鼠标滚轮上的 JavaFX 事件已为 ScrollPane 完成

Question

我有一个 ScrollPane，上面有很多元素（与这个相同），最初我打算使用 setOnScrollFinished(this::scrollFinished); 事件，但是我现在通过研究发现这仅适用于触摸手势，并且尝试为 MouseWheel 找到折衷方案并不是很好，我只是找到了非常复杂的解决方案，这些解决方案并不能真正解决我需要的问题。

我最多就是给滚动条变化添加一个监听器：

vvalueProperty().addListener(new ChangeListener<Number>() {
            @Override
            public void changed(ObservableValue<? extends Number> observable, Number oldValue, Number newValue) {
                System.out.println("scroll time");
            }
        });

然而，这在滚动时不断触发，我正在寻找的是只会在我停止滚动后调用的东西。

我的最终目标是有一个系统，当我滚动时，它会运行一个事件，它将遍历我的每个元素，这样我就可以为它们分配一个图像，如果它们在 window 边界，如果不是，他们会删除图像。

这基本上是我的代码，取自之前帮助过我的好用户：

import javafx.application.Application;
import javafx.beans.property.DoubleProperty;
import javafx.beans.property.SimpleDoubleProperty;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.ScrollPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Priority;
import javafx.scene.layout.StackPane;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.IntStream;

public class ScrollPaneContentDemo extends Application {
    @Override
    public void start(Stage stage) throws Exception {
        List<Item> items = new ArrayList<>();
        IntStream.range(1, 1000).forEach(i -> items.add(new Item()));
        TestPanel root = new TestPanel(items);
        Scene scene = new Scene(root, 500, 500);
        stage.setScene(scene);
        stage.setTitle("ScrollPaneContent Demo");
        stage.show();
    }

    class TestPanel extends ScrollPane {
        private final int SPACING = 5;
        private final int ROW_MAX = 6;
        private DoubleProperty size = new SimpleDoubleProperty();

        public TestPanel(List<Item> items) {
            final VBox root = new VBox();
            root.setSpacing(SPACING);
            HBox row = null;
            int count = 0;
            for (Item item : items) {
                if (count == ROW_MAX || row == null) {
                    row = new HBox();
                    row.setSpacing(SPACING);
                    root.getChildren().add(row);
                    count = 0;
                }

                CustomBox box = new CustomBox(item);
                box.minWidthProperty().bind(size);
                row.getChildren().add(box);
                HBox.setHgrow(box, Priority.ALWAYS);
                count++;
            }
            setFitToWidth(true);
            setContent(root);

            double padding = 4;
            viewportBoundsProperty().addListener((obs, old, bounds) -> {
                size.setValue((bounds.getWidth() - padding - ((ROW_MAX - 1) * SPACING)) / ROW_MAX);
                });


        //setOnScroll(this::showImages);       //The problematic things

        vvalueProperty().addListener(new ChangeListener<Number>() {
        @Override
        public void changed(ObservableValue<? extends Number> observable, Number oldValue, Number newValue) {
            System.out.println("scroll test");           //The problematic things
        }
    });

        }
    }

    class CustomBox extends StackPane {
        private Item item;
        private Rectangle square;
               private int size = 20;

    public CustomBox(Item item) {
        setStyle("-fx-background-color:#99999950;");
        this.item = item;
        setPadding(new Insets(5, 5, 5, 5));
        square = new Rectangle(size, size, Color.RED);
        square.widthProperty().bind(widthProperty());
        square.heightProperty().bind(heightProperty());

        maxHeightProperty().bind(minWidthProperty());
        maxWidthProperty().bind(minWidthProperty());
        minHeightProperty().bind(minWidthProperty());
        getChildren().add(square);
    }
}

    class Item {
    }
}

Answer 1

您将必须侦听属性更改以检测滚动而不会丢失。不过，您不必在每次侦听器触发时都采取繁重的操作：只需记录它发生的时间，然后进行循环过滤并在需要时触发事件。这是：

随时注册滚动值更改（或 ScrollPane 调整大小）
设置一个循环，以较短的时间间隔（从用户角度）检查是否在超过 1 秒之前注册了更改。
发生这种情况时，让 ScrollPane 触发一个事件 - 我们称之为“滴答”- 和 un-register 最后滚动

对于循环，我们将使用一个 Timeline，其中 KeyFrame 将有一个 onFinished 处理程序大约每 100 毫秒在 JavaFX 应用程序线程上调用一次，以避免处理另一个线程。

class TickingScrollPane extends ScrollPane {

  //Our special event type, to be fired after a delay when scrolling stops
  public static final EventType<Event> SCROLL_TICK = new EventType<>(TickingScrollPane.class.getName() + ".SCROLL_TICK");

  // Strong refs to listener and timeline
  private final ChangeListener<? super Number> scrollListener; //Will register any scrolling
  private final Timeline notifyLoop;  //Will check every 100ms how long ago we last scrolled

  // Last registered scroll timing
  private long lastScroll = 0; // 0 means "no scroll registered"

  public TickingScrollPane() {
    super();

    /* Register any time a scrollbar moves (scrolling by any means or resizing)
     * /!\ will fire once when initially shown because of width/height listener */
    scrollListener = (_observable, _oldValue, _newValue) -> {
      lastScroll = System.currentTimeMillis();
    };
    this.vvalueProperty().addListener(scrollListener);
    this.hvalueProperty().addListener(scrollListener);
    this.widthProperty().addListener(scrollListener);
    this.heightProperty().addListener(scrollListener);
    //ScrollEvent.SCROLL works only for mouse wheel, but you could as well use it 

