Exactly WHAT is accomplished with "DO EVENTS"?

[Lauren Wilson]

Hello group,

Somehow, I have not yet fully understood the meaning and purpose of
"DoEvents". Can someone post or point me to a clear, concise
explanation of it -- one that includes situational examples of how and
why it is used? The Access on-line help is not as helpful as I need
for my mental density!

Sorry to be so dense. Please indulge me.

Thanks,

--LW

[David Schofield]

On Wed, 29 Sep 2004 09:00:08 -0500, Lauren Wilson <???@???.???> wrote:

Hello group,

Somehow, I have not yet fully understood the meaning and purpose of
"DoEvents". Can someone post or point me to a clear, concise
explanation of it -- one that includes situational examples of how and
why it is used? The Access on-line help is not as helpful as I need
for my mental density!

Sorry to be so dense. Please indulge me.

Thanks,

--LW

Hi
Good question. I suspect it dates from Windows 3.1 before preemptive
scheduling. According to the help file for Access 97 (which had a
useful one) it "Yields execution so that the operating system can
process other events." If so it is now redundant.

(Though Access traditionally hogs processor cycles it does give way
when other processes nee them)

Over the years I have often stuck it in when things seem to be going
wrong in the timing sense but it's never made the slightest
difference,
David Schofield

[Arno R]

From the Access Cookbook (Getz-Litwin-Baron):
"Sometimes Access seems to come to a halt... Effective use of DoEvents can make the difference ..."

Make a testform with a button cmdDoEvents and a label lblGrow (backgroundcolor as you like)
Code:
Private Sub cmdDoEvents_Click()
Dim intI As Integer
Me!lblGrow.Width = 500
For intI = 0 To 2500 Step 1
Me!lblGrow.Width = Me!lblGrow.Width + 1
'Me.Repaint
DoEvents
Next intI
End Sub

Try to push the button with and without the line DoEvents
(Without DoEvents use Me.Repaint to see the screen repaint).

The difference is when for instance you try to move the form.
-- When you don't use DoEvents you can't move the form WILE the code is running.
Your 'movement' (or other mouseclicks) will be executed AFTER the code is finished.
--When you use DoEvents you can smoothly move the form (code waits until you are done)

Sometimes this can make the difference indeed ...

HTH
Arno R

"Lauren Wilson" <???@???.???> schreef in bericht news:hn********************************@4ax.com...

Hello group,

Somehow, I have not yet fully understood the meaning and purpose of
"DoEvents". Can someone post or point me to a clear, concise
explanation of it -- one that includes situational examples of how and
why it is used? The Access on-line help is not as helpful as I need
for my mental density!

Sorry to be so dense. Please indulge me.

Thanks,

--LW

[Trevor Best]

Lauren Wilson wrote:

Hello group,

Somehow, I have not yet fully understood the meaning and purpose of
"DoEvents". Can someone post or point me to a clear, concise
explanation of it -- one that includes situational examples of how and
why it is used? The Access on-line help is not as helpful as I need
for my mental density!

David nailed it (almost) for giving up CPU time to other apps in Windows
3.x but additionaly and more importantly nowadays, it allows other
events within the same application to run, e.g. Timer events, Mouse
Click and keypress events, repainting, etc. try this on a command button
(with the caption set to "Start":

(air code)
Sub cmdStart_Click()
Static sfRunning As Boolean
Dim l As Long
With cmdStart
if sfRunning then
.Caption = "Start"
sfRunning=False
else
.Caption = "Stop"
sfRunning = True
Do while sfRunning
l = l + 1
Me!txtTextBox.Value = l
DoEvents
Loop
End With
End Sub

Press the Start button and watch the textbox (txtTextBox) count up fast,
press same button (now labelled "Stop") to stop it.

Now take Doevents out, you won't see the caption on the button change or
the textbox count up, neither will you be able to stop it (unless you
Ctrl+Break)

--

\\\\\\
\\ \\ Windows is searching
\ \ For your sig.
\ \ Please Wait.
\__\

[David Schofield]

Thanks!
David

[Lauren Wilson]

Awesome! Thanks Arno.
On Wed, 29 Sep 2004 20:44:56 +0200, "Arno R"
<ar****************@tiscali.nl> wrote:

From the Access Cookbook (Getz-Litwin-Baron):
"Sometimes Access seems to come to a halt... Effective use of DoEvents can make the difference ..."

Make a testform with a button cmdDoEvents and a label lblGrow (backgroundcolor as you like)
Code:
Private Sub cmdDoEvents_Click()
Dim intI As Integer
Me!lblGrow.Width = 500
For intI = 0 To 2500 Step 1
Me!lblGrow.Width = Me!lblGrow.Width + 1
'Me.Repaint
DoEvents
Next intI
End Sub

Try to push the button with and without the line DoEvents
(Without DoEvents use Me.Repaint to see the screen repaint).

The difference is when for instance you try to move the form.
-- When you don't use DoEvents you can't move the form WILE the code is running.
Your 'movement' (or other mouseclicks) will be executed AFTER the code is finished.
--When you use DoEvents you can smoothly move the form (code waits until you are done)

Sometimes this can make the difference indeed ...

HTH
Arno R

"Lauren Wilson" <???@???.???> schreef in bericht news:hn********************************@4ax.com...

Hello group,

Somehow, I have not yet fully understood the meaning and purpose of
"DoEvents". Can someone post or point me to a clear, concise
explanation of it -- one that includes situational examples of how and
why it is used? The Access on-line help is not as helpful as I need
for my mental density!

Sorry to be so dense. Please indulge me.

Thanks,

--LW

[Lauren Wilson]

Thanks Trevor. You are one of the reasons I come to this group. Your
tireless contributions are much appreciated.

On Wed, 29 Sep 2004 20:24:20 +0100, Trevor Best <nospam@localhost>
wrote:

Lauren Wilson wrote:

Hello group,

Somehow, I have not yet fully understood the meaning and purpose of
"DoEvents". Can someone post or point me to a clear, concise
explanation of it -- one that includes situational examples of how and
why it is used? The Access on-line help is not as helpful as I need
for my mental density!

David nailed it (almost) for giving up CPU time to other apps in Windows
3.x but additionaly and more importantly nowadays, it allows other
events within the same application to run, e.g. Timer events, Mouse
Click and keypress events, repainting, etc. try this on a command button
(with the caption set to "Start":

(air code)
Sub cmdStart_Click()
Static sfRunning As Boolean
Dim l As Long
With cmdStart
if sfRunning then
.Caption = "Start"
sfRunning=False
else
.Caption = "Stop"
sfRunning = True
Do while sfRunning
l = l + 1
Me!txtTextBox.Value = l
DoEvents
Loop
End With
End Sub

Press the Start button and watch the textbox (txtTextBox) count up fast,
press same button (now labelled "Stop") to stop it.

Now take Doevents out, you won't see the caption on the button change or
the textbox count up, neither will you be able to stop it (unless you
Ctrl+Break)