constraint programming

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  • Pieter
    #1

    constraint programming

    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 AmountNewCurren cy must be automaticly
    changed to AmountOldCurren cy * CurrencyRate
    but:
    When the user changes the in the TextBox the AmountNewCurren cy, the
    AmountOldCurren cy must be changed too (AmountNewCurre ncy / 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
    ArticleSellPric e accordingly).
    but:
    -When the TotalSellPrice is changed, the percentage has to be
    calculated automaticly, and the ArticleSellPric e of each article has to be
    changed proportionally

    - and many many more...


    Any help would be really appreciated,

    Thansk a lot in advance,

    Pieter


    Tags: None
    • Phill W.
      #2
      Re: constraint programming

      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 _bRecursionBust er As Boolean = False

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

      If Not _bRecursionBust er Then
      _bRecursionBust er = True

      B = Value /2

      _bRecursionBust er = False
      End If

      End Set
      End Property

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

      If Not _bRecursionBust er Then
      _bRecursionBust er = True

      A = Value * 2

      _bRecursionBust er = 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.

        Comment

        • Nick Malik [Microsoft]
          #3
          Re: constraint programming

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

          IOW, have a 'recalculate_pa ge' 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_pa ge'.

          --
          --- 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" <pieterNOSPAMco ucke@hotmail.co mwrote in message
          news:O12ZPlHQHH A.4424@TK2MSFTN GP06.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 AmountNewCurren cy must be automaticly
          changed to AmountOldCurren cy * CurrencyRate
          but:
          When the user changes the in the TextBox the AmountNewCurren cy, the
          AmountOldCurren cy must be changed too (AmountNewCurre ncy / 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
          ArticleSellPric e accordingly).
          but:
          -When the TotalSellPrice is changed, the percentage has to be
          calculated automaticly, and the ArticleSellPric e of each article has to be
          changed proportionally
          >
          - and many many more...
          >
          >
          Any help would be really appreciated,
          >
          Thansk a lot in advance,
          >
          Pieter
          >

            Comment

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