记录只能前移一条或后称一条

阿泰，我用rs.movenext和rs.moveprevious遇到的怪问题，用movenext就是当记录在第一条时，只能前移一条，用moveprevious记录只能后移一条。
相关代码：
Private Sub OpenRs()----打开RS
Dim sqlstr As String
If cn.State <> adStateClosed Then cn.Close
cn.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=E:\VBDtatabase\mfdatabase.mdb;Persist Security Info=False"
cn.CursorLocation = adUseClient
cn.Open
sqlstr = "select * from Detailtb"
If rs.State <> adStateClosed Then rs.Close
rs.Open sqlstr, cn, adOpenDynamic, adLockOptimistic
End Sub
选择下一条：
Private Sub CmdNext_Click()
Call OpenRs
If Not rs.EOF Then
If rs.BOF Then
rs.MoveLast
Else
rs.MoveNext
Call Viewdata
End If
Else
MsgBox "已經是最後一條記錄，請重新選擇!", vbOKOnly
End If
End Sub
选择上一条：
Private Sub CmdPrevious_Click()
Call OpenRs
If Not rs.BOF Then
rs.MovePrevious
If rs.BOF Then
rs.MoveLast
Call Viewdata
End If
End If
End Sub