Functions won't calculate without F2

[Guest]

Good morning all!

I wrote a simple function to calculate the values of all hidden cells in a
range.
It works fine, except that I have to edit the formula with [F2] and [Enter]
before it displays the correct answer - otherwise, it just displays the
result of the previous calculation.

Can anyone help, please?

Thanks in advance

Pete

Function SumHiddenRows(TheHiddenRange)
Dim HiddenTotal As Long
Dim HiddenCell As Range

HiddenTotal = 0
For Each HiddenCell In TheHiddenRange
If HiddenCell.EntireRow.Hidden = True Then
HiddenTotal = HiddenTotal + HiddenCell.Value
End If
Next
SumHiddenRows = HiddenTotal
Calculate
End Function

 

[Niek Otten]

Hi Peter,

If you change the value of any of the cells in the hidden range, the
function should recalculate, unless you happen to have Manual calculation
switched on (Tools>Options, Calculation tab).
But changing a cell form visible to hidden does not trigger a recalculation,
not even if you include Application.Volatile.
You could force a recalc by including a volatile function in the formula,
like in

=SumHiddenRows(A1:A10)+(now()*0)

--
Kind regards,

Niek Otten

Microsoft MVP - Excel

 

[Guest]

Hmm. Perhaps I should have been a little more specific with the problem.

I have a range of cells containing the numbers 1-10, with 4 buttons that run
macros to hide/unhide the rows containg the odd or even numbers.

It's when I run these macros to hide 1/3/5/7/8 (displaying 2/4/6/8/10) or
hide 2/4/6/8/10 (displaying 1/3/5/7/9) that the function doesn't recalculate.

There is a SumVisibleRows function too that does the opposite of
SumHiddenRows, displaying a total for all the visible cells in the range thus:

Function SumVisibleRows(TheVisibleRange)
Dim VisibleTotal As Long
Dim VisibleCell As Range

VisibleTotal = 0
For Each VisibleCell In TheVisibleRange
If VisibleCell.EntireRow.Hidden = False Then
VisibleTotal = VisibleTotal + VisibleCell.Value
End If
Next
SumVisibleRows = VisibleTotal
Calculate
End Function

If I change the value of a visible cell in the list, SumVisibleCells
correctly calculates the new value without F2, but neither formula calculates
new totals on its own when the hide/unhide macros are run.

Should this be some sort of Worksheet_Change macro instead, and if so, can
anyone advise on the syntax for picking up changes to the hidden property of
a row?

Thanks again

Pete

 

[Niek Otten]

I'm afraid even that won't work. You'll have to include a dummy argument and
supply NOW() as value to get the function recalculated

--
Kind regards,

Niek Otten

Microsoft MVP - Excel

Hi Peter,

If you change the value of any of the cells in the hidden range, the
function should recalculate, unless you happen to have Manual calculation
switched on (Tools>Options, Calculation tab).
But changing a cell form visible to hidden does not trigger a
recalculation, not even if you include Application.Volatile.
You could force a recalc by including a volatile function in the formula,
like in

=SumHiddenRows(A1:A10)+(now()*0)

--
Kind regards,

Niek Otten

Microsoft MVP - Excel

Good morning all!

I wrote a simple function to calculate the values of all hidden cells in
a
range.
It works fine, except that I have to edit the formula with [F2] and
[Enter]
before it displays the correct answer - otherwise, it just displays the
result of the previous calculation.

Can anyone help, please?

Thanks in advance

Pete

Function SumHiddenRows(TheHiddenRange)
Dim HiddenTotal As Long
Dim HiddenCell As Range

HiddenTotal = 0
For Each HiddenCell In TheHiddenRange
If HiddenCell.EntireRow.Hidden = True Then
HiddenTotal = HiddenTotal + HiddenCell.Value
End If
Next
SumHiddenRows = HiddenTotal
Calculate
End Function

 

[Guest]

Thanks for giving it a go, anyway, Niek!

