VB 判斷是否文本文件

Option Explicit
'*************************************************************************
'**作 者：新興網絡
'**原 文：http://www.71216532.buzz/Tech/Program/VisualBasic/666.html
'**如果需要轉載，請保留作者信息謝謝
'*************************************************************************
Public Function IsTextFile(Bytes() As Byte) As Boolean
        Dim i As Long, AscN As Long, Length As Long
        Length = UBound(Bytes) + 1
       
        If Length < 3 Then
            IsTextFile = IsGB(Bytes, Length)
            Exit Function
        ElseIf Bytes(0) = &HEF And Bytes(1) = &HBB And Bytes(2) = &HBF Then
            IsTextFile = True
            Exit Function
        End If

        Do While i <= Length - 1
            If Bytes(i) < 128 Then
                i = i + 1
                AscN = AscN + 1
            ElseIf (Bytes(i) And &HE0) = &HC0 And (Bytes(i + 1) And &HC0) = &H80 Then
                i = i + 2

            ElseIf i + 2 < Length Then
                If (Bytes(i) And &HF0) = &HE0 And (Bytes(i + 1) And &HC0) = &H80 And (Bytes(i + 2) And &HC0) = &H80 Then
                     i = i + 3
                Else
                    IsTextFile = IsGB(Bytes, Length)
                    Exit Function
                End If
            Else
                IsTextFile = IsGB(Bytes, Length)
                Exit Function
            End If
        Loop
               
        If AscN = Length Then
            IsTextFile = IsGB(Bytes, Length)
        Else
            IsTextFile = True
        End If

End Function

Private Function IsGB(Bytes() As Byte, FileSize As Long) As Boolean
    Dim ObjStream As Object, ret As String
    Set ObjStream = CreateObject("ADODB.Stream")
    With ObjStream
        .Type = 1
        .Mode = 3
        .open
        .Write Bytes
        .Position = 0
        .Type = 2
        .Charset = "GB2312"
        ret = .ReadText
       .Close
    End With
    If LenB(StrConv(ret, vbFromUnicode)) = FileSize Then
        IsGB = True
    Else
        IsGB = False
    End If
End Function