Grid view sorting and paging after performing search

Question

I am performing a search operation in GridView and getting results as expected, but after getting results, if I sort them or click on pagination, the page getting reloaded and sorting and pagination happening for the whole grid. I want sorting and paging should only work for search results which I have got.

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

protected void bindgrid()
{
ViewState["sortexp"] = "";
ViewState["orderby"] = "ASC";
Sort("");
int iTotalRecords = ((DataTable)(GridView1.DataSource)).Rows.Count;
lbldisplay.Text = "Total Products: " + iTotalRecords.ToString();
}

protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
GridView1.PageIndex = e.NewPageIndex;
GridView1.DataBind();
bindgrid();
}
public void Sort(string sortexp)
{
DataTable dt = (DataTable)bll.LoadProduct();
DataView DV = dt.DefaultView;if (sortexp != "")
{
DV.Sort = sortexp;
}
GridView1.DataSource = DV;
GridView1.DataBind();
}
protected void GridView1_Sorting(object sender, GridViewSortEventArgs e)
{
if (ViewState["orderby"].ToString() == "ASC")
{
ViewState["orderby"] = "DESC";
ViewState["sortexp"] = e.SortExpression + " " + " DESC";
}else
{
ViewState["orderby"] = "ASC";
ViewState["sortexp"] = e.SortExpression + " " + " ASC";
}
Sort(ViewState["sortexp"].ToString());
}