Pete

I'm afraid even that won't work. You'll have to include a dummy argument and
supply NOW() as value to get the function recalculated

--
Kind regards,

Niek Otten

Microsoft MVP - Excel

Hi Peter,

If you change the value of any of the cells in the hidden range, the
function should recalculate, unless you happen to have Manual calculation
switched on (Tools>Options, Calculation tab).
But changing a cell form visible to hidden does not trigger a
recalculation, not even if you include Application.Volatile.
You could force a recalc by including a volatile function in the formula,
like in

=SumHiddenRows(A1:A10)+(now()*0)

--
Kind regards,

Niek Otten

Microsoft MVP - Excel

Good morning all!

I wrote a simple function to calculate the values of all hidden cells in
a
range.
It works fine, except that I have to edit the formula with [F2] and
[Enter]
before it displays the correct answer - otherwise, it just displays the
result of the previous calculation.

Can anyone help, please?

Thanks in advance

Pete

Function SumHiddenRows(TheHiddenRange)
Dim HiddenTotal As Long
Dim HiddenCell As Range

HiddenTotal = 0
For Each HiddenCell In TheHiddenRange
If HiddenCell.EntireRow.Hidden = True Then
HiddenTotal = HiddenTotal + HiddenCell.Value
End If
Next
SumHiddenRows = HiddenTotal
Calculate
End Function

 

[Guest]

Niek,

I found a cheat.

In each of my Hide/Unhide Odd/Enen Numbers, I called a macro that simply put
the formulae back into the cells again thus:

Sub RedoFormulae()
Range("HiddenTotal").FormulaR1C1 = "=sumhiddenrows(NumberRange)"
Range("VisibleTotal").FormulaR1C1 = "=sumvisiblerows(NumberRange)"
End Sub

It's the equivalent of pressing F2 in each of the cells calling the functions.

Cheers

Pete

I'm afraid even that won't work. You'll have to include a dummy argument and
supply NOW() as value to get the function recalculated

--
Kind regards,

Niek Otten

Microsoft MVP - Excel

Hi Peter,

If you change the value of any of the cells in the hidden range, the
function should recalculate, unless you happen to have Manual calculation
switched on (Tools>Options, Calculation tab).
But changing a cell form visible to hidden does not trigger a
recalculation, not even if you include Application.Volatile.
You could force a recalc by including a volatile function in the formula,
like in

=SumHiddenRows(A1:A10)+(now()*0)

--
Kind regards,

Niek Otten

Microsoft MVP - Excel

Good morning all!

I wrote a simple function to calculate the values of all hidden cells in
a
range.
It works fine, except that I have to edit the formula with [F2] and
[Enter]
before it displays the correct answer - otherwise, it just displays the
result of the previous calculation.

Can anyone help, please?

Thanks in advance

Pete

Function SumHiddenRows(TheHiddenRange)
Dim HiddenTotal As Long
Dim HiddenCell As Range

HiddenTotal = 0
For Each HiddenCell In TheHiddenRange
If HiddenCell.EntireRow.Hidden = True Then
HiddenTotal = HiddenTotal + HiddenCell.Value
End If
Next
SumHiddenRows = HiddenTotal
Calculate
End Function

 

[Dave Peterson]

You could add:

application.volatile

At the top of your sub, but that just means that the function will calculate the
next time excel calculates. (and I'd remove the calculate from your UDF--I bet
it doesn't help!)

But hiding a row doesn't force calculation (until you get to xl2003). Maybe you
can add an "application.calculate" to the routine that hides the rows???

(In xl2003, =subtotal() has been enhanced to be able to ignore manually hidden
rows: =subtotal(109,a1:a22)

(100 + # means to ignore the manually hidden row.)

Hmm. Perhaps I should have been a little more specific with the problem.

I have a range of cells containing the numbers 1-10, with 4 buttons that run
macros to hide/unhide the rows containg the odd or even numbers.

