请问老师，如何设置注册码的有效期！假如一个月到期了，注册码就失效了，需要重新注册！望老师赐教

 把到期日期写入注册码里面，如

dim str as string = computerId
Dim zcm As String = EncryptText(str & "|" & new Date(2016,9,1), "abc", "abc")
output.show(zcm)

\'-----------------------

Dim s As String = DecryptText(zcm, "abc", "abc")
output.show(s)
msgbox(s.split("|")(1))

Dim n As Integer = Registry.GetValue("HKEY_CURRENT_USER\\Software\\MyApp","Count",1)
Dim Code As String =Registry.GetValue("HKEY_CURRENT_USER\\Software\\MyApp","Register" & ComputerId,"")
Dim Ok As Boolean
If Code > "" AndAlso DecryptText(Code,"abc","abc") = ComputerId Then \'如果注册码正确
    OK = True
Else
    If n > 5 Then
        Forms("注册码").Open()
        Code = Registry.GetValue("HKEY_CURRENT_USER\\Software\\MyApp","Register" & ComputerId,"")
        If Code > "" AndAlso DecryptText(Code,"abc","abc") = ComputerId Then \'如果注册码正确
            OK = True
        End If
    End If
    If n > 20 AndAlso Ok = False Then
        Messagebox.Show("您正在使用的产品已经超出试用次数!")
        Syscmd.Project.Exit()
    End If
End If
Registry.SetValue("HKEY_CURRENT_USER\\Software\\MyApp","count",n + 1)

dim str as string = computerId
Dim zcm As String = EncryptText(str & "|" & new Date(2016,9,1), "abc", "abc")
output.show(zcm)

Dim s As String = DecryptText(zcm, "abc", "abc")
output.show(s)
msgbox(s.split("|")(1))

这样改了 没有效果啊 ！本人小白，望老师不宁赐教！谢谢

Dim n As Integer = Registry.GetValue("HKEY_CURRENT_USER\\Software\\MyApp","Count",1)
Dim Code As String =Registry.GetValue("HKEY_CURRENT_USER\\Software\\MyApp","Register" & ComputerId,"")
Dim Ok As Boolean

If Code > ""  Then \'如果注册码正确
    Dim str As String = DecryptText(Code,"abc","abc")
    Dim ary() As String = str.Split(",")
    If ary.length = 2 AndAlso ary(1) >= Date.Now AndAlso ary(0) = ComputerId Then
        OK = True
    End If
End If
If ok = False Then
    If n > 5 Then
        Forms("注册码").Open()
        Code = Registry.GetValue("HKEY_CURRENT_USER\\Software\\MyApp","Register" & ComputerId,"")
        If Code > "" AndAlso DecryptText(Code,"abc","abc") = ComputerId Then \'如果注册码正确
            OK = True
        End If
    End If
    If n > 20 AndAlso Ok = False Then
        Messagebox.Show("您正在使用的产品已经超出试用次数!")
        Syscmd.Project.Exit()
    End If
End If
Registry.SetValue("HKEY_CURRENT_USER\\Software\\MyApp","count",n + 1)