DoEvents
evolution; the API approach
                                                                        
If there was such a function to
inspect the message queue for user input, we would have a main benefit:
      
We would speed up our loops ‘cause we would process all the messages in
the queue (with DoEvents) only on user input. It’s faster to check for
a message than to process all messages every time. 


 API provides us with such a
function:
 It’s called
GetInputState and you can locate it in user32 library.


 Here is the declaration: 


     
Public Declare Function GetInputState Lib
"user32" () As Long 


 The GetInputState function
determines whether there are mouse-button or keyboard messages in the calling
thread's message queue.
If the queue contains one or more new mouse-button or
keyboard messages, the return value is nonzero else if there are no new
mouse-button or keyboard messages in the queue, the return value is zero. 


So we can create an improved DoEvents with a Subroutine
like this : 


Public Sub newDoEvents() 


       
If GetInputState() <> 0 then DoEvents 


End Sub 


 You
can use GetInputState() with many variations for example :            


        
uCancelMode = False 


         
       Do until rs.Eof 


                        
Rs.AddNew  


                                 
(..your source here)


                          
Rs.Update 


                          
Rs.MoveNext 


                             
If GetInputState() <> 0 then 


                                
DoEvents 


                                 
If uCancelMode Then Exit Do 


                             
End If 


      
             


                        
Loop 


                        



                   
     Msgbox “Finished.” 


 


…or
we could use it in a ScreenSaver e.t.c. 


Let’s
go a little further now and see what exactly is behind GetInputState(). 


It
is another API function located in User32 as well; GetQueueStatus() 


The GetQueueStatus function indicates the type of messages
found in the calling thread's message queue. Here are the flags that
GetQueueStatus uses : 


QS_ALLEVENTS             An
input, WM_TIMER, WM_PAINT, WM_HOTKEY, or posted message is in the queue. 


QS_ALLINPUT          
    Any
message is in the queue. 


QS_ALLPOSTMESSAGE   
A posted message (other than those listed here) is in the queue. 


QS_HOTKEY   
         
    A
WM_HOTKEY message is in the queue. 


QS_INPUT                  
 An input message is in the queue. 


QS_KEY                  
    A WM_KEYUP, WM_KEYDOWN, WM_SYSKEYUP, or WM_SYSKEYDOWN                                 
                                
 message is in the queue. 


QS_MOUSE                 
A WM_MOUSEMOVE message or mouse-button message (WM_LBUTTONUP, WM_RBUTTONDOWN,                              
    and so on). 


QS_MOUSEBUTTON      
A mouse-button message (WM_LBUTTONUP, WM_RBUTTONDOWN, and so on). 


QS_MOUSEMOVE         
A WM_MOUSEMOVE message is in the queue. 


QS_PAINT                  
A WM_PAINT message is in the queue. 


QS_POSTMESSAGE      
A posted message (other than those listed here)
is in the queue. 


QS_SENDMESSAGE      
A message sent by another thread or application
is in the queue. 


QS_TIMER                  
A WM_TIMER message is in the queue. 


 


         
(I believe that GetInputState() is a GetQueueStatus(QS_HOTKEY Or QS_KEY Or
QS_MOUSEBUTTON)) 



With these constants you can create your own
GetInputState function that fits your needs. For example you can create a custom
function that issues DoEvents when it’ll detects not only a Keyboard or Mouse

Key input, but also a WM_PAINT signal. 


Why’s that? ‘cause in your loop you might need
to update the screen so you must let your custom function process the specific
signal. 


Look at this : 


 


Public Const QS_HOTKEY = &H80 


Public Const QS_KEY = &H1 


Public Const QS_MOUSEBUTTON = &H4 


Public Const QS_MOUSEMOVE = &H2 


Public Const QS_PAINT = &H20 


Public Const QS_POSTMESSAGE = &H8 


Public Const QS_SENDMESSAGE = &H40



Public Const QS_TIMER = &H10 


Public Const QS_ALLINPUT = (QS_SENDMESSAGE
Or QS_PAINT Or QS_TIMER Or
QS_POSTMESSAGE Or                            
             
   QS_MOUSEBUTTON Or QS_MOUSEMOVE Or QS_HOTKEY Or
QS_KEY) 


Public Const QS_MOUSE = (QS_MOUSEMOVE
Or QS_MOUSEBUTTON) 


Public Const QS_INPUT = (QS_MOUSE Or
QS_KEY) 


Public Const QS_ALLEVENTS = (QS_INPUT
Or QS_POSTMESSAGE Or QS_TIMER Or
QS_PAINT Or QS_HOTKEY) 


 


Public Declare Function GetQueueStatus
Lib "user32" (ByVal qsFlags As Long) As Long 


 


 


Public Function cGetInputState() 


Dim
qsRet As Long 


qsRet = GetQueueStatus(QS_HOTKEY Or
QS_KEY Or QS_MOUSEBUTTON Or QS_PAINT) 


                  
cGetInputState = qsRet 


End Function 


 


With this function you can trigger the DoEvents to
be executed only when the message queue contains Key input, Mouse button or a
WM_PAINT signal. 


 


Call it like this…. 


. . if cGetInputState() <> 0
then DoEvents 


 


          This was
tested and proved to optimise a loop  by
100% !!!!!!!!!


 


I wrote this article believing that the API is a
powerfull part on Windows programming and deserves your attention. I was stuck
several times and API prooved to be a problem solver. API is a large world but
with little effort, you can take advantage of it. You will create more
sophisticated and user aware programs. 


 


I hope I helped.


Any comments or suggestions are always welcomed. 


        
John
Galanopoulos
          
(Below there is a link to the .doc version of this article, for you to download. 
If you want to implement this source in your projects, download the Class Module posted by http://www.planet-source-code.com/vb/scripts/ShowCode.asp?lngWId=1&txtCodeId=33401 John Baughman in this address 
Also, you can check out Olav Jordan's article : http://www.planet-source-code.com/vb/scripts/ShowCode.asp?txtCodeId=37888&lngWId=1 Optimized loop (no more doevents) 

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