properties - Java 8: Observable List - Invalidation Listener nor Change Listener is called in case of property change

Question

I build a custom property and add it to a observable list. But no listener is called if property content is changed. The following code snippets shows you the 'building':

public static final class TestObject {
    private final ReadOnlyStringWrapper title = new ReadOnlyStringWrapper();
    private final BooleanProperty selected = new SimpleBooleanProperty(false);

    public TestObject(String title) {
        this.title.set(title);
    }

    public String getTitle() {
        return title.get();
    }

    public ReadOnlyStringProperty titleProperty() {
        return title.getReadOnlyProperty();
    }

    public boolean getSelected() {
        return selected.get();
    }

    public BooleanProperty selectedProperty() {
        return selected;
    }

    public void setSelected(boolean selected) {
        this.selected.set(selected);
    }

    @Override
    public int hashCode() {
        return Objects.hash(title.get());
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null || getClass() != obj.getClass()) {
            return false;
        }
        final TestObject other = (TestObject) obj;
        return Objects.equals(this.title.get(), other.title.get());
    }

    @Override
    public String toString() {
        return "TestObject{" +
                "title=" + title.get() +
                ", selected=" + selected.get() +
                '}';
    }
}

This is my POJO class with my internal property values like name and selected.

public static final class TestProperty extends SimpleObjectProperty<TestObject> {
    public TestProperty(String name) {
        super(new TestObject(name));
        init();
    }

    public TestProperty(TestObject testObject) {
        super(testObject);
        init();
    }

    public String getTitle() {
        return getValue().getTitle();
    }

    public void setSelected(boolean selected) {
        getValue().setSelected(selected);
    }

    public boolean getSelected() {
        return getValue().getSelected();
    }

    public BooleanProperty selectedProperty() {
        return getValue().selectedProperty();
    }

    public ReadOnlyStringProperty titleProperty() {
        return getValue().titleProperty();
    }

    @Override
    public void set(TestObject testObject) {
        super.set(testObject);
        init();
    }

    @Override
    public void setValue(TestObject testObject) {
        super.setValue(testObject);
        init();
    }

    private void init() {
        if (get() == null)
            return;

        get().titleProperty().addListener((v, o, n) -> fireValueChangedEvent());
        get().selectedProperty().addListener((v, o, n) -> {
            fireValueChangedEvent();
        });
    }
}

This is my custom property based on the POJO. All property changes will fire a change event for my custom property.

@Test
public void testSimple() {
    final AtomicInteger counter = new AtomicInteger(0);
    final TestProperty testProperty = new TestProperty("Test");
    testProperty.addListener(observable -> {
        System.out.println("New state: " + testProperty.get().toString());
        counter.incrementAndGet();
    });

    testProperty.setSelected(true);
    testProperty.setSelected(false);

    Assert.assertEquals(2, counter.intValue());
}

In this test you can see that the property change event works fine.

@Test
public void testList() {
    final AtomicInteger counter = new AtomicInteger(0);
    final ObservableList<TestProperty> observableList = new ObservableListWrapper<>(new ArrayList<>());
    observableList.add(new TestProperty("Test 1"));
    observableList.add(new TestProperty("Test 2"));
    observableList.add(new TestProperty("Test 3"));

    observableList.addListener(new ListChangeListener<TestProperty>() {
        @Override
        public void onChanged(Change<? extends TestProperty> change) {
            System.out.println("**************");
        }
    });
    observableList.addListener((Observable observable) -> {
        System.out.println("New state: " + ((TestProperty) observable).get().toString());
        counter.incrementAndGet();
    });

    observableList.get(1).setSelected(true);
    observableList.get(2).setSelected(true);
    observableList.get(1).setSelected(false);
    observableList.get(2).setSelected(false);

    Assert.assertEquals(4, counter.intValue());
}

But in this code you see that the observable list not called the invalidation listener nor the change listener if a property value has changed in list.

What is wrong?

Thanks.

Answer 1

To create an observable list that will send "list updated" notifications if properties of elements of the list change, you need to create the list with an extractor. The extractor is a Callback that maps each element of the list to an array of Observables. If any of the Observables changes, InvalidationListeners and ListChangeListeners registered with the list will be notified.

So in your testList() method, you can do

final ObservableList<TestProperty> observableList = FXCollections.observableList(
    new ArrayList<>(),
    (TestProperty tp) -> new Observable[]{tp.selectedProperty()});

If the title were able to change, and you also wanted the list to receive notifications when that happened, you could do that too:

final ObservableList<TestProperty> observableList = FXCollections.observableList(
    new ArrayList<>(),
    (TestProperty tp) -> new Observable[]{tp.selectedProperty(), tp.titleProperty()});

Note that because the extractor is a Callback (essentially a function), the implementation can be arbitrarily complex (observe one property conditionally based on the value of another, etc).