Export to CSV Website asp - asp.net

Question

I have a GridView and when I click Export Button to export my data into CSV. I click the button and it takes all the data correctly but it doesn't show anything, no popup to ask me to open or to save .
Here is my code
protected void btnExport_Click(object sender, EventArgs e)
{
ExportCSV();
}
protected void ExportCSV()
{
GridViewSW.DataSource = ViewState["source"];
Response.Clear();
Response.Buffer = true;
Response.AddHeader("content-disposition", "attachment;filename=Orders.csv");
Response.Charset = "";
Response.ContentType = "application/text";
GridViewSW.AllowPaging = false;
GridViewSW.DataBind();
StringBuilder columnbind = new StringBuilder();
for (int k = 0; k < GridViewSW.Columns.Count; k++)
{
columnbind.Append(GridViewSW.Columns[k].HeaderText + ",");
}
columnbind.Append("\r\n");
for (int i = 0; i < GridViewSW.Rows.Count; i++)
{
for (int j = 0; j < GridViewSW.Columns.Count; j++)
{
columnbind.Append(GridViewSW.Rows[i].Cells[j].Text + ",");
}
columnbind.Append("\r\n");
}
Response.Output.Write(columnbind.ToString());
Response.Flush();
Response.End();
}
NEW EDIT
I changed the code a little bit. Now i have the csv file and he has all the data in, but when I click the button it doesn't show any dialog box with open or save.
string fullSavePath = HttpContext.Current.Server.MapPath(string.Format("~/csv/Orders.csv"));
StreamWriter sr = new StreamWriter(fullSavePath);
DataSet ds = (DataSet)ViewState["source"];
MyDateTime date = new MyDateTime();
DataTableReader dr = ds.Tables[0].CreateDataReader();
while (dr.Read())
{
sr.Write(dr.GetValue(0) + "," + date.ConvertToDate(Convert.ToInt64(dr.GetValue(2))) + "," + date.ConvertToDate(Convert.ToInt64(dr.GetValue(3))) + "," + dr.GetValue(4) + "\r\n");
}
sr.Flush();
sr.Close();
sr.Dispose();
System.IO.FileInfo file = new System.IO.FileInfo(fullSavePath);
System.Web.HttpContext context = System.Web.HttpContext.Current;
System.Web.HttpResponse response = context.Response;
Response.Clear();
Response.ClearHeaders();
Response.ClearContent();
Response.AddHeader("Content-Length", file.Length.ToString());
Response.ContentType = "text/csv";
Response.AddHeader("Content-Disposition", string.Format("attachment; filename =" + "Orders.csv"));
// Response.TransmitFile(fullSavePath);
Response.WriteFile(file.FullName);
// Response.Flush();
context.ApplicationInstance.CompleteRequest();
// Response.End();
// Response.Close();

Answer 1

I believe you need to change your content type to "text/csv"
Response.ContentType = "text/csv";