How to implement Select on a GridView1 with Paging enabled.

How to implement Select on a GridView1 with Paging enabled based on a DataTable.

    protected void GridView1_SelectedIndexChanging(object sender, GridViewSelectEventArgs e)
    {
        // e.NewSelectedIndex -> 0 to n
        // GridView1.PageCount -> (n-1) always 
        // GridView1.PageIndex -> 0 to Page#
        int rowN = 1 + ((GridView1.PageCount-1) * GridView1.PageIndex + e.NewSelectedIndex);
        DetailsView1.HeaderText = "Details View of Row "+ rowN.ToString();
        DetailsView1.PageIndex = rowN - 1;
        GridView1.SelectedIndex = rowN - 1;
        DetailsView1.DataSource = Cache["dt"];        
        DetailsView1.DataBind();
    }