如何使用VB.NET生成随机串或数字？

Public Enum stringtype
  allstring = 1  '大小写字母
  allnumic = 2  '数字
  str_num = 3  '大小写字母+数字
  str_upper = 4  '大写字母
  str_lower = 5 '大写字母 
 End Enum
 Function GenerateRandom(ByVal Length As Integer, ByVal s As stringtype) As String
  Dim strtemp As String = ""
  Dim constant() As String = Nothing
  Select Case s
   Case stringtype.allnumic
    strtemp = "0,1,2,3,4,5,6,7,8,9"
    constant = strtemp.Split(",")
   Case stringtype.allstring
    strtemp = "a,b,c,d,e,f,g,h,i,j,k,m,n,o,p,q,r,s,t,u,v,w,x,y,z,A,B,C,D,E,F,D,G,H,I,J,K,L,M,N,P,Q,R,S,T,U,V,W,X,X,Y,Z"
    constant = strtemp.Split(",")
   Case stringtype.str_lower
    strtemp = "a,b,c,d,e,f,g,h,i,j,k,m,n,o,p,q,r,s,t,u,v,w,x,y,z"
    constant = strtemp.Split(",")
   Case stringtype.str_num
    strtemp = "a,b,c,d,e,f,g,h,i,j,k,m,n,o,p,q,r,s,t,u,v,w,x,y,z,A,B,C,D,E,F,D,G,H,I,J,K,L,M,N,P,Q,R,S,T,U,V,W,X,X,Y,Z,0,1,2,3,4,5,6,7,8,9"
    constant = strtemp.Split(",")
   Case stringtype.str_upper
    strtemp = "A,B,C,E,F,D,G,H,I,J,K,L,M,N,P,Q,R,S,T,U,V,W,X,Y,Z"
    constant = strtemp.Split(",")
  End Select
  Dim NewRandom As System.Text.StringBuilder = New System.Text.StringBuilder(Length)
  Dim rd As Random = New Random()
  Dim i As Integer
  For i = 0 To Length - 1 Step i + 1
   NewRandom.Append(constant(rd.Next(constant.Length - 1)))
  Next
  Return NewRandom.ToString()
 End Function

Public Function GetOAuthNonce() As String ' 得到随机值
  Dim result As String = System.Guid.NewGuid().ToString()
  result = result.Replace("-", "")
  Return result.Substring(0, 10)
 End Function

Public Function RandCode(ByVal n As Integer) As String
  Dim arrChar As Char() = New Char() {"a"c, "b"c, "d"c, "c"c, "e"c, "f"c, _
           "g"c, "h"c, "i"c, "j"c, "k"c, "l"c, _
           "m"c, "n"c, "p"c, "r"c, "q"c, "s"c, _
           "t"c, "u"c, "v"c, "w"c, "z"c, "y"c, _
           "x"c, "0"c, "1"c, "2"c, "3"c, "4"c, _
           "5"c, "6"c, "7"c, "8"c, "9"c, "A"c, _
           "B"c, "C"c, "D"c, "E"c, "F"c, "G"c, _
           "H"c, "I"c, "J"c, "K"c, "L"c, "M"c, _
           "N"c, "Q"c, "P"c, "R"c, "T"c, "S"c, _
           "V"c, "U"c, "W"c, "X"c, "Y"c, "Z"c}
  Dim num As New StringBuilder()
  Dim rnd As New Random(DateTime.Now.Millisecond)
  For i As Integer = 0 To n - 1
   num.Append(arrChar(rnd.[Next](0, arrChar.Length)).ToString())
  Next
  Return num.ToString()
 End Function

Public Function RandCode(ByVal n As Integer) As String
  Dim arrChar As Char() = New Char() {"a"c, "b"c, "d"c, "c"c, "e"c, "f"c, _
           "g"c, "h"c, "i"c, "j"c, "k"c, "l"c, _
           "m"c, "n"c, "p"c, "r"c, "q"c, "s"c, _
           "t"c, "u"c, "v"c, "w"c, "z"c, "y"c, _
           "x"c, "0"c, "1"c, "2"c, "3"c, "4"c, _
           "5"c, "6"c, "7"c, "8"c, "9"c, "A"c, _
           "B"c, "C"c, "D"c, "E"c, "F"c, "G"c, _
           "H"c, "I"c, "J"c, "K"c, "L"c, "M"c, _
           "N"c, "Q"c, "P"c, "R"c, "T"c, "S"c, _
           "V"c, "U"c, "W"c, "X"c, "Y"c, "Z"c}
  Dim num As New StringBuilder()
  Dim rnd As New Random(DateTime.Now.Millisecond)
  For i As Integer = 0 To n - 1
   num.Append(arrChar(rnd.[Next](0, arrChar.Length)).ToString())
  Next
  Return num.ToString()
 End Function

Function makeRand(ByVal maxLen As Integer) As String '生成签名时用随机串
  Dim strNewPass As String = vbNullString
  Dim lower As Long
  Dim whatsNext As Long
  Dim upper As Long
  Dim intCounter As Long
  Randomize()
  For intCounter = 1 To maxLen
   whatsNext = Int((1 - 0 + 1) * Rnd() + 0)
   If whatsNext = 0 Then
    upper = 122
    lower = 100
   Else
    upper = 57
    lower = 48
   End If
   strNewPass = strNewPass & Chr(Int((upper - lower + 1) * Rnd() + lower))
  Next
  makeRand = strNewPass
 End Function

 Dim rand As Random = New System.Random(10)‘这里10就代表是10为
  Debug.Print(rand.Next().ToString)