Gridview sorting up/down arrow in column headers - asp.net

Question

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>

Answer 1

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.

Answer 2

In Order to add a sorting arrow in a Data Grid on a VB.net Windows Form, you don't even have to write any code
On form in Design Mode - select the grid you are working with, right click go to properties, set Selection Mode = Cell Select
On form in Design Mode - click the arrow on the grid on the right up, to edit column properties, select edit or add columns, set SortMode = Automatic
If you have code for your cell content (say you want user to open another form while clicking on any row in the data grid) then use CellDoubleClick property to handle the event. If the you have used single click then it will sort the header and also open the form for the given cell
Private Sub _CellDoubleClick(sender As Object, e As DataGridViewCellEventArgs) Handles DGAcctGrpList.CellDoubleClick