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| Title | Make a program that has no forms but that uses API timers |
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| Description | If a program doesn't have any forms, it cannot use a Timer control. This example shows how to make a program without any forms that uses API timers in Visual Basic 6. |
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| Keywords | Timer, Timer control, time, speed, performance |
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| Categories | Controls, API |
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The trick is to keep Sub Main running until the program is ready to exit. The program starts an API timer and then enters a DoEvents loop. When the variable m_Running is False, the program ends the loop, kills the timer, and exits.
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Private m_TimerID As Long
Private m_Running As Boolean
Private Sub Main()
' Start the timer.
m_TimerID = SetTimer(0, 0, 3000, _
AddressOf MyTimer)
' Run until the timer sets m_Running to False.
m_Running = True
Do While m_Running
DoEvents
Loop
' Stop the timer.
KillTimer 0, m_TimerID
End Sub
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When the timer fires, the program asks the user if it should continue. If it should not, the program sets m_Running to False.
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' See if the user wants to stop.
Public Sub MyTimer(hwnd As Long, msg As Long, idTimer As _
Long, dwTime As Long)
Static i As Integer
Static messagebox_visible As Boolean
' Do nothing if another timer event is currently
' displaying the message box.
If messagebox_visible Then Exit Sub
messagebox_visible = True
i = i + 1
If MsgBox(i & ": Stop?", vbYesNo) = vbYes Then _
m_Running = False
messagebox_visible = False
End Sub
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NOTE: Stefan De Prins has these notes:
Allthough your technique works fine, you should take a look at the cpu usage when you do this. I once had to write a program that had to check wether Oracle was finshed indexing files before doing anyhting. I used the same technique (in Sub Main use doevents in a while loop and in my timer event check for the indexing every five minutes), the cpu usage went skyhigh). Therefore I had to use a form (which I know isn't what this example is about), and only start my actual code when in the timer event I could, that way the cpu usage stayed down untill I had to really start my actual code, and I do think this is essential on a server process, especially in my case where the actual code only took seconds, but I could have to wait maybe an hour before the Oracle indexing was finished, meaning I would be using the full server cpu time for that entire timespan. In short, be carefull when you use DoEvents. Many people still use it as a way to "kinda" make VB multi-threaded and believe me, VB isn't multithreaded !! ;-)
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