MVC - circular dependency

Question

I need the view to hold a reference to the contoller because it needs to register the controller as an event listener. I need the contoller to hold a reference to the view, because upon button click, I need to be able to get the selected files in a list. (I have a list of files, and a button 'Add cluster', so when the button is clicked I need to get the selected files)

So in short I have:

Controller controller(view);
View view(controller);

I'm sure there's some bad design here, I just can't figure out how to avoid it..

Answer 1

I'm not sure what Java Technologies you're using, but in GWT applications -and using MVP pattern- there's no need of the View to have a reference to the Controller: All the communication between the Controller (or Presenter) and the View is made through an interface implemented by the View. In your particular case, your code should look like this:

Define a Display inteface:

public interface Display {
    public void registerEventListener(Listener aListener)
    public List getSelectedFiles ()
}

Let the View implement that interface:

public class View implements Display{
//The method implementations
}

And make all the necessary bindings in the controller:

public class Controller{
    private Display view;
    public Controller(){
        //Or use some DI technology
        this.view = new View();
        //Get a Listener implementation, maybe an Anonymous Inner Class
        this.view.registerEventListener(getListener());
    }

    public void processFiles(){
        List files = view.getSelectedFiles();
        //Do the processing here
    }

}

Answer 2

One possible solution:

• Simply give Controller an addView(View view) method
• Likewise for View give it an addController(Controller controller) method.
• Make it part of your documentation that these must be set before use.
• Make sure you check that the reference variables are not null before using them, since they won't be set in the constructor.