MVP on semi-complicated pages

Question

I'm working on .NET 3.5 form application with slightly complicated behaviour. It's for a book inventory. To give you an idea, a workflow would be:

• The user enters an ISBN code
• If the ISBN is valid, check whether it exists,
• If it's valid and it exists, show book details and enable save button, if not, show 'add book'-button,
• If it's not valid, show error,
• Eventually, the user will click 'save', so the entry will have to be saved.

That's four responsibilities:

• Validate ISBN,
• Check book existence,
• Show book details,
• Save new book details.

My question is: Should I keep the application logic in one MVP-structure or should I split it into four MVP-structures, one for each responsibility?

Keeping it in one MVP-structure would

• make the model more complicated
• make the tests setup more complicated (lots of setup code for each test to choose the right validator,returned book etc. even if they're not used),
• make the presentation logic easier to follow

Keeping it in separate MVP-structures would

• make the model simpler,
• create more but simpler tests for each presenter,
• put complexity in the interactions between the presenters (how would I signal a presenter that an ISBN is valid so that book details can be shown?)

I'm trying for the Presenter First-principles, so: - Keep the view dumb (so no events like "Presenter one validated the ISBN"), - Keep the presenters stateless, - Keep the models simple (enough)

Anyone has an idea on what's the best way to do this?

Answer 1

I would go with one Presenter but delegate the validation etc of ISBN numbers to a Service.

Something along these lines in the presenter to handle an ISBN being entered:

public void IsbnEntered()
{
    var isbn = view.Isbn;

    if (isbnService.NumberIsValid(isbn))
    {
        var details = isbnService.RetrieveDetailsForIsbn(isbn);

        if (details != null)
        {
            view.Display(details);
            view.EnableSaveButton();
        }
        else
        {
            view.DisplayError("ISBN could not be found");
        }
    }
    else
    {
        view.DisplayError("Invalid ISBN");
    }
}

Here the responsibilities are well defined. The IsbnService is responsible for ISBN handling, the View for display and input retrieval and the Presenter manages the interaction between the two.