)),
                    new DataColumn("City", typeof(string)),
                    new DataColumn("BirthDate",typeof(DateTime)) });
    dt.Rows.Add("Maria", "Boise", new DateTime(1990, 12, 14));
    dt.Rows.Add("Ana Trujillo", "Warszawa", new DateTime(1985, 9, 22));
    dt.Rows.Add("Antonio Moreno", "Mannheim", new DateTime(1991, 1, 17));
    dt.Rows.Add("Thomas Hardy", "Madrid", new DateTime(1987, 6, 5));
    GridView1.DataSource = dt;
    GridView1.DataBind();
    ViewState["Data"] = dt;
}

protected void OnPageIndexChanging(object sender, GridViewPageEventArgs e)
{
    GridView1.PageIndex = e.NewPageIndex;
    this.BindGrid();
}

protected void ExportToExcel(object sender, EventArgs e)
{
    Response.Clear();
    Response.Buffer = true;
    Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.xls");
    Response.Charset = "";
    Response.ContentType = "application/vnd.ms-excel";
    using (StringWriter sw = new StringWriter())
    {
        HtmlTextWriter hw = new HtmlTextWriter(sw);

        //To Export all pages
        GridView1.AllowPaging = false;
        DataTable dt = (DataTable)ViewState["Data"];
        DataTable dt2 = new DataTable();
        for (int i = 0; i < dt.Columns.Count; i++)
        {
            dt2.Columns.Add(dt.Columns[i].ColumnName, typeof(string));
        }
        for (int i = 0; i < dt.Rows.Count; i++)
        {
            dt2.ImportRow(dt.Rows[i]);
            dt2.Rows[i]["BirthDate"] = Convert.ToDateTime(dt2.Rows[i]["BirthDate"]).ToString("dd/MM/yyyy");
        }

        this.GridView1.DataSource = dt2;
        this.GridView1.DataBind();

        GridView1.HeaderRow.BackColor = Color.White;
        foreach (TableCell cell in GridView1.HeaderRow.Cells)
        {
            cell.BackColor = GridView1.HeaderStyle.BackColor;
        }
        foreach (GridViewRow row in GridView1.Rows)
        {
            row.BackColor = Color.White;
            foreach (TableCell cell in row.Cells)
            {
                if (row.RowIndex % 2 == 0)
                {
                    cell.BackColor = GridView1.AlternatingRowStyle.BackColor;
                }
                else
                {
                    cell.BackColor = GridView1.RowStyle.BackColor;
                }
                cell.CssClass = "textmode";
            }
        }

        GridView1.RenderControl(hw);

        //style to format numbers to string
        string style = @"<style> .textmode { mso-number-format:\@; } </style>";
        Response.Write(style);
        Response.Output.Write(sw.ToString());
        Response.Flush();
        Response.End();
    }
}

public override void VerifyRenderingInServerForm(Control control)
{
    /* Verifies that the control is rendered */
}

Screenshot