ASP.NET

@model MyProject.Models.Product

@using (Html.BeginForm())
{
    <div>
        @Html.LabelFor(m => p.Name, "Name:")
        @Html.TextBoxFor(m => p.Name)
    </div>
    <input type="submit" value="Create" />
}

@model MyProject.Models.Product
@addtaghelper "Microsoft.AspNet.Mvc.TagHelpers"

<form asp-controller="Products" asp-action="Create" method="post">
    <div>
        <label asp-for="Name">Name:</label>
        <input asp-for="Name" />
    </div>

    <input type="submit" value="Save" />
</form>

public override void VerifyRenderingInServerForm(Control control)
{
}
protected void btnCSV_Click(object sender, ImageClickEventArgs e)
{
Response.Content="";
Response.AddHeader("content-disposition", string.Format("attachment; filename={0}", "attachment.csv"));
Response.ContentType = "application/text";(also tried vnd.csv)
gv1.AllowPaging = false;
gv1.DataBind();
StringBuilder sb = new StringBuilder();
for (int i = 0; i < gv1.Columns.Count; i++)
{

sb.Append(gv1.Columns[i].HeaderText + ',');
}

sb.Append("\n");
for (int j = 0; j < gv1.Rows.Count; j++)
{
for (int k = 0; k < gv1.Columns.Count; k++)
{

sb.Append(gv1.Rows[j].Cells[k].Text + ',');
}

sb.Append("\n");
}
Response.Write(sb.ToString());
Response.End();
}