recordset的close和nothing的区别？

登陆窗体，之前是

rs.close

Set rs = Nothing

这样点确定之后，提示对象已关闭，无法进行操作。后来把close去掉就好了。

不解的是，清空不是对象不存在了吗？先关闭再清空和直接清空最后有什么不一样？

Option Compare Database
Option Explicit

Private Sub OK_Click()
  Dim strSql As String
  Dim rs As ADODB.Recordset
  Set rs = New ADODB.Recordset
   If IsNull(Me.username) Or Me.username = "" Then
      DoCmd.Beep
      MsgBox ("请输入用户名称！")
   ElseIf IsNull(Me.Password) Or Me.Password = "" Then
      DoCmd.Beep
      MsgBox "请输入密码！"
   Else
      strSql = "select * from 管理员 where 用户名='" & Me.username & "' and 密码 = '" & Me.Password & "'"
      Set rs = GetRs(strSql)
      If rs.EOF Then
         DoCmd.Beep
         MsgBox ("用户名或密码错误！")
         Me.username = ""
         Me.Password = ""
         Me.username.SetFocus
         Exit Sub
      Else
         DoCmd.Close
         check = True
         DoCmd.OpenForm ("主切换面板")
      End If
   End If
   Set rs = Nothing

End Sub