Question

Say you have 5 or 6 variables in the model which a certain View is interested in, do you write different functions for each, such as

int a;
int b;
int c;

void setA( newA ) {
   a = newA;
   notifyAObservers();
}

void setB( newB ) {
   b = newB;
   notifyBObservers();
}

void setC( newC ) {
   b = newC;
   notifyCObservers();
}

Or do you just have one notify method and waste a little bit of CPU time

i.e. instead of notifyAObservers and notifyBObservers, you just have notifyObservers

Answer 1

I believe the traditional approach is to notify all observers, and let them handle it. This is because you don’t know which observers are observing which variable(s) – you just know that they want to be notified when something changes. However, if you do know what observers are observing which variables, and performance is critical, then you might be able to do something like what you have.

In the traditional Observer pattern, the Observers implement an update() method that is called by the controller when a change happens. The Observables (the data model) would have a notifyObservers() method that iterates over the Observers and calls their update() method. Then, the Observers get whatever they need and the view updates.

Any time I have implemented the Observer pattern, however, I simply keep a list of observers and notify them all. That way, I only have one list of observers and the rest of the class as well as the different observers can all change without me making any changes to the observable class notification.