It's when I run these macros to hide 1/3/5/7/8 (displaying 2/4/6/8/10) or
hide 2/4/6/8/10 (displaying 1/3/5/7/9) that the function doesn't recalculate.

There is a SumVisibleRows function too that does the opposite of
SumHiddenRows, displaying a total for all the visible cells in the range thus:

Function SumVisibleRows(TheVisibleRange)
Dim VisibleTotal As Long
Dim VisibleCell As Range

VisibleTotal = 0
For Each VisibleCell In TheVisibleRange
If VisibleCell.EntireRow.Hidden = False Then
VisibleTotal = VisibleTotal + VisibleCell.Value
End If
Next
SumVisibleRows = VisibleTotal
Calculate
End Function

If I change the value of a visible cell in the list, SumVisibleCells
correctly calculates the new value without F2, but neither formula calculates
new totals on its own when the hide/unhide macros are run.

Should this be some sort of Worksheet_Change macro instead, and if so, can
anyone advise on the syntax for picking up changes to the hidden property of
a row?

Thanks again

Pete

Good morning all!

I wrote a simple function to calculate the values of all hidden cells in a
range.
It works fine, except that I have to edit the formula with [F2] and [Enter]
before it displays the correct answer - otherwise, it just displays the
result of the previous calculation.

Can anyone help, please?

Thanks in advance

Pete

Function SumHiddenRows(TheHiddenRange)
Dim HiddenTotal As Long
Dim HiddenCell As Range

HiddenTotal = 0
For Each HiddenCell In TheHiddenRange
If HiddenCell.EntireRow.Hidden = True Then
HiddenTotal = HiddenTotal + HiddenCell.Value
End If
Next
SumHiddenRows = HiddenTotal
Calculate
End Function

 

[Guest]

Dave,

I modified my hide/unhide formulae to re-enter the custom functions into
their appropriate cells and it works OK. Can't wait for my Office XP upgrade!


Thanks

Pete

You could add:

application.volatile

At the top of your sub, but that just means that the function will calculate the
next time excel calculates. (and I'd remove the calculate from your UDF--I bet
it doesn't help!)

But hiding a row doesn't force calculation (until you get to xl2003). Maybe you
can add an "application.calculate" to the routine that hides the rows???

(In xl2003, =subtotal() has been enhanced to be able to ignore manually hidden
rows: =subtotal(109,a1:a22)

(100 + # means to ignore the manually hidden row.)

Hmm. Perhaps I should have been a little more specific with the problem.

I have a range of cells containing the numbers 1-10, with 4 buttons that run
macros to hide/unhide the rows containg the odd or even numbers.

It's when I run these macros to hide 1/3/5/7/8 (displaying 2/4/6/8/10) or
hide 2/4/6/8/10 (displaying 1/3/5/7/9) that the function doesn't recalculate.

There is a SumVisibleRows function too that does the opposite of
SumHiddenRows, displaying a total for all the visible cells in the range thus:

Function SumVisibleRows(TheVisibleRange)
Dim VisibleTotal As Long
Dim VisibleCell As Range

VisibleTotal = 0
For Each VisibleCell In TheVisibleRange
If VisibleCell.EntireRow.Hidden = False Then
VisibleTotal = VisibleTotal + VisibleCell.Value
End If
Next
SumVisibleRows = VisibleTotal
Calculate
End Function

If I change the value of a visible cell in the list, SumVisibleCells
correctly calculates the new value without F2, but neither formula calculates
new totals on its own when the hide/unhide macros are run.

Should this be some sort of Worksheet_Change macro instead, and if so, can
anyone advise on the syntax for picking up changes to the hidden property of
a row?

Thanks again

Pete

Good morning all!

I wrote a simple function to calculate the values of all hidden cells in a
range.
It works fine, except that I have to edit the formula with [F2] and [Enter]
before it displays the correct answer - otherwise, it just displays the
result of the previous calculation.

