protected override void OnPreRender(EventArgs e)
{
base.OnInit(e);
GridView extendee =
this.NamingContainer.FindControl(this.ExtendeeID) as GridView;
if (extendee != null &&
extendee.AllowSorting &&
extendee.HeaderRow != null &&
!String.IsNullOrEmpty(extendee.SortExpression))
{
int field = GetSortField(extendee);
if (field >= 0)
{
Image img = new Image();
img.ImageUrl =
extendee.SortDirection == SortDirection.Ascending ?
this.AscendingImageUrl : this.DescendingImageUrl;
img.ImageAlign = ImageAlign.TextTop;
extendee.HeaderRow.Cells[field].Controls.Add(img);
}
}
}