VB.Net Data GridView

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VB

.NET

Private Sub btnShow_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnShow.Click
        Try
            con.query = "SELECT challan.cno, merchant.mname, challan.cdate, challan.total FROM merchant INNER JOIN challan ON merchant.mno = challan.mno WHERE ((challan.cdate Between #" + from.ToString + "# And #" + upto.ToString + "#) AND (challan.mno=" + mno.ToString + "))"

            con.openConnection()
            con.objadp = New OleDbDataAdapter(con.query, con.objcon)
            bulider = New OleDbCommandBuilder(con.objadp)
            dt.Rows.Clear()
            con.objadp.Fill(dt)
            dgvChallanList.DataSource = dt
            dgvChallanList.Columns(0).HeaderText = "Challan No"
            dgvChallanList.Columns(1).HeaderText = "Date"
            dgvChallanList.Columns(2).HeaderText = "Merchant Name"
            dgvChallanList.Columns(3).HeaderText = "Total"
            Dim r As Integer = dt.Rows.Count
            Dim tot As Long = 0
            For i As Integer = 0 To r - 1 Step 1
                tot += dgvChallanList.Rows(i).Cells("Total").Value
            Next
            lblTotal.Text = tot.ToString("00")
        Catch ex As Exception
            MessageBox.Show(ex.Message.ToString)
        Finally
            con.closeConnection()
        End Try
    End Sub

In this Con is a Connection object which can do all the task related to connection and it is a base class also..so that con object can use all the member from that class.
The main Problem is that here Datagridview will not be filled..Can u Help me ???