Can anyone help, please?

Thanks in advance

Pete

Function SumHiddenRows(TheHiddenRange)
Dim HiddenTotal As Long
Dim HiddenCell As Range

HiddenTotal = 0
For Each HiddenCell In TheHiddenRange
If HiddenCell.EntireRow.Hidden = True Then
HiddenTotal = HiddenTotal + HiddenCell.Value
End If
Next
SumHiddenRows = HiddenTotal
Calculate
End Function

 

[Dave Peterson]

I saw that in your other post.

I think I would have just recalculated in the subroutine that hid/unhid the
rows.

Dave,

I modified my hide/unhide formulae to re-enter the custom functions into
their appropriate cells and it works OK. Can't wait for my Office XP upgrade!


Thanks

Pete

You could add:

application.volatile

At the top of your sub, but that just means that the function will calculate the
next time excel calculates. (and I'd remove the calculate from your UDF--I bet
it doesn't help!)

But hiding a row doesn't force calculation (until you get to xl2003). Maybe you
can add an "application.calculate" to the routine that hides the rows???

(In xl2003, =subtotal() has been enhanced to be able to ignore manually hidden
rows: =subtotal(109,a1:a22)

(100 + # means to ignore the manually hidden row.)

Hmm. Perhaps I should have been a little more specific with the problem.

I have a range of cells containing the numbers 1-10, with 4 buttons that run
macros to hide/unhide the rows containg the odd or even numbers.

It's when I run these macros to hide 1/3/5/7/8 (displaying 2/4/6/8/10) or
hide 2/4/6/8/10 (displaying 1/3/5/7/9) that the function doesn't recalculate.

There is a SumVisibleRows function too that does the opposite of
SumHiddenRows, displaying a total for all the visible cells in the range thus:

Function SumVisibleRows(TheVisibleRange)
Dim VisibleTotal As Long
Dim VisibleCell As Range

VisibleTotal = 0
For Each VisibleCell In TheVisibleRange
If VisibleCell.EntireRow.Hidden = False Then
VisibleTotal = VisibleTotal + VisibleCell.Value
End If
Next
SumVisibleRows = VisibleTotal
Calculate
End Function

If I change the value of a visible cell in the list, SumVisibleCells
correctly calculates the new value without F2, but neither formula calculates
new totals on its own when the hide/unhide macros are run.

Should this be some sort of Worksheet_Change macro instead, and if so, can
anyone advise on the syntax for picking up changes to the hidden property of
a row?

Thanks again

Pete

:

Good morning all!

I wrote a simple function to calculate the values of all hidden cells in a
range.
It works fine, except that I have to edit the formula with [F2] and [Enter]
before it displays the correct answer - otherwise, it just displays the
result of the previous calculation.

Can anyone help, please?

Thanks in advance

Pete

Function SumHiddenRows(TheHiddenRange)
Dim HiddenTotal As Long
Dim HiddenCell As Range

HiddenTotal = 0
For Each HiddenCell In TheHiddenRange
If HiddenCell.EntireRow.Hidden = True Then
HiddenTotal = HiddenTotal + HiddenCell.Value
End If
Next
SumHiddenRows = HiddenTotal
Calculate
End Function

 

[Guest]

Dave,

I did and it doesn't work - whether you put the calculate command in the
function or the hide/unhide macros. It doesn't even work if you press F9 to
recalculate manually. You have to F2/Enter the cells containing the functions
(or, in VBA, re-enter the formulae)

Puzzling, isn't it?

Pete

I saw that in your other post.

I think I would have just recalculated in the subroutine that hid/unhid the
rows.

Dave,

I modified my hide/unhide formulae to re-enter the custom functions into
their appropriate cells and it works OK. Can't wait for my Office XP upgrade!


Thanks

Pete

You could add:

application.volatile

At the top of your sub, but that just means that the function will calculate the
next time excel calculates. (and I'd remove the calculate from your UDF--I bet
it doesn't help!)