    /* Every 100ms, check if there's a registered scroll.
     * If so, and it's older than 1000ms, then fire and unregister it.
     * Will therefore fire at most once per second, about 1 second after scroll stopped */
    this.notifyLoop = new Timeline(new KeyFrame(Duration.millis(100), //100ms exec. interval
        e -> {
          if (lastScroll == 0)
            return;
          long now = System.currentTimeMillis();
          if (now - lastScroll > 1000) { //1000ms delay
            lastScroll = 0;
            fireEvent(new Event(this, this, SCROLL_TICK));
          }
        }));
    this.notifyLoop.setCycleCount(Timeline.INDEFINITE);
    this.notifyLoop.play();

  }

}

如果您的 ScrollPane 随时要从场景中移除，您可能需要添加一个方法来停止 TimeLine 以避免它继续运行并可能消耗内存。

完整的运行可用演示代码：

package application;

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.event.Event;
import javafx.event.EventType;
import javafx.geometry.BoundingBox;
import javafx.geometry.Bounds;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.ScrollPane;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;
import javafx.util.Duration;

class TickingScrollPane extends ScrollPane {

  //Our special event type, to be fired after a delay when scrolling stops
  public static final EventType<Event> SCROLL_TICK = new EventType<>(TickingScrollPane.class.getName() + ".SCROLL_TICK");

  // Strong refs to listener and timeline
  private final ChangeListener<? super Number> scrollListener; //Will register any scrolling
  private final Timeline notifyLoop;  //Will check every 100ms how long ago we last scrolled

  // Last registered scroll timing
  private long lastScroll = 0; // 0 means "no scroll registered"

  public TickingScrollPane() {
    super();

    /* Register any time a scrollbar moves (scrolling by any means or resizing)
     * /!\ will fire once when initially shown because of width/height listener */
    scrollListener = (_observable, _oldValue, _newValue) -> {
      lastScroll = System.currentTimeMillis();
    };
    this.vvalueProperty().addListener(scrollListener);
    this.hvalueProperty().addListener(scrollListener);
    this.widthProperty().addListener(scrollListener);
    this.heightProperty().addListener(scrollListener);
    //ScrollEvent.SCROLL works only for mouse wheel, but you could as well use it 

    /* Every 100ms, check if there's a registered scroll.
     * If so, and it's older than 1000ms, then fire and unregister it.
     * Will therefore fire at most once per second, about 1 second after scroll stopped */
    this.notifyLoop = new Timeline(new KeyFrame(Duration.millis(100), //100ms exec. interval
        e -> {
          if (lastScroll == 0)
            return;
          long now = System.currentTimeMillis();
          if (now - lastScroll > 1000) { //1000ms delay
            lastScroll = 0;
            fireEvent(new Event(this, this, SCROLL_TICK));
          }
        }));
    this.notifyLoop.setCycleCount(Timeline.INDEFINITE);
    this.notifyLoop.play();

  }

}

public class TickingScrollPaneTest extends Application {
  
  @Override
  public void start(Stage primaryStage) {
    
    try {
      
      //Draw our scrollpane, add a bunch of rectangles in a VBox to fill its contents
      TickingScrollPane root = new TickingScrollPane();
      root.setPadding(new Insets(5));
      VBox vb = new VBox(6);
      root.setContent(vb);
      final int rectsCount = 10;
      for (int i = 0; i < rectsCount; i++) {
        Rectangle r = new Rectangle(Math.random() * 900, 60); //Random width, 60px height
        r.setFill(Color.hsb(360. / rectsCount * i, 1, .85));   //Changing hue (rainbow style)
        vb.getChildren().add(r);
      }
      
      //Log every scroll tick to console
      root.addEventHandler(TickingScrollPane.SCROLL_TICK, e -> {
        System.out.println(String.format(
            "%s:\tScrolled 1s ago to (%s)",
            LocalDateTime.now().format(DateTimeFormatter.ISO_DATE_TIME),
            getViewableBounds(root)
            ));
      });
      
      //Show in a 400x400 window
      Scene scene = new Scene(root, 400, 400);
      primaryStage.setScene(scene);
      primaryStage.setTitle("TickingScrollPane test");
      primaryStage.show();
    } catch (Exception e) {
      e.printStackTrace();
    }
    
  }
  
  
  /**
   * Calculate viewable bounds for contents for ScrollPane
   * given viewport size and scroll position
   */
  private static Bounds getViewableBounds(ScrollPane scrollPane) {
    Bounds vbds = scrollPane.getViewportBounds();
    Bounds cbds = scrollPane.getContent().getLayoutBounds();
    double hoffset = 0;
    if (cbds.getWidth() > vbds.getWidth())
      hoffset = Math.max(0, cbds.getWidth() - vbds.getWidth()) * (scrollPane.getHvalue() - scrollPane.getHmin()) / (scrollPane.getHmax() - scrollPane.getHmin());
    double voffset = 0;
    if (cbds.getHeight() > vbds.getHeight())
      voffset = Math.max(0, cbds.getHeight() - vbds.getHeight()) * (scrollPane.getVvalue() - scrollPane.getVmin()) / (scrollPane.getVmax() - scrollPane.getVmin());
    Bounds viewBounds = new BoundingBox(hoffset, voffset, vbds.getWidth(), vbds.getHeight());
    return viewBounds;
  }

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

鼠标滚轮上的 JavaFX 事件已为 ScrollPane 完成

JavaFX event on Mouse Wheel Finished for ScrollPane

java

events

javafx

scroll

mouseevent