Question

I am trying to build a simple Java application with SWT using the MVC pattern. I would like to be able to automatically update the view when something happens in the background so I am trying to use the Observer/Observable pattern, but it looks like my Observer is never notified when my Observable changes.

Here is the code:

Launcher.java (main class)

public class Launcher {

    public static void main(String[] args) {
        Application app = new Application();
        PenguinView v = new PenguinView(app);
        Controller api = new Controller(app, v);
    }

}

Application.java (The background application)

public class Application {
    private Penguin _myPenguin;

    public Application() {
        _myPenguin = new Penguin();
        new Thread(_myPenguin).start();
    }

    public Penguin getPenguin() {
        return _myPenguin;
    }
}

Penguin.java (The model, my Observable)

public class Penguin extends Observable implements Runnable {
    private String _color;
    private boolean _isHappy;
    private int _myRocks;

    public Penguin() {
        _color = "Black";
        _isHappy = true;
        _myRocks = 0;
    }

    public void paint(String color) {
        _color = color;
        System.out.println("My new color is " + _color);
        setChanged();
        notifyObservers();
    }

    public String getColor() {
        return _color;
    }

    public void upset() {
        _isHappy = false;
        setChanged();
        notifyObservers();
    }

    public void cheerUp() {
        _isHappy = true;
        setChanged();
        notifyObservers();
    }

    public boolean isHappy() {
        return _isHappy;
    }

    public void run() {
        // Penguin starts walking and find rocks!
        while(true) {
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            iFoundRock();
        }
    }

    private void iFoundRock() {
        _myRocks++;
        System.out.println("I now have " + _myRocks + " rocks");
        setChanged();
        notifyObservers();
    }

}

PenguinView.java (The SWT View, my observer)

public class PenguinView implements Observer {
    private Application _app;

    private Display _d;
    private Shell _s;

    private Label _penguinColor;
    private Label _penguinHumor;
    private Label _penguinRocks;
    private Button _upset;
    private Button _cheerUp;
    private Text _newColor;
    private Button _paint;


    public PenguinView(Application app) {
        _app = app;
        _d = new Display();
        _s = new Shell();

        RowLayout rl = new RowLayout();
        rl.marginWidth = 12;
        rl.marginHeight = 12;
        _s.setLayout(rl);

        new Label(_s, SWT.BORDER).setText("Penguin Color: ");
        _penguinColor = new Label(_s, SWT.BORDER);
        _penguinColor.setText(_app.getPenguin().getColor());

        new Label(_s, SWT.BORDER).setText(" Humor: ");
        _penguinHumor = new Label(_s, SWT.BORDER);
        String humor = _app.getPenguin().isHappy() ? "Happy" : "Sad";
        _penguinHumor.setText(humor);

        new Label(_s, SWT.BORDER).setText(" Rocks: ");
        _penguinRocks = new Label(_s, SWT.BORDER);
        _penguinRocks.setText(String.valueOf(_app.getPenguin().howManyRocks()));

        _upset = new Button(_s, SWT.PUSH);
        _upset.setText(":(");
        _upset.addListener(SWT.Selection, new Listener(){
            public void handleEvent(Event e) {
                _penguinHumor.setText("Sad");
            }
        });

        _cheerUp = new Button(_s, SWT.PUSH);
        _cheerUp.setText(":)");
        _cheerUp.addListener(SWT.Selection, new Listener(){
            public void handleEvent(Event e) {
                _penguinHumor.setText("Happy");
            }
        });

        _newColor = new Text(_s, SWT.BORDER);

        _paint = new Button(_s, SWT.PUSH);
        _paint.setText("Paint!");
        _paint.addListener(SWT.Selection, new Listener(){
            public void handleEvent(Event e) {
                //_penguinColor.setText(_newColor.getText());
                _app.getPenguin().paint(_newColor.getText());
            }
        });

        _s.pack();
        _s.open();
        while (!_d.isDisposed()) {
            if (!_d.readAndDispatch()) {
                _d.sleep();
            }
        }
    }

    public void update(Observable obs, Object obj) {
        System.out.println("I go here!");
        _penguinRocks.setText(String.valueOf(((Penguin)obs).howManyRocks()));
        if(obs.equals(_app.getPenguin())) {
            _penguinRocks.setText(String.valueOf(((Penguin)obs).howManyRocks()));
        }
    }

    public void update(Observable obs) {
        System.out.println("I go there!");
    }

Controller.java (The controller)

public class Controller {
    Application _app;
    PenguinView _v;

    public Controller(Application app, PenguinView v) {
        _app = app;
        _v = v;

        // Set observer
        _app.getPenguin().addObserver(_v);
    }

}

The output:

I now have 1 rocks
I now have 2 rocks
My new color is Blue
I now have 3 rocks
I now have 4 rocks

Do you have any idea of what I am doing wrong?

Thanks!

Answer 1

From what I can tell, the while loop in the PenguinView constructor is blocking your main thread, so the Controller never gets instantiated and the observer is never added.