But hiding a row doesn't force calculation (until you get to xl2003). Maybe you
can add an "application.calculate" to the routine that hides the rows???

(In xl2003, =subtotal() has been enhanced to be able to ignore manually hidden
rows: =subtotal(109,a1:a22)

(100 + # means to ignore the manually hidden row.)

Peter Rooney wrote:

Hmm. Perhaps I should have been a little more specific with the problem.

I have a range of cells containing the numbers 1-10, with 4 buttons that run
macros to hide/unhide the rows containg the odd or even numbers.

It's when I run these macros to hide 1/3/5/7/8 (displaying 2/4/6/8/10) or
hide 2/4/6/8/10 (displaying 1/3/5/7/9) that the function doesn't recalculate.

There is a SumVisibleRows function too that does the opposite of
SumHiddenRows, displaying a total for all the visible cells in the range thus:

Function SumVisibleRows(TheVisibleRange)
Dim VisibleTotal As Long
Dim VisibleCell As Range

VisibleTotal = 0
For Each VisibleCell In TheVisibleRange
If VisibleCell.EntireRow.Hidden = False Then
VisibleTotal = VisibleTotal + VisibleCell.Value
End If
Next
SumVisibleRows = VisibleTotal
Calculate
End Function

If I change the value of a visible cell in the list, SumVisibleCells
correctly calculates the new value without F2, but neither formula calculates
new totals on its own when the hide/unhide macros are run.

Should this be some sort of Worksheet_Change macro instead, and if so, can
anyone advise on the syntax for picking up changes to the hidden property of
a row?

Thanks again

Pete

:

Good morning all!

I wrote a simple function to calculate the values of all hidden cells in a
range.
It works fine, except that I have to edit the formula with [F2] and [Enter]
before it displays the correct answer - otherwise, it just displays the
result of the previous calculation.

Can anyone help, please?

Thanks in advance

Pete

Function SumHiddenRows(TheHiddenRange)
Dim HiddenTotal As Long
Dim HiddenCell As Range

HiddenTotal = 0
For Each HiddenCell In TheHiddenRange
If HiddenCell.EntireRow.Hidden = True Then
HiddenTotal = HiddenTotal + HiddenCell.Value
End If
Next
SumHiddenRows = HiddenTotal
Calculate
End Function

 

[David Welch]

Thats right, this is the behaviour under Excel 2000 and below, but not
Excel 2002 and greater. Your macro works under Excel 2003.

Dave,

I did and it doesn't work - whether you put the calculate command in the
function or the hide/unhide macros. It doesn't even work if you press F9 to
recalculate manually. You have to F2/Enter the cells containing the functions
(or, in VBA, re-enter the formulae)

Puzzling, isn't it?

Pete



:

I saw that in your other post.

I think I would have just recalculated in the subroutine that hid/unhid the
rows.

Dave,

I modified my hide/unhide formulae to re-enter the custom functions into
their appropriate cells and it works OK. Can't wait for my Office XP upgrade!


Thanks

Pete

:


You could add:

application.volatile

At the top of your sub, but that just means that the function will calculate the
next time excel calculates. (and I'd remove the calculate from your UDF--I bet
it doesn't help!)

But hiding a row doesn't force calculation (until you get to xl2003). Maybe you
can add an "application.calculate" to the routine that hides the rows???

(In xl2003, =subtotal() has been enhanced to be able to ignore manually hidden
rows: =subtotal(109,a1:a22)

(100 + # means to ignore the manually hidden row.)

Peter Rooney wrote:

Hmm. Perhaps I should have been a little more specific with the problem.

I have a range of cells containing the numbers 1-10, with 4 buttons that run
macros to hide/unhide the rows containg the odd or even numbers.

It's when I run these macros to hide 1/3/5/7/8 (displaying 2/4/6/8/10) or
hide 2/4/6/8/10 (displaying 1/3/5/7/9) that the function doesn't recalculate.

