Bi-Directional Sorting in Gridview

Given the following Grid (and c# code), how do I set it up to sort Ascending AND Descending on Header-Click? (The idea is to click the header once to sort in one direction, and upon the grid reload, to set the sort direction to go the other way on the next click).

ASPX page:
<asp:GridView ID="grdvwActivityStmt" CssClass="idGrid" CellPadding="3"
    AutoGenerateColumns="false" runat="server" Width="100%"
    EmptyDataText="No Activity Statements on file."
    AllowPaging="true" AllowSorting="true"
    PageSize="100" OnPageIndexChanging="grdvwActivityStmt_PageIndexChanging"
    OnSorting ="grdvwActivityStmt_OnSorting" DataKeyNames="SSN" GridLines="None">
    <HeaderStyle CssClass="ItemHeader" />
    <RowStyle CssClass="Item" />
    <AlternatingRowStyle CssClass="AltItem" />
    <PagerSettings FirstPageText="&lt;&lt; First&#160;&#160;&#160;" LastPageText="&#160;&#160;&#160;Last &gt;&gt;" PreviousPageText="&#160;&lt; Prev&#160;" NextPageText="&#160;Next &gt;&#160;" Mode="NextPreviousFirstLast" Position="TopAndBottom" />
    <PagerStyle Font-Bold="True" BackColor="#FFFFFF" CssClass="BlackBold" HorizontalAlign="Center" BorderStyle="None" />
    <Columns>
        <asp:templatefield headertext="ST" SortExpression="DestinationState">
            <ItemStyle HorizontalAlign="Center" Width="10%" />
            <HeaderStyle HorizontalAlign="Center" />
            <itemtemplate>
                <%# DataBinder.Eval(Container.DataItem, "DestinationState") %>
            </itemtemplate>
        </asp:templatefield>
        <asp:templatefield headertext="Acknowledgement" SortExpression="HistoryCreateDate">
            <HeaderStyle HorizontalAlign="Left" />
            <ItemStyle Width="30%" />
            <itemtemplate>
                <%# DataBinder.Eval(Container.DataItem, "HistoryCreateDate") %>
            </itemtemplate>
        </asp:templatefield>
        <asp:templatefield headertext="EFIN" SortExpression="EFIN">
            <HeaderStyle HorizontalAlign="Center" />
            <ItemStyle HorizontalAlign="Center" Width="15%" />
            <itemtemplate>
                <%# DataBinder.Eval(Container.DataItem, "EFIN") %>
            </itemtemplate>
        </asp:templatefield>
    </Columns>
</asp:GridView>

ASPX.CS page:

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

#region Page Load
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
            {
                dv = bindgrid(intAxaptaCustNum, strCustGUID);

                grdvwPgOne.DataSource = dv;
                grdvwPgOne.DataBind();
            }
    }
#endregion

#region Database Output Functions
    /// <summary>
    ///  Binding for the main gridView
    /// </summary>
    /// <returns></returns>
    private DataView bindgrid(string strAcctNum, string strCustGUID)
    {
        SqlConnection SQLConn = new SqlConnection(FCTaxContent.FCTaxContentConnectionString());
        SqlCommand sqlCmd = new SqlCommand("spx_GetInvoiceDataPageOne", SQLConn);
        sqlCmd.CommandType = CommandType.StoredProcedure;
        SqlDataAdapter sqlAdp = new SqlDataAdapter(sqlCmd);

        sqlCmd.Parameters.Add("@AcctNum", SqlDbType.VarChar);
        sqlCmd.Parameters["@AcctNum"].Value = strAcctNum;
        sqlCmd.Parameters.Add("@CustGUID", SqlDbType.VarChar);
        sqlCmd.Parameters["@CustGUID"].Value = strCustGUID;

