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| Title | Make a program with no forms that uses API timers and Sleep |
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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. It uses the Sleep API function to minimize CPU use while waiting for events. |
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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 loop where it sleeps for a while and then calls DoEvents. When the variable m_Running is False, the program ends the loop, kills the timer, and exits.
In some simple tests, a similar program without Sleep used more than 90 percent of the CPU but this version used only about 30 percent.
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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
' Pause a little while so we don't hog the CPU.
Sleep 200
DoEvents
Loop
' Stop the timer.
KillTimer 0, m_TimerID
End Sub
' 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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