Save GridView Column values to ViewState in ASP.Net

Here I have created sample that will help you out.

HTML

<div>
    <asp:GridView ID="gvDetails" runat="server" AutoGenerateColumns="true">
    </asp:GridView>
</div>
<asp:Button Text="Submit" runat="server" />

Code

protected void Page_Load(object sender, EventArgs e)
{
    if (ViewState["Ids"] != null)
    {
        gvDetails.DataSource = (List<int>)ViewState["Ids"];
        gvDetails.DataBind();
    }
    else
    {
        BindColumn();
    }
}

public void BindColumn()
{
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        List<int> Ids = new List<int>();
        using (SqlCommand cmd = new SqlCommand("SELECT CustomerId,Name FROM Customers", con))
        {
            con.Open();

            SqlDataReader sdr = cmd.ExecuteReader();

            while (sdr.Read())
            {
                Ids.Add(Convert.ToInt32(sdr["CustomerId"]));
            }
            con.Close();
            ViewState["Ids"] = Ids;
            gvDetails.DataSource = Ids;
            gvDetails.DataBind();
        }
    }
}

Screenshot