JavaFX:如果ObservableList的元素发生更改,则更新ListView

Question

我想使用JavaFX ListView控件显示一个人员列表(用POJOS编码,并包含名称和姓氏属性).我创建了ListView并将人员列表添加为ObservableList.如果我删除或向ObservableList添加新人,一切正常,但POJO中的更改不会触发ListView的更新.我必须从ObservableList中删除并添加修改后的POJO以触发ListView的更新.如果没有上述解决方法,是否有可能在POJOS中显示更改？

Answer 1

您的问题有几个方面(我不完全是问题所在:-)我会假设您的POJO以某种方式通知侦听器有关更改,可能是通过成为一个完整的JavaBean,这符合其通知通过触发属性合同根据需要更改事件或其他一些方法 - 否则,您无论如何都需要手动推送更改.

使FX-ObservableList通知其自己的侦听器有关包含元素的突变的基本方法是使用提供Observable数组的自定义Callback来配置它.如果元素具有fx属性,您可以执行以下操作:

Callback<Person, Observable[]> extractor = new Callback<Person, Observable[]>() {

    @Override
    public Observable[] call(Person p) {
        return new Observable[] {p.lastNameProperty(), p.firstNameProperty()};
    }
};
ObservableList<Person> teamMembers = FXCollections.observableArrayList(extractor);
// fill list

如果pojo是一个完整的核心javaBean,它的属性必须通过使用JavaBeanProperty来适应fx-properties,fi:

Callback<PersonBean, Observable[]> extractor = new Callback<PersonBean, Observable[]>() {
    List<Property> properties = new ArrayList<Property>();
    @Override
    public Observable[] call(PersonBean arg0) {
        JavaBeanObjectProperty lastName = null;
        JavaBeanObjectProperty age = null;
        try {
            lastName = JavaBeanObjectPropertyBuilder.create()
                    .bean(arg0).name("lastName").build();
            age = JavaBeanObjectPropertyBuilder.create()
                    .bean(arg0).name("age").build();
            // hack around loosing weak references ... 
            properties.add(age);
            properties.add(lastName);
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }
        return new Observable[] {lastName, age};
    }

};
ObservableList<Person> teamMembers = FXCollections.observableArrayList(extractor);
// fill list

请注意一个警告:如果没有对某个地方适应的属性进行强有力的引用,它们将很快被垃圾收集 - 然后看起来根本没有任何影响(一次又一次陷入陷阱,不知道如果有一个好的策略如何躲开它).

对于任何其他(可能是粗粒度)通知的方法,您可以实现自定义适配器:下面的适配器侦听bean的所有propertyChanges,监听其他类型的事件将是非常类似的.

/**
 * Adapt a Pojo to an Observable.
 * Note: extending ObservableValue is too much, but there is no ObservableBase ...
 *
 * @author Jeanette Winzenburg, Berlin
 */
public class PojoAdapter<T> extends ObservableValueBase<T> {

    private T bean;
    private PropertyChangeListener pojoListener;
    public PojoAdapter(T pojo) {
        this.bean = pojo;
        installPojoListener(pojo);
    }

    /**
     * Reflectively install a propertyChangeListener for the pojo, if available.
     * Silently does nothing if it cant.
     * @param item
     */
    private void installPojoListener(T item) {
        try {
            Method method = item.getClass().getMethod("addPropertyChangeListener", 
                  PropertyChangeListener.class);
            method.invoke(item, getPojoListener());
        } catch (NoSuchMethodException | SecurityException | IllegalAccessException | 
                  IllegalArgumentException | InvocationTargetException e) {
            e.printStackTrace();
        }
    }
    /**
     * Returns the propertyChangeListener to install on each item.
     * Implemented to call notifyList.
     * 
     * @return
     */
    private PropertyChangeListener getPojoListener() {
        if (pojoListener == null) {
            pojoListener = new PropertyChangeListener() {

                @Override
                public void propertyChange(PropertyChangeEvent evt) {
                    fireValueChangedEvent();
                }
            };
        }
        return pojoListener;
    }

