How to check to see if file is open?

Function OpenFile(Filename$, Mode%, RLock%, RecordLen%) As Integer
    Const REPLACEFILE = 1, READAFILE = 2, ADDTOFILE = 3
    Const RANDOMFILE = 4, BINARYFILE = 5
    Const NOLOCK = 0, RDLOCK = 1, WRLOCK = 2, RWLOCK = 3
    Dim ErrorCode As Long
    Dim FileNum%, Action%, LockFlg%
    LockFlg% = 0
    FileNum% = FreeFile
    On Error GoTo OpenErrors
    Select Case Mode
        Case REPLACEFILE
            Select Case RLock%
                Case NOLOCK
                    Open Filename For Output Shared As FileNum%
                Case RDLOCK
                    Open Filename For Output Lock Read As FileNum%
                Case WRLOCK
                    Open Filename For Output Lock Write As FileNum%
                Case RWLOCK
                    Open Filename For Output Lock Read Write As FileNum%
            End Select
        Case READAFILE
            Select Case RLock%
                Case NOLOCK
                    Open Filename For Input Shared As FileNum%
                Case RDLOCK
                    Open Filename For Input Lock Read As FileNum%
                Case WRLOCK
                    Open Filename For Input Lock Write As FileNum%
                Case RWLOCK
                    Open Filename For Input Lock Read Write As FileNum%
            End Select
        Case ADDTOFILE
            Select Case RLock%
                Case NOLOCK
                    Open Filename For Append Shared As FileNum%
                Case RDLOCK
                    Open Filename For Append Lock Read As FileNum%
                Case WRLOCK
                    Open Filename For Append Lock Write As FileNum%
                Case RWLOCK
                    Open Filename For Append Lock Read Write As FileNum%
            End Select
        Case RANDOMFILE
            Select Case RLock%
                Case NOLOCK
                    Open Filename For Random Shared As FileNum% Len = RecordLen%
                Case RDLOCK
                    Open Filename For Random Lock Read As FileNum% Len = RecordLen%
                Case WRLOCK
                    Open Filename For Random Lock Write As FileNum% Len = RecordLen%
                Case RWLOCK
                    Open Filename For Random Lock Read Write As FileNum% Len = RecordLen%
            End Select
        Case BINARYFILE
            Select Case RLock%
                Case NOLOCK
                    Open Filename For Binary Shared As FileNum%
                Case RDLOCK
                    Open Filename For Binary Lock Read As FileNum%
                Case WRLOCK
                    Open Filename For Binary Lock Write As FileNum%
                Case RWLOCK
                    Open Filename For Binary Lock Read Write As FileNum%
            End Select
        Case Else
          Exit Function
    End Select
    OpenFile = FileNum%
    Exit Function
OpenErrors:
    If Err = 70 Then  'File is locked, try 3 times
        LockFlg% = LockFlg% + 1
        Debug.Print "File Locked!"
        If LockFlg > 3 Then GoTo OpenErrCont
        Resume
    End If
OpenErrCont:
    ErrorCode = Err
    Action% = FileErrors(ErrorCode)
    Select Case Action%
        Case 0
          Resume            'Resumes at line where ERROR occured
        Case 1
            Resume Next     'Resumes at line after ERROR
        Case 2
            OpenFile = 0     'Unrecoverable ERROR-reports error, exits function with error code
            Exit Function
        Case Else
            MsgBox Error$(Err) + vbCrLf + "After line " + Str$(Erl) + vbCrLf + "Program will TERMINATE!"
            'Unrecognized ERROR-reports error and terminates.
            End
    End Select
End Function

Function FileErrors(errVal As Long) As Integer
    Dim Msg$, msgType%, Response%
'Return Value 0=Resume,              1=Resume Next,
'             2=Unrecoverable Error, 3=Unrecognized Error
msgType% = 48
Select Case errVal
    Case 68
      Msg$ = "That device appears Unavailable."
      msgType% = msgType% + 4
    Case 71
      Msg$ = "Insert a Disk in the Drive"
    Case 53
      Msg$ = "Cannot Find File"
      msgType% = msgType% + 5
   Case 57
      Msg$ = "Internal Disk Error."
      msgType% = msgType% + 4
    Case 61
      Msg$ = "Disk is Full.  Continue?"
      msgType% = 35
    Case 64, 52
      Msg$ = "That Filename is Illegal!"
    Case 70
      Msg$ = "File in use by another user!"
      msgType% = msgType% + 5
    Case 76
      Msg$ = "Path does not Exist!"
      msgType% = msgType% + 2
    Case 54
      Msg$ = "Bad File Mode!"
    Case 55
      Msg$ = "File is Already Open."
    Case 62
      Msg$ = "Read Attempt Past End of File."
    Case Else
      FileErrors = 3
      Exit Function
  End Select
  FileErrors = 2
End Function