Gridview sorting up/down arrow in column headers

asp.net, gridview, paging, sorting, vb.net

Solution

Take a look at my sample:

<asp:GridView ID="GridView1" runat="server" AllowPaging="True" 
    AllowSorting="True" AutoGenerateColumns="False" DataKeyNames="CustomerId" 
    DataSourceID="SqlDataSource1">
    <SortedAscendingHeaderStyle CssClass="sortasc" />
    <SortedDescendingHeaderStyle CssClass="sortdesc" />
    <Columns>
        <asp:CommandField ShowSelectButton="True" />
        <asp:BoundField DataField="CustomerId" HeaderText="CustomerId" 
            InsertVisible="False" ReadOnly="True" SortExpression="CustomerId" />
        <asp:BoundField DataField="Name" HeaderText="Name" SortExpression="Name" />
        <asp:BoundField DataField="IdNumber" HeaderText="IdNumber" 
            SortExpression="IdNumber" />
    </Columns>
</asp:GridView>

Pay attention on SortedAscendingHeaderStyle and SortedDescendingHeaderStyle. Just create apropriate css classes with background image (arrow up and arrow down) and you are done.

Problem

I'm currently working on some code which is taking care of sorting and paging data in a gridview. I'm now trying to implement sorting arrow (up/down arrows next to column headers) but I have no success. The code to implement the sorting arrows is located in the *GridView1_RowCreated* sub routine. Right now, when I run the code, I don't see the sorting arrows at all. The problematic line is the following one: "If tblAdministrators.SortExpression = lnk.CommandArgument Then" I can't figure out what's wrong with that line. It's always False therefore the arrows don't show up. ``` Private Function GetData(sort As SortDirection) As Data.DataView Dim connection As OracleDBConnect = DAL.GetOracleDBConnection() Dim request As OracleDBRequest = Nothing Dim result As OracleDBResult = Nothing Dim trace As OracleDBChronoTrace = Nothing Dim status As DBStatus Dim sb As New StringBuilder Dim dv As DataView With sb .Append("SELECT * FROM USERS") End With request = New OracleDBRequest(sb.ToString, CommandType.Text) status = connection.Execute(request, result, trace) dv = New DataView(result.DataSet.Tables(0)) If (ViewState("sortExp") IsNot Nothing) Then dv = New Data.DataView(result.DataSet.Tables(0)) If (GridViewSortDirection = SortDirection.Ascending) Then GridViewSortDirection = SortDirection.Descending dv.Sort = CType(ViewState("sortExp").ToString() & DESCENDING, String) Else GridViewSortDirection = SortDirection.Ascending dv.Sort = CType(ViewState("sortExp").ToString() & ASCENDING, String) End If Else dv = result.DataSet.Tables(0).DefaultView End If Return dv End Function Public Property GridViewSortDirection() As SortDirection Get If ViewState("sortDir") Is Nothing Then ViewState("sortDir") = SortDirection.Ascending End If Return CType(ViewState("sortDir"), SortDirection) End Get Set(ByVal value As SortDirection) ViewState("sortDir") = value End Set End Property Protected Sub GridView1_PageIndexChanging(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewPageEventArgs) Handles tblAdministrators.PageIndexChanging tblAdministrators.PageIndex = e.NewPageIndex GridViewSortDirection = If(GridViewSortDirection = SortDirection.Descending, SortDirection.Ascending, SortDirection.Descending) tblAdministrators.DataSource = GetData(GridViewSortDirection) tblAdministrators.DataBind() End Sub Protected Sub GridView1_Sorting(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewSortEventArgs) Handles tblAdministrators.Sorting ViewState("sortExp") = e.SortExpression tblAdministrators.DataSource = GetData(GridViewSortDirection) tblAdministrators.DataBind() End Sub Protected Sub GridView1_RowCreated(sender As Object, e As GridViewRowEventArgs) Handles tblAdministrators.RowCreated If e.Row.RowType = DataControlRowType.Header Then For Each tc As TableCell In e.Row.Cells If tc.HasControls() Then Dim lnk As LinkButton = DirectCast(tc.Controls(0), LinkButton) If lnk IsNot Nothing Then Dim img As New System.Web.UI.WebControls.Image() img.ImageUrl = "/images/" & (If(GridViewSortDirection = SortDirection.Ascending, "asc", "desc")) & ".gif" If tblAdministrators.SortExpression = lnk.CommandArgument Then tc.Controls.Add(New LiteralControl(" ")) tc.Controls.Add(img) End If End If End If Next End If End Sub ``` ASPX code: ``` <asp:GridView ID="tblAdministrators" runat="server" AutoGenerateColumns="false" EmptyDataText="No records found" PageSize="25" AllowPaging="True" AllowSorting="True" OnRowCreated="GridView1_RowCreated"> <Columns> <asp:BoundField HeaderText="Name" DataField="Name" SortExpression="NAME"></asp:BoundField> </Columns> <Columns> <asp:BoundField HeaderText="City" DataField="City" SortExpression="CITY"></asp:BoundField> </Columns> </asp:GridView> ```

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