Making a Trial version of a program - vb.net

Question

I am making trial version of my vb .net project but it is not counting the days , date and time .
Can u please give me any suggestions to correct it. I am using the following code
Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim intTime As Integer = 1
Dim dteLastStart, dteStartDate As Date
Dim blnFirstTime, blnEnabled As Boolean
Dim lngTimeLeft As Long
blnEnabled = True
If dteStartDate = Nothing Then
dteStartDate = Now
End If
My.Application.SaveMySettingsOnExit = True
If DateDiff(DateInterval.Day, dteLastStart, Now) < 0 Then
'First clock change
If intTime = 1 Then
MsgBox("FRED has detected that you have changed your system date to an earlier date" & vbCrLf & "As FRED has built-in security," & vbCrLf & "FRED will only run until the next intTime you change your system date", MsgBoxStyle.OkOnly Or MsgBoxStyle.Exclamation, "System Date Changed")
intTime = 2
ElseIf intTime = 2 Then
'Second clock change
blnEnabled = False
MsgBox("FRED has detected that you have changed your system date to an earlier date" & vbCrLf & "As this is the second warning, FRED will now be disabled", MsgBoxStyle.OkOnly Or MsgBoxStyle.Exclamation, "System Date Changed")
End If
'disables app
If blnEnabled = False Then
If MsgBox("FRED is disabled", MsgBoxStyle.OkOnly Or MsgBoxStyle.Information, "Disabled") = MsgBoxResult.Ok Then
For Each form As Form In My.Application.OpenForms
form.Close()
Next
End If
End If
End If
If DateDiff(DateInterval.Day, dteStartDate, Now) > 29 Then
blnEnabled = False
If blnEnabled = False Then
If MsgBox("FRED has reached the end of it's trial.", MsgBoxStyle.OkOnly Or MsgBoxStyle.Information, "Trial Ended") = MsgBoxResult.Ok Then
'Close all open forms
For Each form As Form In My.Application.OpenForms
form.Close()
Next
End If
End If
End If
dteLastStart = Now
If blnFirstTime = True Then
blnFirstTime = False
End If
'Saves variable settings
My.Settings.Save()
lngTimeLeft = 29 - (DateDiff(DateInterval.Day, dteStartDate, Now))
MsgBox("This is a 29-day trial version." & vbCrLf & "You have " & CStr(lngTimeLeft) & " days left.", MsgBoxStyle.OkOnly, "FRED Trial")
end sub
end class

Answer 1

Let's say your program called "MyProg" and you want user to try it for 7 days.
So, conceptually, you'll have entry in registry:
HKLM\SOFTWARE\MyProg
Each run of the software, you will have to check if it exists, if not, assuming it's a first run and you will create the entry and set value. If entry exists, you will retrieve value and compare to now.
No for coding, here is an example function that handles registry and returns false if date expired or true if still trial period:
Private Function HandleRegistry() As Boolean
Dim firstRunDate As Date
firstRunDate = My.Computer.Registry.GetValue("HKEY_LOCAL_MACHINE\SOFTWARE\MyProg", "FirstRun", Nothing)
If firstRunDate = Nothing Then
firstRunDate = Now
My.Computer.Registry.SetValue("HKEY_LOCAL_MACHINE\SOFTWARE\MyProg", "FirstRun", firstRunDate)
ElseIf (Now - firstRunDate).Days > 7 Then
Return False
End If
Return True
End Function
No all you have to do, is to call it and handle response:
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
Dim result As Boolean = HandleRegistry()
If result = False Then 'something went wrong
MsgBox("Trial expired")
Else
MsgBox("Trial version")
End If
End Sub
Of course this is example only, so you get the idea, but practicality i would encode date and call registry name entry something else so it won't be user friendly. Also, remember the architecture issue so you know where it's written.
Hope that helps