Powerpoint macro - basic problem with counter - vba

Question

I am making my first Powerpoint 2007 macro and I am having a bit of trouble with it hanging, and not letting me move on to the next slide. I can press ESCAPE to quit the slideshow, but pressing space bar or anything else won't progress to the next slide. After a while, it just crashes. I come from a C++/Java background so I think its just something basic that I'm missing.
Basically I am trying to do a counter slide that counts the days/minutes/seconds from a particular date. When the slide loads I want it to show, in real time, how long its been since that date. I've put it through an infinite loop, which works fine to update the time, but then doesnt let me move on to the next slide.
Here's my code:
Sub OnSlideShowPageChange(ByVal SSW As SlideShowWindow)
'If SSW.View.CurrentShowPosition = 3 Then
Do While SSW.View.CurrentShowPosition = 3 ' infinite loop
Dim currentSlide As Integer
currentSlide = SSW.View.CurrentShowPosition
Dim startDate As Date
Dim currentDate As Date
Dim sngDiff As Single
Dim lngDays As Long
Dim lngHours As Long
Dim lngMinutes As Long
Dim lngSeconds As Long
startDate = #7/22/2011 2:00:00 PM#
currentDate = Now
sngDiff = currentDate - startDate
lngDays = CLng(sngDiff)
sngDiff = sngDiff - lngDays
lngHours = Hour(sngDiff)
lngMinutes = Minute(sngDiff)
lngSeconds = Second(sngDiff)
With ActivePresentation.Slides(currentSlide)
With .Shapes(2)
.TextFrame.TextRange.Text = "It has been:" & lngDays & " Days " & lngHours & " hours " & lngMinutes & " minutes " & lngSeconds & " Seconds"
End With
End With
DoEvents
Loop
End Sub
Do I need to listen for some sort of button click to stop this infinite loop, or how do I do this?
Thanks.

Answer 1

A user form is something you add in the VBA editor; it's what you'd normally think of as a dialog box, though forms can be used for other things and needn't even become visible; that's what we're going to do here:
Option Explicit
Public bFormCodeRunning As Boolean
Sub FormDemo()
' Set a flag to let us know the code in the form
' is running
bFormCodeRunning = True
' "show" the form
UserForm1.Show vbModeless
End Sub
Sub KillForm()
' call this at some other point in the presentation
' when you're sure you're done running the form code
If Not bFormCodeRunning Then
Unload UserForm1
End If
' You could actually call this from your slide change event handler
End Sub
Then Insert, User Form from the menu to add a new form; doubleclick it to view its code and add this:
Private Sub UserForm_Activate()
' Don't show my face
Me.hide
DoEvents
' prove that the form's loaded
MsgBox "I'm well-formed"
DoEvents
' and put your other code here
' and when the code's done, flag it
bFormCodeRunning = False
End Sub

Answer 2

For doing a time delay in a VBA context it is usually better to use a form_timer object so in your code have:
If SSW.View.CurrentShowPosition = 3 Then
Me.TimerInterval = 1000
Else
Me.TimerInterval = 0
End If
Or something similar. Then in the form timer code have your clock update code
Private Sub Form_Timer()
// Your clock update code here
End Sub
It's been years since I've done any VBA so I'm a bit rusty but I hope this helps. In general use timers instead of loops for threading tasks, VBA doesn't cope well with them.

Answer 3

The problem is that your routine "owns" the app; until it exits, you won't be able to do anything manually (ie, advance to the next slide).
Whether or not you use a timer on a form (and fwiw, the Timer control isn't shipped with VBA as it is with VB), I think a form may be your solution.
Have your event handler load a form modelessly then exit.
The code in the form can then do any mods to slides or whatever else you want.
Include DoEvents often enough that you don't slow down the main app, but the code in the form will run independently of what the main app is doing.
You don't need to make the form visible (and probably don't want to).