JavaFX EventHandler - new Alert if boolean equals true

Question

When the user has reached the end of this Tetris game I want a new alert to be opened.

In the model class I have a boolean that will switch to true if a new Tetris block cannot be spawned.

I'm working with model view presenter, so in the model is the boolean + getter and in the presenter a new alert will be created if the boolean returns true.

The question is how do I add this to the eventHandlers() in the presenter?

public Presenter(Model model, View view) {
this.model = model;
this.view = view;
addEventHandlers();
}

private void addEventHandlers() {
//view.setOnKeyPressed... this is for rotating the blocks to give you an example
}

You may want to use an observer design pattern: https://en.wikipedia.org/wiki/Observer_pattern — Krzysztof Kaszkowiak, Mar 14 '17 at 12:44
@KrzysztofKaszkowiak Thank you for that link, indeed it seems that I will need an observer to solve this. — m4t5k4, Mar 14 '17 at 13:09
@KrzysztofKaszkowiak JavaFX already [implements that for you](http://www.oracle.com/pls/topic/lookup?ctx=javase80&id=JFXBD107) — James_D, Mar 14 '17 at 15:15

score 1 · Accepted Answer · answered Mar 14 '17 at 15:22

JavaFX implements observable properties, which are extensions of the Java Bean pattern that support notification for invalidation and for changes to the underlying value. These are fundamental to the JavaFX library: all controls in JavaFX make use of these. So, for example, if you want to respond to changes to the text in a text field, you would do

myTextField.textProperty().addListener((observable, oldText, newText) -> {
    // ... do something with newText (and perhaps oldText) here...
});

So you can just achieve this with a BooleanProperty (or similar) in your model class:

private final BooleanProperty gameEnded = new SimpleBooleanProperty();

public BooleanProperty gameEndedProperty() {
    return gameEnded ;
}

public final boolean isGameEnded() {
    return gameEndedProperty().get();
}

public final void setGameEnded(boolean gameEnded) {
    gameEndedProperty().set(gameEnded);
}

Then you can do:

model.gameEndedProperty().addListener((obs, gameWasEnded, gameIsNowEnded) -> {
    if (gameIsNowEnded) {
        // show alert, etc...
    }
});

See "Properties and Bindings" in the Oracle tutorial for more details, including bindings, etc. You might also consider a ReadOnlyBooleanWrapper if you don't want the property to be changed from outside the class it is defined in.

Thank you, works like a charm and it's less writing. I have no idea how lambda's work so I just wrote an anonymous inner class. — m4t5k4, Mar 14 '17 at 16:11

score 0 · Answer 2 · answered Mar 14 '17 at 15:11

public void setEind() {
    boolean oldValue = this.eind;
    eind = true;
    System.out.println(eind);
    firePropertyChange("eind",oldValue,eind);

}

private final List<PropertyChangeListener> listeners = new ArrayList<>();

public void addPropertyChangeListener(PropertyChangeListener listener) {
    listeners.add(listener);
}
public void firePropertyChange(String property, Object oldValue, Object newValue) {
    for (PropertyChangeListener listener : listeners) {
        listener.propertyChange(new PropertyChangeEvent(this,property,oldValue,newValue));
    }
}

spel.addPropertyChangeListener(new PropertyChangeListener() {
        @Override
        public void propertyChange(PropertyChangeEvent evt) {
            val.stop();
            Alert alert = new Alert(Alert.AlertType.INFORMATION);
            alert.setHeaderText("Game over!");
            alert.setContentText("Enter your name in the next window for the highscores.");
            alert.setTitle("End");
            alert.show();
        }
    });

Why not just use a [`BooleanProperty`](http://docs.oracle.com/javase/8/javafx/api/javafx/beans/property/BooleanProperty.html) instead of reinventing the wheel like this? — James_D, Mar 14 '17 at 15:14
Oops, no idea I was reinventing it. After some reading I went with the third answer on this outdated question http://stackoverflow.com/questions/9969375/ — m4t5k4, Mar 14 '17 at 15:42

JavaFX EventHandler - new Alert if boolean equals true

2 Answers2