I am developing a site in ASP.Net and VB.Net that will enable users to sort data in a GridView in Ascending or Descending order.

The records are coming from an SQL Server Express database.

I go to click on a column heading to sort the data and I get the following error:

'Conversion from string "DESC" to type 'Double' is not valid.'

Below is the code I am using for the sorting:

Code:
Protected Sub Button3_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button3.Click

Dim sqlConn As New SqlConnection
Dim sqlCmd As New SqlClient.SqlCommand
Dim sqlReader As SqlDataReader

'If no values are supplied in the textbox, throw an error message.
If TextBox2.Text = "" Then
MsgBox("A centre code needs to be provided...")
End If

If TextBox2.Text <> "" Then

'Telling the system the location of the database.
sqlConn.ConnectionString = "server=servername;Initial Catalog=dbName;Trusted_Connection=yes"

'Here we are opening the connection to the database.
sqlConn.Open()

'This is to say that sqlCmd is a stored procedure.
sqlCmd.CommandType = System.Data.CommandType.StoredProcedure

'This is creating the command to execute the stored procedure based on the information given in the connection string.
sqlCmd = sqlConn.CreateCommand

'The command is triggered to execute the stored procedure which grabs all information for the specific centre.
sqlCmd.CommandText = "exec ProcedureName'" & TextBox2.Text & "' "

'This will read the rows in the database.
sqlReader = sqlCmd.ExecuteReader()

GridView2.Columns.Clear() 'If there are rows of data that match are criteria
If (sqlReader.HasRows) Then

'The rows of data are grabbed for the specific centre from the database using the data reader.
GridView2.DataSource = sqlReader
GridView2.DataBind()
GridView2.Columns.Clear()
Else
MsgBox("The centre code provided does not exist...")
End If

'This is closing the connection to the database once we have finished with it.
sqlConn.Close()

'This is to clear the list of items out of the GridView box.

End If

End Sub

Property GridViewSortDirection() As String
Get
If IsNothing(ViewState.Item("GridViewSortDirection")) Then
Return "desc"
End If
Return ViewState.Item("GridViewSortDirection")
End Get

Set(ByVal Value As String)
ViewState.Item("GridViewSortDirection") = Value
End Set

End Property

Function GetSortDirection() As String

Dim GridViewSortDirectionNew As String

Select Case GridViewSortDirection

Case "DESC"
GridViewSortDirectionNew = "ASC"

Case "ASC"
GridViewSortDirectionNew = "DESC"

Case Else
GridViewSortDirectionNew = "DESC"

End Select
GridViewSortDirection = GridViewSortDirectionNew

Return GridViewSortDirectionNew

End Function

Protected Sub GridView_Sorting1(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewSortEventArgs) Handles GridView2.Sorting

Dim myPageIndex As Integer = GridView2.PageIndex
Dim mySortdirection As String = GetSortDirection()
Dim sortExpression = e.SortExpression
Dim dv As New DataView()


If (GridViewSortDirection = SortDirection.Ascending) Then

GridViewSortDirection = SortDirection.Descending
'SortGridView(sortExpression, "DESCENDING")
Else
GridViewSortDirection = SortDirection.Ascending

End If


'dv.Table = GridView2.DataSource

' dv.Sort = e.SortExpression & " " & mySortdirection
' GridView2.DataSource = dv
'
' GridView2.DataBind()
'
' GridView2.PageIndex = myPageIndex

End Sub

'Protected Sub SortGridView(string sortExpression,string direction)

'DataTable dt = GetData().Tables[0]

' DataView(GridView2 = New DataView(GridView2))
' GridView2.Sort = sortExpression + Direction
'
' GridView1.DataSource = GridView2
' GridView1.DataBind()
'
' End Sub
My GridView looks like:

Code:
 

< asp:GridView ID="GridView2" runat="server" Height="143px" AllowSorting="true" OnSorting="GridView_Sorting1"
How can I get past this problem?

All help and advice will be greatly appreciated.

Many thanks,

Dan