Add total in VB.Net Gridview

Question

I can not manage to get the gridview display the total in a footer

I've tried the following:

<asp:GridView ID="GV" runat="server" 
    DataSourceID="SqlQuery" EmptyDataText="No data">
    <Columns>
        <asp:BoundField DataField="Weekday" FooterText=" " HeaderText="Weekday" />
        <asp:BoundField DataField="Volume" DataFormatString="{0:N0}" 
            FooterText="." HeaderText="Volume" />            
    </Columns>
 </asp:GridView>


Protected Sub GV_rowdatabound(sender As Object, e As GridViewRowEventArgs) Handles GV.RowDataBound
    Dim Volume as integer = 0
    For Each r As GridViewRow In GV.Rows
        If r.RowType = DataControlRowType.DataRow Then
            Volume = Volume + CDec(r.Cells(1).Text)
        End If
    Next
    GV.FooterRow.Cells(1).Text = Math.Round(Volume , 0)
End Sub

This gives me an error messages:

Object reference not set to an instance of an object

I followed advice in the following page and I changed the code: trying to total gridview in asp

Sub GV_WeekSumary_rowcreated(ByVal sender As Object, ByVal e As GridViewRowEventArgs)
    Dim Volume as integer = 0
    For Each r As GridViewRow In GV.Rows
        If r.RowType = DataControlRowType.DataRow Then
            Volume = Volume + CDec(r.Cells(1).Text)
        End If
    Next

    If e.Row.RowType = DataControlRowType.Footer Then
        e.Row.Cells(1).Text = Math.Round(Volume , 0)
    End If
End Sub

This does not give an error, but the footer does not show any value.

I've tried also the following:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    Dim Volume as integer = 0
    For Each r As GridViewRow In GV.Rows
        If r.RowType = DataControlRowType.DataRow Then
            Volume = Volume + CDec(r.Cells(1).Text)
        End If
    Next
    GV.FooterRow.Cells(1).Text = Math.Round(Volume, 0)
    GV.DataBind()
End Sub

Still no value in the footer, but when I debbug it I can see that footer is assisgned the value I need. Why it is not displayed in the website?

Any idea how I can get this to work?

Solution

You must use DataBound event.

Try this:

Protected Sub GV_DataBound(ByVal sender As Object, ByVal e As System.EventArgs) Handles GV.DataBound
    Dim Volume As Decimal = 0
    For Each r As GridViewRow In GV.Rows
        If r.RowType = DataControlRowType.DataRow Then
            Volume += Convert.ToDecimal(r.Cells(1).Text)
        End If
    Next
    GV.FooterRow.Cells(1).Text = Math.Round(Volume, 0).ToString()
End Sub