Heavy usage w/o DoEvents (the proper way)

Submitted on: 2/2/2015 6:17:00 PM
By: CR Hough (from psc cd)  
Level: Intermediate
User Rating: By 2 Users
Compatibility: VB 5.0, VB 6.0
Views: 3770
     Never use DoEvents again. This is a standard C/C++ Message Pump. Compare each of these three methods against each other (including DoEvents) and watch your CPU usage. The code is pretty self-explanatory I think.

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				  Put this in the General Declarations area for your module:
Declare Function PeekMessage Lib "user32" Alias "PeekMessageA" (lpMsg As MSG, ByVal hwnd As Long, ByVal wMsgFilterMin As Long, ByVal wMsgFilterMax As Long, ByVal wRemoveMsg As Long) As Long
Declare Function GetMessage Lib "user32" Alias "GetMessageA" (lpMsg As MSG, ByVal hwnd As Long, ByVal wMsgFilterMin As Long, ByVal wMsgFilterMax As Long) As Long
Declare Function TranslateMessage Lib "user32" (lpMsg As MSG) As Long
Declare Function DispatchMessage Lib "user32" Alias "DispatchMessageA" (lpMsg As MSG) As Long

Private Const PM_NOREMOVE = &H0
Private Const PM_REMOVE = &H1
Private Const WM_QUIT = &H12

Private Type POINTAPI
X As Long
Y As Long
End Type

Private Type MSG
hwnd As Long
Message As Long
wParam As Long
lParam As Long
time As Long
End Type

Put the following in your sub main (after setting blRunning = True):
'*** Try commenting and uncommenting each of these three ***
'*** methods. Watch your CPU usage when you run each of ***
'*** them. Then go back to using GetMessage. ***
Do While blRunning
'*** use the PeekMessage version if you want to use 100% CPU
'*** frex to do background processing that doesn't rely on
'*** windows messages
'If PeekMessage(Message, 0&, 0&, 0&, PM_REMOVE) Then
' Call TranslateMessage(Message)
' Call DispatchMessage(Message)
'End If

'*** use the GetMessage version if you only want to do
'*** processing if there's a message
If GetMessage(Message, 0&, 0&, 0&) Then
Call TranslateMessage(Message)
Call DispatchMessage(Message)
End If

'*** the 'pure vb' poor way to do this

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