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

        pnlActivityOutput.Visible = true;

        return dv;
    }

    /// <summary>
    ///  Sorting for the Header clicks in the main gridView
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    protected void grdvwPgOne_OnSorting(Object sender, GridViewSortEventArgs e)
    {
        if (e.SortDirection == SortDirection.Ascending)
        {
            ViewState["sortExpr"] = e.SortExpression;
        }
        else
        {
            ViewState["sortExpr"] = string.Concat(e.SortExpression, " ", SortDirection.Descending);
        }

        grdvwPgOne.DataSource = bindgrid(Session["AxaptaCustomerNumber"].ToString(), Session["AxaptaCustGUID"].ToString());
        grdvwPgOne.DataBind();

        pnlActivityOutput.Visible = true;
    }

    /// <summary>
    ///  Paging handler for the main gridView
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    protected void grdvwPgOne_PageIndexChanging(Object sender, GridViewPageEventArgs e)
    {
        grdvwPgOne.PageIndex = e.NewPageIndex;
        grdvwPgOne.DataSource = bindgrid(Session["AxaptaCustomerNumber"].ToString(), Session["AxaptaCustGUID"].ToString());
        grdvwPgOne.DataBind();

        pnlActivityOutput.Visible = true;
    }
#endregion


I'd give more points if there was a way, as this one has stumped me for quite some time.
LVL 3
Paul KahlAsked:
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topdog770Connect With a Mentor Commented:
The grdvwPgOne_OnSorting function doesn't appear to try and change anything in terms of direction though or look at which direction was used to sort the last time into the function.. it just looks at the direction passed into the function and sorts in the specified direction.

It looks like you would need to call the grdvwPgOne_OnSorting from another function and manipulate the e.SortDirection argument to make any change.

thinking very simply... and not as complete snippet, I was thinking something like this

 protected void grdvwPgOne_OnSorting(Object sender, GridViewSortEventArgs e)
    {
        if( Session["LastSortDirection"].ToString() == "asc" )
        {
            ViewState["sortExpr"] = string.Concat(e.SortExpression, " ", SortDirection.Descending);
            Session["LastSortDirection"] = "desc";
        }
       else
      {  // default to ascending order if session variable not set...
            Session["LastSortDirection"] = "asc";
            ViewState["sortExpr"] = e.SortExpression;
     }

        grdvwPgOne.DataSource = bindgrid(Session["AxaptaCustomerNumber"].ToString(), Session["AxaptaCustGUID"].ToString());
        grdvwPgOne.DataBind();

        pnlActivityOutput.Visible = true;
    }
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topdog770Commented:
I'm sure I'm missing something, but..

Why not store which direction the grid was sorted by last time and do the opposite direction next time the user asks for a sort?
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Paul KahlAuthor Commented:
Store it how? Session based? The idea is NOT to pass it through the query string. I want to prevent users (or abusers, really) from hacking urls and doing what they want, so I'd like to keep it in code.
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topdog770Commented:
Yeah.. i admit I was thinking session based....

Another option would be to create your own derived DataGrid class and allow sorting logic to be handled with the object itself..

benefits would include not having to rely on outside source of control or information to determine control behavior.. ie session variable and or parameter and redundantly, cleaner implementation with the exact functionality you are wanting.
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Paul KahlAuthor Commented:
That's already what I'm doing, actually. I have a built-in sort functionality in the grdvwPgOne_OnSorting function, but I can't get it to switch directions.
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Paul KahlAuthor Commented:
By jove, I think you've got it!

Here's the finished version, with detection for the object of session content.

protected void grdvwPgOne_OnSorting(Object sender, GridViewSortEventArgs e)
    {
        object objSortDir = Session["LastSortDirection"];
        if (!(objSortDir is object))
        {
            Session["LastSortDirection"] = "asc";
            ViewState["sortExpr"] = e.SortExpression;
        }
        else
        {
            if (Session["LastSortDirection"].ToString() == "asc")
            {
                ViewState["sortExpr"] = string.Concat(e.SortExpression, " desc");
                Session["LastSortDirection"] = "desc";
            }
            else
            {
                Session["LastSortDirection"] = "asc";
                ViewState["sortExpr"] = e.SortExpression;
            }
        }

        grdvwPgOne.DataSource = bindgrid(Session["AxaptaCustomerNumber"].ToString(), Session["AxaptaCustGUID"].ToString());
        grdvwPgOne.DataBind();

        pnlPg1.Visible = true;
    }
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topdog770Commented:
Cool!
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