Sorting a GridView

http://geekswithblogs.net/azamsharp/archive/2006/04/27/76612.aspx

This code from Azam Sharp works well ^_^


private const string ASCENDING = " ASC";
 private const string DESCENDING = " DESC";
 public SortDirection GridViewSortDirection
    {
        get
        {
            if (ViewState["sortDirection"] == null)
                ViewState["sortDirection"] = SortDirection.Ascending;

            return (SortDirection) ViewState["sortDirection"];               
        }
        set { ViewState["sortDirection"] = value; }
    }


    protected void GridView1_Sorting(object sender, GridViewSortEventArgs e)
    {
        string sortExpression = e.SortExpression;

        if (GridViewSortDirection == SortDirection.Ascending)
        {
            GridViewSortDirection = SortDirection.Descending;
            SortGridView(sortExpression, DESCENDING);
        }
        else
        {
            GridViewSortDirection = SortDirection.Ascending;
            SortGridView(sortExpression, ASCENDING);
        }  
      
    }

    private void SortGridView(string sortExpression,string direction)
    {
        //  You can cache the DataTable for improving performance
        DataTable dt = GetData().Tables[0];

        DataView dv = new DataView(dt);
        dv.Sort = sortExpression + direction;        

        GridView1.DataSource = dv;
        GridView1.DataBind();        
    }