Sort and page the results

public SortDirection SortDir
    {
        get
        {
            if (ViewState["sortDirection"] == null)
            {
                ViewState["sortDirection"] = SortDirection.Ascending;
            } return (SortDirection)ViewState["sortDirection"];
        }
        set
        {
            ViewState["sortDirection"] = value;
        }
    }

    DataSet ds = new DataSet();
    DataView dv = new DataView();

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            BindGrid();
            GridView1.DataSource = dv;
            GridView1.DataBind();
        }
    }

    private DataView BindGrid()
    {
        ds = new Query(AnthemWeb.DAL.Item.Schema).ExecuteDataSet();

        if (ViewState["sortExpr"] != null)
        {
            dv = new DataView(ds.Tables[0]);
            dv.Sort = (string)ViewState["sortExpr"];
        }
        else
        {
            dv = ds.Tables[0].DefaultView;
        }

        return dv;
    }

    protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
    {
        GridView1.PageIndex = e.NewPageIndex;
        GridView1.DataSource = BindGrid();
        GridView1.DataBind();
    }

    protected void GridView1_Sorting(object sender, GridViewSortEventArgs e)
    {
        string stExp = e.SortExpression;
        string stDir = string.Empty;
        if (SortDir == SortDirection.Ascending)
        {
            SortDir = SortDirection.Descending;
            stDir = "DESC";
        }
        else
        {
            SortDir = SortDirection.Ascending;
            stDir = "ASC";
        }

        ViewState["sortExpr"] = e.SortExpression + " " + stDir;
        GridView1.DataSource = BindGrid();
        GridView1.DataBind();
    }

    protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
    {
        int selectedRowIndex;
        selectedRowIndex = GridView1.SelectedIndex;
        GridViewRow row = GridView1.Rows[selectedRowIndex];
        string ID = row.Cells[0].Text;

        Response.Redirect("customer-details.aspx?ID=" + ID, false);
    }

    protected void btnSearch_Click(object sender, EventArgs e)
    {
        BindGrid();
    }