Question

I have a data object with three fields, A, B and C. The problem is that the user can set any of them because:

A * B = C

So if a user starts off by setting A & B, C will be calculated. but then if a user set C, A gets recalculated, so there is an implicit anchoring that is happening based off the last field that the user set.

i want to avoid a solution with a lot of flag member variables. Any best practices on how i can code this class up without having a lot of stuff like this below

public class Object {      private double _A;      private double _B;      private double _C;       private bool _enteredA;      private bool _enteredB;      private bool _enteredC;  public double A { get     {      if (_enteredC)      {           return _C / _B;      }      else      {         return _A;      }   } } 

should the logic of setting A, B, and C always be on the ‘get’ or the ‘set’.

Is there any cleaner way to doing this?

Answer 1

So your rules are:

A = C / B B = C / A C = A * B 

What you’d need to do is remember the last two fields that the user entered, and from that, calculate the third. Therefore if they entered A and then B, then you calculate C. If they then change C, then recalculate A, and so on.

If you want to code it without using boolean flags, there’s a couple of different ways you could do that. A queue, or just a simple array/map would work:

editOrder = {A : 0, B : 0, C : 0 }  // (or just use 0, 1, 2) editCount = 0;  every time any field is edited :     editCount = editCount + 1     editOrder[field] = editCount     if two fields have an editOrder > 0         recalculate the field with the lowest editOrder 

Example usage:

Field changed    editOrder        recalculate field     A            1,0,0            -     A            2,0,0            -     B            2,3,0            C     C            2,3,4            A     C            2,3,5            A     B            2,6,5            A     A            7,6,5            C