asp.net - GridView sorting: SortDirection always Ascending

Question

I have a gridview and I need to sort its elements when the user clicks on the header.
Its datasource is a List object.

The aspx is defined this way :

<asp:GridView ID="grdHeader" AllowSorting="true" AllowPaging="false" 
    AutoGenerateColumns="false" Width="780" runat="server"  OnSorting="grdHeader_OnSorting" EnableViewState="true">
    <Columns>
        <asp:BoundField DataField="Entitycode" HeaderText="Entity" SortExpression="Entitycode" />
        <asp:BoundField DataField="Statusname" HeaderText="Status" SortExpression="Statusname" />
        <asp:BoundField DataField="Username" HeaderText="User" SortExpression="Username" />
    </Columns>
</asp:GridView>

The code behind is defined this way :
First load :

protected void btnSearch_Click(object sender, EventArgs e)
{
    List<V_ReportPeriodStatusEntity> items = GetPeriodStatusesForScreenSelection();
    this.grdHeader.DataSource = items;
    this.grdHeader.DataBind();
}

when the user clicks on headers :

protected void grdHeader_OnSorting(object sender, GridViewSortEventArgs e)
{
    List<V_ReportPeriodStatusEntity> items = GetPeriodStatusesForScreenSelection();
    items.Sort(new Helpers.GenericComparer<V_ReportPeriodStatusEntity>(e.SortExpression, e.SortDirection));
    grdHeader.DataSource = items;
    grdHeader.DataBind();
}

My problem is that e.SortDirection is always set to Ascending.
I have webpage with a similar code and it works well, e.SortDirection alternates between Ascending and Descending.

What did I do wrong ?

Answer 1

The problem with Session and Viewstate is that you also have to keep track of the gridview control for which SortColumn and Direction is stored if there is more than one gridview on the page.

An alternative to Session and Viewstate is to add 2 attributes to the Gridview and keep track of Column and Direction that way.

Here is an example:

private void GridViewSortDirection(GridView g, GridViewSortEventArgs e, out SortDirection d, out string f)
{
    f = e.SortExpression;
    d = e.SortDirection;

    //Check if GridView control has required Attributes
    if (g.Attributes["CurrentSortField"] != null && g.Attributes["CurrentSortDir"] != null)
    {
        if (f == g.Attributes["CurrentSortField"])
        {
            d = SortDirection.Descending;
            if (g.Attributes["CurrentSortDir"] == "ASC")
            {
                d = SortDirection.Ascending;
            }
        }

        g.Attributes["CurrentSortField"] = f;
        g.Attributes["CurrentSortDir"] = (d == SortDirection.Ascending ? "DESC" : "ASC");
    }

}