There is a SumVisibleRows function too that does the opposite of
SumHiddenRows, displaying a total for all the visible cells in the range thus:

Function SumVisibleRows(TheVisibleRange)
Dim VisibleTotal As Long
Dim VisibleCell As Range

VisibleTotal = 0
For Each VisibleCell In TheVisibleRange
If VisibleCell.EntireRow.Hidden = False Then
VisibleTotal = VisibleTotal + VisibleCell.Value
End If
Next
SumVisibleRows = VisibleTotal
Calculate
End Function

If I change the value of a visible cell in the list, SumVisibleCells
correctly calculates the new value without F2, but neither formula calculates
new totals on its own when the hide/unhide macros are run.

Should this be some sort of Worksheet_Change macro instead, and if so, can
anyone advise on the syntax for picking up changes to the hidden property of
a row?

Thanks again

Pete

:


Good morning all!

I wrote a simple function to calculate the values of all hidden cells in a
range.
It works fine, except that I have to edit the formula with [F2] and [Enter]
before it displays the correct answer - otherwise, it just displays the
result of the previous calculation.

Can anyone help, please?

Thanks in advance

Pete

Function SumHiddenRows(TheHiddenRange)
Dim HiddenTotal As Long
Dim HiddenCell As Range

HiddenTotal = 0
For Each HiddenCell In TheHiddenRange
If HiddenCell.EntireRow.Hidden = True Then
HiddenTotal = HiddenTotal + HiddenCell.Value
End If
Next
SumHiddenRows = HiddenTotal
Calculate
End Function

 

[Dave Peterson]

I only run xl2003, so I can't test in xl2k or below.

But I don't recall any problems with using application.calculate in a sub (not a
function called from a worksheet cell).

(But that doesn't help you.)

Dave,

I did and it doesn't work - whether you put the calculate command in the
function or the hide/unhide macros. It doesn't even work if you press F9 to
recalculate manually. You have to F2/Enter the cells containing the functions
(or, in VBA, re-enter the formulae)

Puzzling, isn't it?

Pete

I saw that in your other post.

I think I would have just recalculated in the subroutine that hid/unhid the
rows.

Dave,

I modified my hide/unhide formulae to re-enter the custom functions into
their appropriate cells and it works OK. Can't wait for my Office XP upgrade!


Thanks

Pete

:

You could add:

application.volatile

At the top of your sub, but that just means that the function will calculate the
next time excel calculates. (and I'd remove the calculate from your UDF--I bet
it doesn't help!)

But hiding a row doesn't force calculation (until you get to xl2003). Maybe you
can add an "application.calculate" to the routine that hides the rows???

(In xl2003, =subtotal() has been enhanced to be able to ignore manually hidden
rows: =subtotal(109,a1:a22)

(100 + # means to ignore the manually hidden row.)

Peter Rooney wrote:

Hmm. Perhaps I should have been a little more specific with the problem.

I have a range of cells containing the numbers 1-10, with 4 buttons that run
macros to hide/unhide the rows containg the odd or even numbers.

It's when I run these macros to hide 1/3/5/7/8 (displaying 2/4/6/8/10) or
hide 2/4/6/8/10 (displaying 1/3/5/7/9) that the function doesn't recalculate.

There is a SumVisibleRows function too that does the opposite of
SumHiddenRows, displaying a total for all the visible cells in the range thus:

Function SumVisibleRows(TheVisibleRange)
Dim VisibleTotal As Long
Dim VisibleCell As Range

VisibleTotal = 0
For Each VisibleCell In TheVisibleRange
If VisibleCell.EntireRow.Hidden = False Then
VisibleTotal = VisibleTotal + VisibleCell.Value
End If
Next
SumVisibleRows = VisibleTotal
Calculate
End Function

If I change the value of a visible cell in the list, SumVisibleCells
correctly calculates the new value without F2, but neither formula calculates
new totals on its own when the hide/unhide macros are run.