    @Override
    public T getValue() {
        return bean;
    }

}

它的用法与上面相同(变得无聊,不是它:-)

Callback<PersonBean, Observable[]> extractor = new Callback<PersonBean, Observable[]>() {

    @Override
    public Observable[] call(PersonBean arg0) {
        return new Observable[] {new PojoAdapter<PersonBean>(arg0)};
    }

};
ObservableList<Person> teamMembers = FXCollections.observableArrayList(extractor);
// fill list

不幸的是,由于仅在jdk8中修复的错误,具有如此酷列表的ListView的自动更新将无法可靠地工作.在早期版本中,您回到方块1 - 以某种方式监听更改,然后手动更新列表:

protected void notifyList(Object changedItem) {
    int index = list.indexOf(changedItem);
    if (index >= 0) {
        // hack around RT-28397
        //https://javafx-jira.kenai.com/browse/RT-28397
        list.set(index, null);
        // good enough since jdk7u40 and jdk8
        list.set(index, changedItem);
    }
}

Answer 2

使用弗朗西斯的想法我做了：

   list.set(list.indexOf(POJO), POJO);

可能不是最好的解决方案，但有效。

Answer 3

您可以通过调用从中继承的方法手动触发ListView.EditEvent- 这将导致ListView更新.例如,ListView::fireEventjavafx.scene.Node

/**
 * Informs the ListView that one of its items has been modified.
 *
 * @param listView The ListView to trigger.
 * @param newValue The new value of the list item that changed.
 * @param i The index of the list item that changed.
 */
public static <T> void triggerUpdate(ListView<T> listView, T newValue, int i) {
    EventType<? extends ListView.EditEvent<T>> type = ListView.editCommitEvent();
    Event event = new ListView.EditEvent<>(listView, type, newValue, i);
    listView.fireEvent(event);
}

或者作为一个班轮,

listView.fireEvent(new ListView.EditEvent<>(listView, ListView.editCommitEvent(), newValue, i));

这是一个演示其用途的示例应用程序.

/**
 * An example of triggering a JavaFX ListView when an item is modified.
 * 
 * Displays a list of strings.  It iterates through the strings adding
 * exclamation marks with 2 second pauses in between.  Each modification is
 * accompanied by firing an event to indicate to the ListView that the value
 * has been modified.
 * 
 * @author Mark Fashing
 */
public class ListViewTest extends Application {

    /**
     * Informs the ListView that one of its items has been modified.
     *
     * @param listView The ListView to trigger.
     * @param newValue The new value of the list item that changed.
     * @param i The index of the list item that changed.
     */    
    public static <T> void triggerUpdate(ListView<T> listView, T newValue, int i) {
        EventType<? extends ListView.EditEvent<T>> type = ListView.editCommitEvent();
        Event event = new ListView.EditEvent<>(listView, type, newValue, i);
        listView.fireEvent(event);
    }

    @Override
    public void start(Stage primaryStage) {
        // Create a list of mutable data.  StringBuffer works nicely.
        final List<StringBuffer> listData = Stream.of("Fee", "Fi", "Fo", "Fum")
                .map(StringBuffer::new)
                .collect(Collectors.toList());
        final ListView<StringBuffer> listView = new ListView<>();
        listView.getItems().addAll(listData);
        final StackPane root = new StackPane();
        root.getChildren().add(listView);
        primaryStage.setScene(new Scene(root));
        primaryStage.show();
        // Modify an item in the list every 2 seconds.
        new Thread(() -> {
            IntStream.range(0, listData.size()).forEach(i -> {
                try {
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(listData.get(i));
                Platform.runLater(() -> {
                    // Where the magic happens.
                    listData.get(i).append("!");
                    triggerUpdate(listView, listData.get(i), i);
                });            
            });
        }).start();
    }

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

}

Answer 4

ObservableList<String> items = FXCollections.observableArrayList();
ListView lv;
lv.setItems(items);
items.add();
items.remove;