How to get VBA Macro to run continuously in the background? - vba

Question

I want to monitor a value and get an email notifications when certain conditions are met. I have a macro like so:
Do While True
Worksheet.Calculate
If Value > 10 Then
SendEmail
End If
Sleep 60*CLng(1000)
Loop
However, when I run this, it clogs up the entire program and will turn unresponsive if I try to do anything.
Is there anyway to accomplish this but have it run in the background or at least not crash the program?
What I was doing before was using VBScript to open a not-visible spreadsheet and the VBScript ran continuously in the background monitoring the condition and worked fine, but my client really wants a GUI and for it to be in the program itself.
Any thoughts?

Answer 1

Use the Application.OnTime method to schedule code that will run in one minute.
Your code will look something like this (Untested):
Sub CreateNewSchedule()
Application.OnTime EarliestTime:=DateAdd("n", 1, Now), Procedure:="macro_name", Schedule:=True
End Sub
Sub macro_name()
If Value > 10 Then
SendEmail
Else
CreateNewSchedule
End If
End Sub
You might want to store the time of the next schedule in a global variable so that the Workbook_BeforeClose event can cancel the next schedule. Otherwise Excel will re-open the workbook.
Public nextScheduledTime As Date
Sub CreateNewSchedule()
nextScheduledTime = DateAdd("n", 1, Now)
Application.OnTime EarliestTime:=nextScheduledTime , Procedure:="macro_name", Schedule:=True
End Sub
Sub macro_name()
If Value > 10 Then
SendEmail
Else
CreateNewSchedule
End If
End Sub
Private Sub Workbook_BeforeClose(Cancel As Boolean)
On Error Resume Next
Application.OnTime EarliestTime:=nextScheduledTime, Procedure:="macro_name", Schedule:=False
End Sub
You can then continue to use Excel between the scheduled times.

Answer 2

I think you need to specifically process the application event stack with a DoEvents call. This allows user interactions with the spreadsheet to occur, where normally the macro would take precedence. You code would look something like:
Do While True
If Value > 10 Then
SendEmail
End If
Sleep 60*CLng(1000)
DoEvents
Loop
You could also construct a GUI with HTA if you wanted to remain with VBScript.