constraint programming

[Pieter]

Hi,

How can I include contraints in VB.NET (Windows Forms, 2.0), using Objects
with Propertys?

I need several property's be recalculated when others change, but not in a
straightforward way: When A is changed, B has to change, but when B changes,
A has to change (or C or ...).
Untill now I added routines in the Set-Property that calculated the other
Property, but I'm loosing the overview, and I would have referred to have
all this rules centrally placed. Also, I'm kind of affraid of endless loops:
A changes B, B changes A, which changed B again etc etc...

Is there a way to do some kind of constraint programming in VB.NET? Or how
should I implement such a thing the best way?

I need constraints like this:
- When the Currency changes, the AmountNewCurrency must be automaticly
changed to AmountOldCurrency * CurrencyRate
but:
When the user changes the in the TextBox the AmountNewCurrency, the
AmountOldCurrency must be changed too (AmountNewCurrency / CurrencyRate).

- Another one: TotalBuyPrice = the total Price we pay for all the Articles
TotalSellPrice = The total Price at which we sell the Articles
Percentage: the percentage we add to the TotalBuyPrice to have a sudden
TotalSellPrice.
-Is Percentage is changed, TotalSellPrice must be changed (and the
ArticleSellPrice accordingly).
but:
-When the TotalSellPrice is changed, the percentage has to be
calculated automaticly, and the ArticleSellPrice of each article has to be
changed proportionally

- and many many more...
Any help would be really appreciated,

Thansk a lot in advance,

Pieter

[Phill W.]

Pieter wrote:

I need several property's be recalculated when others change, but not in a
straightforward way: When A is changed, B has to change, but when B changes,
A has to change (or C or ...).

I usually use a flag to prevent recursive calls, something like

Class X
Private _bRecursionBuster As Boolean = False

Property A() As ?
Set(Value as ?)

If Not _bRecursionBuster Then
_bRecursionBuster = True

B = Value /2

_bRecursionBuster = False
End If

End Set
End Property

Property B() As ?
Set(Value as ?)

If Not _bRecursionBuster Then
_bRecursionBuster = True

A = Value * 2

_bRecursionBuster = False
End If

End Set
End Property

End Class

With multiple properties, you make update everything from each property
and, with a bit of luck, you don;t get all that nasty endless looping.

HTH,
Phill W.

[Branco Medeiros]

Pieter wrote:
<snip>

I need several property's be recalculated when others change, but not in a
straightforward way: When A is changed, B has to change, but when B changes,
A has to change (or C or ...).
Untill now I added routines in the Set-Property that calculated the other
Property, but I'm loosing the overview, and I would have referred to have
all this rules centrally placed. Also, I'm kind of affraid of endless loops:
A changes B, B changes A, which changed B again etc etc...

I'd use events to keep each class independent of each other.

Besides, if the changing of a value in some class might create an
endless loop then it seems you must put some safeguards in the code:

<aircode>
Class A
Public Event CurrencyChanged( _
Sender As Object, _
NewCurrency As Double)

Private mCurrency As Double

Property Currency As Double
Get
Return mCurrency
End Get

Set(Value As Double)
Static Busy As Boolean

If Value <mCurrency Then

If Busy Then
Throw New InvalidOperationException( _
"Set-Currency loop!" _
)
End If

Busy = True
mCurrency = Value
Try
RaiseEvent CurrencyChanged(Me, Value)
Finally
Busy = False
End Try
End If

End Set
End Property
End Class
</aircode>
HTH.

Regards,

Branco

[Nick Malik [Microsoft]]

I agree with Phil... update everything from each input to the function.

IOW, have a 'recalculate_page' method that calculates every function, from
currency to total price. Then, when the user changes any of the inputs,
from locale to quantity, whatever, call 'recalculate_page'.

--
--- Nick Malik [Microsoft]
MCSD, CFPS, Certified Scrummaster
http://blogs.msdn.com/nickmalik

Disclaimer: Opinions expressed in this forum are my own, and not
representative of my employer.
I do not answer questions on behalf of my employer. I'm just a
programmer helping programmers.
--
"Pieter" <pi****************@hotmail.comwrote in message
news:O1**************@TK2MSFTNGP06.phx.gbl...

Hi,

How can I include contraints in VB.NET (Windows Forms, 2.0), using Objects
with Propertys?

I need several property's be recalculated when others change, but not in a
straightforward way: When A is changed, B has to change, but when B
changes, A has to change (or C or ...).
Untill now I added routines in the Set-Property that calculated the other
Property, but I'm loosing the overview, and I would have referred to have
all this rules centrally placed. Also, I'm kind of affraid of endless
loops: A changes B, B changes A, which changed B again etc etc...

Is there a way to do some kind of constraint programming in VB.NET? Or how
should I implement such a thing the best way?

I need constraints like this:
- When the Currency changes, the AmountNewCurrency must be automaticly
changed to AmountOldCurrency * CurrencyRate
but:
When the user changes the in the TextBox the AmountNewCurrency, the
AmountOldCurrency must be changed too (AmountNewCurrency / CurrencyRate).

- Another one: TotalBuyPrice = the total Price we pay for all the Articles
TotalSellPrice = The total Price at which we sell the Articles
Percentage: the percentage we add to the TotalBuyPrice to have a sudden
TotalSellPrice.
-Is Percentage is changed, TotalSellPrice must be changed (and the
ArticleSellPrice accordingly).
but:
-When the TotalSellPrice is changed, the percentage has to be
calculated automaticly, and the ArticleSellPrice of each article has to be
changed proportionally

- and many many more...
Any help would be really appreciated,

Thansk a lot in advance,

Pieter