JavaFX ObservableList（提取器更新事件在应该触发时未触发）

Question

一点背景：

public class Person {
    private final BooleanProperty adult;

    public Person(boolean adult) {
        this.adult = new SimpleBooleanProperty(adult);

        // Randomize "adult" value every 5 seconds
        ListViewExtractorTest.scheduledExecutorService.scheduleAtFixedRate(() -> {
            this.adult.set(Math.random() > 0.5);
            System.out.println("Updating adult: " + this);
        }, 5, 5, TimeUnit.SECONDS);

    // Getters setters
}

public class PersonUI {

    private final Person person;
    private final BooleanProperty adult;

    public PersonUI(Person person) {
        this.person = person;
        adult = new SimpleBooleanProperty(person.isAdult());
        person.adultProperty().addListener((observableValue, oldValue, newValue) -> {
            Platform.runLater(() -> this.adult.set(newValue));
        });
    }

    // Getters and setters
}

我对ObservableList也做了同样的操作--创建了一个将ListChangeListener添加到源列表的方法，并且每当更新源列表时，它将使用JavaFX线程上的UI等价类更新目标列表：

public static <T, R> ObservableList<R> bindListContentPlatformRunLater(ObservableList<T> srcList, Function<T, R> function, ObservableList<R> dstList) {
    for (T item : srcList) {
        dstList.add(function.apply(item));
    }
    // Maybe should wrap the whole while loop in Platform.runLater()
    // Less runnables, but big changes might hang up the UI.
    srcList.addListener((ListChangeListener<? super T>) change -> {
        while (change.next()) {
            int from = change.getFrom();
            int to = change.getTo();
            if (change.wasPermutated()) {
                Platform.runLater(() -> dstList.subList(from, to).clear());
                List<? extends T> addItems = change.getList().subList(from, to);
                for (int i = 0; i < addItems.size(); i++) {
                    final int index = i;
                    T addItem = addItems.get(i);
                    Platform.runLater(() -> dstList.add(from + index, function.apply(addItem)));
                }
            } else {
                if (change.wasRemoved()) {
                    int removedSize = change.getRemovedSize();
                    Platform.runLater(() -> dstList.subList(from, from + removedSize).clear());
                }

                if (change.wasAdded()) {
                    List<? extends T> addedSubList = change.getAddedSubList();
                    for (int i = 0; i < addedSubList.size(); i++) {
                        final int index = i;
                        T item = addedSubList.get(i);
                        Platform.runLater(() -> dstList.add(from + index, function.apply(item)));
                    }
                }
            }
        }
    });
    return dstList;
}

因此，现在如果我有更新的observableList 并且其项属性更新不是在JavaFX线程上，我就可以轻松地获得一个在JavaFX中显示的列表：

ObservableList<PersonUI> secondList = FXCollections.observableArrayList(personUI -> new Observable[]{personUI.adultProperty()});
UIClassUtil.bindListContentPlatformRunLater(originalList, PersonUI::new, secondList);

所以现在的问题是：

我的预期是，当secondList显示在ListView 中时，只要Person#AdultProperty值发生更改，它就会更新，但预期的行为只持续几秒钟，之后ListView停止更新，这是因为secondList“update”事件停止触发。我猜PersonUI#adultProperty会在几秒钟后被垃圾收集，因为它除了在提取器中外没有在其他地方使用？？

为了重现这个问题，我每隔几秒钟随机更改Person#adultProperty的值。不含Person和PersonUI类的完整代码：

public final class ListViewExtractorTest extends Application {

    private static final ObservableList<Person> originalList = FXCollections.observableArrayList();
    private static final ScheduledExecutorService scheduledExecutorService = Executors.newSingleThreadScheduledExecutor();

    static {
        for ( int a = 0; a < 5; a++ ) {
            originalList.add(new Person(Math.random() > 0.5));
        }
    }

    @Override
    public void start(Stage stage) throws Exception {
        ObservableList<PersonUI> secondList = FXCollections.observableArrayList(personUI -> new Observable[]{personUI.adultProperty()});
        UIClassUtil.bindListContentPlatformRunLater(originalList, PersonUI::new, secondList);

        secondList.addListener((ListChangeListener<? super PersonUI>) change -> {
            while (change.next()) {
                if (change.wasUpdated()) {
                    System.out.println("List updated!");
                }
            }
        });
        ListView<PersonUI> listViewPerson = new ListView<>(secondList);
        ListView<PersonUI> listViewForceRefresh = new ListView<>(secondList);
        stage.setScene(new Scene(new HBox(5, listViewPerson, listViewForceRefresh)));
        stage.setTitle("Hello");
        stage.show();

        scheduledExecutorService.scheduleAtFixedRate(() -> {
            Platform.runLater(listViewForceRefresh::refresh);
        }, 0, 100, TimeUnit.MILLISECONDS);
    }


    public static void main(String[] args) {
        launch();
    }
}

因此，我有两个ListView:左边的一个在Person#AdultProperty值更改时更新，右边的一个我强制每100ms刷新一次。起初，列表是同步的，但几秒钟后，只有右边的列表显示正确的值，左边的列表则停留在相同的值上，ListChangeListener的“list Updated”只在相同的头几秒钟内打印。这意味着列表的“Update”事件只在相同的最初几秒内被激发。

但是，一旦我开始使用PersonUI#adultProperty（每隔几秒钟使用另一个线程在控制台中打印一次），它就开始以预期的行为运行，所以我猜测如果不使用它，它就会被垃圾回收。

有任何想法，我如何使UI类的这些属性工作，只要UI类本身是活的，或者以某种方式实现预期的行为？

Answer 1

防止属性过早被垃圾收集的一个简单修复方法是从以下位置更新PersonUI构造函数中的侦听器：

person.adultProperty().addListener((observableValue, oldValue, newValue) -> {
    Platform.runLater(() -> this.adult.set(newValue));
});

致：

person.adultProperty().addListener((observableValue, oldValue, newValue) -> {
    this.adult.get()
    Platform.runLater(() -> this.adult.set(newValue));
});