Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click

     
        Dim strwhere As String = ""
        Dim sql As String

        If CBL_1.SelectedValueList.ToString <> "" Then
            strwhere = " AND  (campo1 IN (" & CBL_1.SelectedValueList.ToString & "))"
        End If

        If CBL_2.SelectedValueList.ToString <> "" Then
            strwhere = strwhere & " AND  (campo2 IN (" & CBL_2.SelectedValueList.ToString & "))"
        End If

        ...

        sql = " SELECT campo1,campo2... " & _
                          " FROM tabella " & _
        " WHERE (1 = 1) " & strwhere

        lbl_sql.Text = sql

        Dim crystalReport As New ReportDocument()
        crystalReport.Load(Server.MapPath("~\Folder\nomereport.rpt"))
        Dim ds As DS_Catalogo = GetData(sql)
        crystalReport.SetDataSource(ds)
        CrystalReportViewer1.ReportSource = crystalReport
        CrystalReportViewer1.ID = "Catalogo_Disponibilita"

        If ds.Tables(0).Rows.Count = 0 Then
            lblmessage.Text = "Non ci sono dati con questi filtri !"
        Else
            lblmessage.Text = ""
        End If

    End Sub
    Private Function GetData(query As String) As DS_Catalogo
        Dim conString As String = ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString
        Dim cmd As New SqlCommand(query)
        Using con As New SqlConnection(conString)
            Using sda As New SqlDataAdapter()
                cmd.Connection = con
                sda.SelectCommand = cmd
                Using ds As New DS_Catalogo()
                    sda.Fill(ds, "DataTable1")
                    Return ds
                End Using
            End Using
        End Using
    End Function