Should this be some sort of Worksheet_Change macro instead, and if so, can
anyone advise on the syntax for picking up changes to the hidden property of
a row?

Thanks again

Pete

:

Good morning all!

I wrote a simple function to calculate the values of all hidden cells in a
range.
It works fine, except that I have to edit the formula with [F2] and [Enter]
before it displays the correct answer - otherwise, it just displays the
result of the previous calculation.

Can anyone help, please?

Thanks in advance

Pete

Function SumHiddenRows(TheHiddenRange)
Dim HiddenTotal As Long
Dim HiddenCell As Range

HiddenTotal = 0
For Each HiddenCell In TheHiddenRange
If HiddenCell.EntireRow.Hidden = True Then
HiddenTotal = HiddenTotal + HiddenCell.Value
End If
Next
SumHiddenRows = HiddenTotal
Calculate
End Function

 

[okaizawa]

Hi,
i wrote some code below.
a formula in a conditional format seems to be called when a cell
is repainted.
my idea is that making a volatile formula like
=SumHiddenRows(A1:A10)+NOW()*0
and setting an UDF in a format condition in the hidden/unhidden cells
(like '=CatchPaint()' in A1:A10), the hidden cell calls the UDF,
the UDF starts timer, the timer procedure calculates formulas.
i am not sure that this would work perfectly.
(i am testing this in excel 2000)

'Module1
Private Declare Function SetTimer Lib "user32" _
(ByVal hWnd As Long, ByVal nIDEvent As Long, _
ByVal uElapse As Long, ByVal lpTimerFunc As Long) As Long
Private Declare Function KillTimer Lib "user32.dll" _
(ByVal hWnd As Long, ByVal uIDEvent As Long) As Long

Private TimerId As Long

Private Function TimerProc(ByVal hWnd As Long, ByVal uMsg As Long, _
ByVal idEvent As Long, ByVal dwTime As Long) As Long

On Error Resume Next
KillTimer 0, idEvent

ActiveSheet.Calculate
'ActiveSheet.Range("A1").Calculate
'Application.Calculate 'this interferes with entering formula in xl2k

TimerId = 0
End Function

Private Function CatchPaint()
If TimerId = 0 Then TimerId = SetTimer(0, 0, 0, AddressOf TimerProc)
End Function

 

[David Welch]

Hi,
i wrote some code below.
a formula in a conditional format seems to be called when a cell
is repainted.
my idea is that making a volatile formula like
=SumHiddenRows(A1:A10)+NOW()*0
and setting an UDF in a format condition in the hidden/unhidden cells
(like '=CatchPaint()' in A1:A10), the hidden cell calls the UDF,
the UDF starts timer, the timer procedure calculates formulas.
i am not sure that this would work perfectly.
(i am testing this in excel 2000)

'Module1
Private Declare Function SetTimer Lib "user32" _
(ByVal hWnd As Long, ByVal nIDEvent As Long, _
ByVal uElapse As Long, ByVal lpTimerFunc As Long) As Long
Private Declare Function KillTimer Lib "user32.dll" _
(ByVal hWnd As Long, ByVal uIDEvent As Long) As Long

Private TimerId As Long

Private Function TimerProc(ByVal hWnd As Long, ByVal uMsg As Long, _
ByVal idEvent As Long, ByVal dwTime As Long) As Long

On Error Resume Next
KillTimer 0, idEvent

ActiveSheet.Calculate
'ActiveSheet.Range("A1").Calculate
'Application.Calculate 'this interferes with entering formula in xl2k

TimerId = 0
End Function

Private Function CatchPaint()
If TimerId = 0 Then TimerId = SetTimer(0, 0, 0, AddressOf TimerProc)
End Function

This won't work i'm afraid, the calculate function won't calculate the
relevant cell because excel 2000 and lower doesn't refresh its
calculation tree on hide/unhide events.