Invoking ViewModel related code from Model

Question

The thing is that sometimes a Model should notify a ViewModel to show a message box, for example. Sometimes a Model should change the state of a ViewModel. What are the proper ways of doing such notifications?

Are there any helpful patterns or something?

events are clumsy. How about the Observer? – EngineerSpock Feb 12 '15 at 09:22 — EngineerSpock, Feb 12 '15 at 09:22
Don't .Net events already implement that pattern? – Clemens Feb 12 '15 at 09:39 — Clemens, Feb 12 '15 at 09:39

score 1 · Accepted Answer · answered Feb 15 '15 at 15:51

There is no single right answer, it is a design decision.

The possible alternatives:

Model can expose event members.
Model can implement IObservable<T> interface or expose the IObservable<T> -members. By the way, there is the Observable.FromEventPattern Method which allows to convert a .NET event to an observable sequence.
Model can use callback interfaces. For example, just to demonstrate the idea:

interface INumberHandler
{
    void Handle(int number);
}

class NumberViewModel : INumberHandler
{
}

class NumberService
{
    public void Calculate(INumberHandler handler)
    {
        handler.Handle(9);
    }
}

Invoking ViewModel related code from Model

1 Answers1