Update:
The solution I arrived at is a bit convoluted, but it works.
In the parent form I added timer code:
Code:
Private Sub Form_Timer()
Static counter As Integer
If IsNull(Me.txt_PrevSubFormDate) Or Me.txt_PrevSubFormDate <> Me.txt_SubFormDate Then
viewCheck
Me.txt_PrevSubFormDate = Me.txt_SubFormDate
Me.TimerInterval = 250
counter = 0
End If
counter = counter + 1
If counter = 10 Then
TimerInterval = 0
End If
End Sub
where viewcheck is checking for items to highlight.
The Me.txt_SubFormDate control source is
Code:
=[_subfrm_Courses].[Form]![txt_WhenChanged]
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In the subform for controls of interest I added After Update and Form On Delete events that included calls to whenChanged
Code:
Sub whenChanged()
Me.txt_WhenChanged = Now()
Me.Parent.TimerInterval = someNonZeroTimerSetting
End Sub
These instrumented controls in the subform will trigger a viewcheck in the parent form. The timer looping is to ensure the timer loop doesn't beat out the system's handling of the parent form's =Sum() processing.
It is definitely an ugly approach, and suffers from some telltale screen flicker, but it does get the job done.
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The short story is use Form_Timer() in the parent form to loop, doing the viewcheck, in conjunction with changes in the subform triggering the timer in the parent form.
If someone has a cleaner approach please share.