I have ported this method to vb.net, please see source code (II)

#Region "from Pinyin to Pinyin"
Public Shared Function getpytopy (ByVal pystr as String, _
Optional ByVal Iscomp as Boolean = False) as String
If pystr.length = 0 Then Exit Function

miscompelled = Iscomp

Dim Tonesite as Integer
Dim Tonevalue as Integer
Dim Tonechar as Char

Tonesite = Gettonesite (PYSTR)
If tonesite =-1 Then
Return PYSTR
ElseIf Tonesite <-1 Then
Exit Function
End If

Tonevalue = Gettonevalue (Pystr, Tonesite)
If Tonevalue =-1 Then Exit Function

If miscompelled Then
Tonechar = Gettonechar (Pystr, toneSite-1)
Else
Tonechar = Gettonechar (PYSTR)
End If
If not Ispychar (Tonechar) Then Exit Function
return conversion (PYSTR, Tonesite, Tonevalue, Tonechar)

End Function
' Returns a position indicating the number of tones
Private Shared Function gettonesite (ByVal pystr as String) as Integer
If pystr.length = 0 Then Exit Function
Dim I As Integer, j As Integer = 0
' Check that there are several numbers in the string
For i = 0 to Pystr.length-1
If Char.isnumber (Pystr.chars (i)) Then
J + 1
End If
Next
If j = 0 Then ' No digits, that is, no value indicating the tone
Return-1
ElseIf j = 1 Then ' has a number, legal
For i = 0 to Pystr.length-1
If Char.isnumber (Pystr.chars (i)) Then
return I
End If
Next
Else ' There are multiple numbers, illegal, return the opposite number
Return-j
End If
End Function
' Return tone is a few voices
Private Shared Function gettonevalue (ByVal pystr as String, _
ByVal Site As Integer) As Integer
If pystr.length = 0 Then Exit Function
If Site >= 0 Then
Dim value as Char = Pystr.chars (Site)
Dim Num as Integer
If Char.isnumber (value) Then
num = CType (value. ToString, Integer)
If num >= 0 and num <= 4 Then
Return num
Else
Return-1
End If
Else
Return-1
End If
End If
End Function
' Return the letter to mark the tone
Private Shared Function Gettonechar (ByVal pystr as String, _
ByVal Site as Integer) as Char
If pystr.length = 0 Then Exit Function
If Site >= 0 Then
Dim value as Char = Pystr.chars (Site)
return value
End If
End Function
Private Shared Function Gettonechar (ByVal pystr as String) as Char
If pystr.length = 0 Then Exit Function
Dim Chr as Char

If Pystr.indexof (A (0)) >= 0 Then
CHR = Pystr.chars (Pystr.indexof (A (0)))
ElseIf pystr.indexof (o (0)) >= 0 Then
CHR = Pystr.chars (Pystr.indexof (o (0)))
ElseIf Pystr.indexof (E (0)) >= 0 Then
CHR = Pystr.chars (Pystr.indexof (E (0)))
ElseIf Pystr.indexof (i (0)) >= 0 Then
CHR = Pystr.chars (Pystr.indexof (i (0)))
ElseIf pystr.indexof (U (0)) >= 0 Then
CHR = Pystr.chars (pystr.indexof (U (0)))
ElseIf Pystr.indexof (V (0)) >= 0 Then
CHR = Pystr.chars (Pystr.indexof (V (0)))
End If

Return CHR
End Function
' Judge whether the phonetic characters are valid
Private Shared Function Ispychar (ByVal chr as Char) as Boolean
Select Case CHR
Case "a" C
Return True
Case "O" C
Return True
Case "E" C
Return True
Case "I" C
Return True
Case "U" c
Return True
Case "V" c
Return True
Case Else
Return False
End Select
End Function
' Convert
Private Shared Function conversion (ByVal Pystr as String, _
ByVal Tonesite as Integer, _
ByVal Tonevalue as Integer, _
ByVal Tonechar as Char) as String
If tonevalue >= 1 and tonevalue <= 4 Then
Select Case Tonechar
Case "a"
Pystr = Pystr.replace (Tonechar, A (tonevalue). Chars (0))
Case "O"
Pystr = Pystr.replace (Tonechar, O (tonevalue). Chars (0))
Case "E"
Pystr = Pystr.replace (Tonechar, E (tonevalue). Chars (0))
Case "I"
Pystr = Pystr.replace (Tonechar, I (Tonevalue). Chars (0))
Case "U"
Pystr = Pystr.replace (Tonechar, U (tonevalue). Chars (0))
Case "V"
Pystr = Pystr.replace (Tonechar, V (tonevalue). Chars (0))
End Select
Pystr = Pystr.replace (tonevalue.tostring, "")
Return PYSTR
End If
End Function
#End Region

#Region "from Chinese to Pinyin"
Public Shared Function gethztopy (ByVal hzstr as String, _
Optional ByVal tonevalue as Integer = 0, _
Optional ByVal Iscomp as Boolean = False) as String
' ByVal Tonevalue as Integer, _
If hzstr.length = 0 Then Exit Function
If pylist.count = 0 Then loadpychars ()
miscompelled = Iscomp
If miscompelled Then
Else
Dim tmpstr as String = ""
Dim I as Integer
Dim Num as Integer
For i = 1 to Hzstr.length
num = ASC (HZSTR)
Debug.WriteLine (Num. ToString)
TMPSTR = Getpychars (num)
Tmpstr = Getpytopy (Tmpstr & Tonevalue)
Return TMPSTR
Next
End If
End Function

Private Shared Function getpychars (ByVal num as Integer) as String
If num > 0 and num < 160 Then
return Chr (num)
Else
If num < -20319 Or num > -10247 Then
Return ""
Else
Dim I, value as Integer
For i = pylist.count-1 to 0 Step-1
If Pylist.getbyindex (i) <= num Then Exit for
Next
' Value = CType (Pylist.getbyindex (i), Integer)
return Pylist.getkey (i). Tostring
End If
End If
End Function
#End Region

End Class