JavaFX 滚动开始和结束

Question

我有一个非常昂贵的操作要在 Pane 上滚动鼠标。我目前使用

pane.setOnScroll({myMethod()}).

问题是，如果您滚动很多次，它会多次计算所有内容。所以我想要的是仅在滚动完成时执行我的操作。我希望使用 setOnScrollStarted，保存起始值并使用 setOnScrollFinished 来执行我的操作。

但我不知道为什么这两个方法从来没有被调用过。作为测试，我使用了

pane.setOnScroll({System.out.println("proof of action"});

而且它显然从未被调用过。

知道如何仅在滚动结束时调用我的方法吗？

提前致谢

Answer 1

来自javadoc of ScrollEvent (强调我的):

When the scrolling is produced by a touch gesture (such as dragging a finger over a touch screen), it is surrounded by the SCROLL_STARTED and SCROLL_FINISHED events. Changing number of involved touch points during the scrolling is considered a new gesture, so the pair of SCROLL_FINISHED and SCROLL_STARTED notifications is delivered each time the touchCount changes. When the scrolling is caused by a mouse wheel rotation, only a one-time SCROLL event is delivered, without the started/finished surroundings.

可能的解决方法:

每次检测到滚动时增加一个计数器变量。在监听器中启动一个等待 1 秒的新线程，仅当计数器等于 1(最后一次滚动)时才执行您想要的操作，然后递减计数器。

我创建了一个 Gist ，但我将代码复制到这里:

public class ScrollablePane extends Pane {
    private Integer scrollCounter = 0;

    private final ObjectProperty<EventHandler<? super ScrollEvent>> onScrollEnded = new SimpleObjectProperty<>();

    public final ObjectProperty<EventHandler<? super ScrollEvent>> onScrollEndedProperty() {
        return onScrollEnded;
    }

    public ScrollablePane() {
        this.setOnScroll(e -> {
            scrollCounter++;

            Thread th = new Thread(() -> {
                try {
                    Thread.sleep(1000);
                    if (scrollCounter == 1)
                        onScrollEnded.get().handle(e);

                    scrollCounter--;
                } catch (Exception e1) {
                    e1.printStackTrace();
                }
            });
            th.setDaemon(true);
            th.start();
        });
    }

    public void setOnScrollEnded(EventHandler<? super ScrollEvent> handler) {
        onScrollEnded.setValue(handler);
    }
}

使用方法:

public class MyApplication extends Application {


    @Override
    public void start(Stage primaryStage) {
        try {
            BorderPane root = new BorderPane();
            Scene scene = new Scene(root, 400, 400);

            ScrollablePane pane = new ScrollablePane();
            pane.setOnScrollEnded(e -> System.out.println("Scroll just has been ended"));

            root.setCenter(pane);
            primaryStage.setScene(scene);
            primaryStage.show();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

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