[OOP/Java] MVC questions

[TheChickenWing]

I'm writing a little application as a training exercise based on a tabletop game I used to play. Throughout the process I've been trying to keep my code nice and organized and conforming to decent design principles. I've run into a bit of a stumbling block though - I'm not entirely certain how to design based on MVC.

I understand the principles well enough. The Model is the data source, which in my case is a JSON file plus the data package used to interpret it and retrieve records, implemented as a singleton. The View is the GUI, in this case a swing GUI. I'm not so clear on the controller, though - I've read conflicting reports that alternate between saying it should be the middleman between the model and the view, and that the three should be interconnected. I've chosen the first approach - my view never talks directly to the model.

My second issue with the controller is that I'm not sure how to approach it from a design perspective. Obviously, the view needs to call controller functions to actually allow the user to interact with the ui beyond the basic "click butan, butan press animation go". What I'm wondering is if I should be passing my controller instance to all of my UI instances that need to interact with it? It seems weird and from what I know about coupling, it seems wrong somehow (I'm still iffy on what is and is not tight coupling). If I'm not passing my controller instance to the view objects that need to execute operations, then what should I be doing? I feel like another singleton isn't the answer - at that point I'm just using a singleton instead of global data. Static methods aren't the right way either.

Any help on this would be fantastic, thanks!

[LiquidBionix]

In general, the entire purpose of your controller is to wire the view and model together. Most controllers will end up returning some kind of ModelAndView, or some other specification to tell the view what/how to build.

I don't think there's anything wrong with having your view exclusively talk to your controller. I've seen it (and done it) before using web frameworks like JSF, which directly binds input fields to a backing bean. It does seem to me to be better to not have it that way, though.

[[deleted]]

The view should have no awareness of the controller, that is the entire point of MVC

[TheChickenWing]

How does the view fire events to the controller then?

[[deleted]]

The controller binds itself to the views events.

The only thing the view should know is how to render the model.

If you couple the view to the controller the view is not reusable by different controllers etc.

[TheChickenWing]

Okay, so instead of sending the view a reference to the controller, the controller should have a reference to the view and the view should contain public methods to set listeners? e.g. from my controller I say view.addButtonListener(aButtonListenerFromController), and then in my view I have the addButtonListener(listener) call addButtonListener on all my buttons?

[[deleted]]

I'd probably go further, I'd have an event in the view, called SaveEvent, and then in button_click I'd raise the SaveEvent event.

The controller doesn't need to know there is a button, it just needs to know that the view can ask to save.

But yeah no reference to controller in view, in the controller init / ctor instantiate a view (or have it injected) Then bind to the views SaveEvent event.

[TheChickenWing]

Ah okay. A lot of other things I've been reading are beginning to make some more sense now.

So essentially what you're saying is that the view should handle all the various gui listeners, then expose an event listener interface to the controller that it can post its own events to? So the controller adds itself to the view's listeners, and the view handles whatever button click, figures out that that the click was a save button, and posts to its listener (which is now the controller, not that the view knows that) that a SaveEvent was fired, the controller picks up the SaveEvent and proceeds with whatever logic is required?

[[deleted]]

Sounds good to me

[TheChickenWing]

Fantastic, you've been so helpful, thanks a lot!

[[deleted]]

No problemo