What is a nice way to bind buttons to model-methods through a controller in Java using Swing and MVC-pattern

Question

I have tried to adhere to the mvc pattern in the java code that I have written. I want to keep the view and model independant of the controller and from each other. I am also trying my best to use interfaces to keep things modular.

My view has JButtons that I want to "bind" to specific methods in the model through the controller. I have tried two approaches to still keep the view independent of controller:

1. Registered the controller as an ActionListener to the view-object. Pros: The void addListener(ActionListener listener) abstract method encapsulates this behaviour in the view interface, so more buttons can be added without changing the interface. It also decouples the controller from the view, since it does not know anything about the actual buttons in the view. It is also easier to add more views or more controllers, so it follows the open-closed principle well. Con: For the controller to know the nature of the ActionEvent, I have only been able to come up with using the ActionEvent.getActionCommaned() in a switch statement, so mapping each case to its' corresponding method in the model. This seem unsafe and prone to cause irritation, since it seems like bad practice to match strings like this.
2. I also came up with adding public addActionListener(ActionListener) methods for each button in the view, like addGasButtonListener(ActionListener). Then doing something like view.addGasListener(e -> model.gasVehicles(view.getGasAmount())) in the controller. Pro: This seems like it reduces the uncertainty of matching strings. Cons: It means I have to add these new methods to the view interface, and each time a new button is added I have to do the same, making it difficult to add new views that does not have anything to do with some of the methods.

Main question:

I prefer the first method since it seems better to me, but I still would like to find a way to avoid matching strings, and find some nice way to do it (more similar to the rigidity of the second way of binding buttons to methdods). Is there?

Follow-up (less important) question:

I should also mention that my controller contains an inner class TimerListener implements ActionListener, that contains the loop of the app that acts on ActionEvents from the Timer. It also acts on ActionEvents from buttons if approach number one is used, which is why my follow-up question is: how would I seperate this main loop that only cares about the timer, from the switch statement used to act on button events. Since the ActionEvent.getActionCommand() is null almost all the time, it would be nice to seperate the two. Is there a approach that would let me do that?

Answer 1

I don't really see the value of working with ActionListener instances in the first place.

From your own example:

view.addGasListener(e -> model.gasVehicles(view.getGasAmount()))

• You don't do anything with the actual event
• In case you decide to use a different UI element in the future that doesn't fire ActionEvents, you will have to change the type of the listener.

I would rather expose a custom listener/callback that the controller (or model) can register on the view:

void onGasAmountChange(double gasAmount);

That being said, you might be focusing too hard on having a model, view and controller. If you look at more complicated Swing components (JList, JTable, ...), they have a view component and a model (ListModel and TableModel).

You could do something similar and create your own model for your view, and let the view call the necessary methods on the model directly (just like it happens for those Swing components). That avoids having to write a bunch of one-liner listeners that basically delegate to the model.