JavaFX ListView 时间轴滚动动画跳跃（断断续续）

Question

我正在使用 JavaFX ListView 和 Timeline 来为列表的滚动设置动画。当滚动动画很慢时，文本会跳动（断断续续）。我尝试使用 AnimationTimer 滚动文本。在缓慢滚动期间，文本也很跳跃（断断续续）。 ListView 控件是虚拟视口特性所必需的。以下是使用 Java 版本 1.8 在我的 Mac 上重现问题的示例。

import javafx.animation.KeyFrame;
import javafx.animation.KeyValue;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Orientation;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ListView;
import javafx.scene.control.ScrollBar;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.HBox;
import javafx.scene.text.Text;
import javafx.stage.Stage;
import javafx.util.Duration;

import java.util.ArrayList;
import java.util.List;

public class Jumpy extends Application {

    ListView listView;
    Timeline timeline = new Timeline();
    double speed = 0.0000005;

    @Override
    public void start(Stage stage) throws Exception {
        List list = new ArrayList();
        for (int i = 0; i < 2000; i++) {
            Text text = new Text("Random line of text to show how it is choppy during scroll animation");
            text.setStyle("-fx-font-size: " + 4 + "em");
            list.add(text);
        }
        ObservableList observableList = FXCollections.observableList(list);
        listView = new ListView((observableList));
        listView.setPrefWidth(600);

        AnchorPane root = new AnchorPane();
        root.getChildren().addAll(listView, buttons());

        stage.setScene(new Scene(root));
        stage.show();
    }

    public void scroll() {
        ScrollBar scrollBar = getVerticalScrollBar();
        EventHandler scroll = new EventHandler<ActionEvent>() {
            public void handle(ActionEvent t) {
                scrollBar.setValue(scrollBar.getValue() + speed);
            }
        };

        timeline.setCycleCount(Timeline.INDEFINITE);
        timeline.setAutoReverse(false);
        KeyValue kv = new KeyValue(scrollBar.valueProperty(), 1);
        KeyFrame kf = new KeyFrame(Duration.seconds(0.017), scroll);
        timeline.getKeyFrames().add(kf);
        timeline.play();
    }

    public ScrollBar getVerticalScrollBar() {
        ScrollBar scrollBar = null;
        for (Node node : listView.lookupAll(".scroll-bar")) {
            if (node instanceof ScrollBar) {
                scrollBar = (ScrollBar) node;
                if ((scrollBar.getOrientation().compareTo(Orientation.VERTICAL)) == 0) {
                    break;
                }
            }
        }
        return scrollBar;
    }

    public HBox buttons() {
        HBox hBox = new HBox();
        Button start = new Button("start");
        start.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {
                scroll();
            }
        });
        Button slower = new Button("slower");
        slower.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {
                ScrollBar scrollBar = getVerticalScrollBar();
                EventHandler scroll = new EventHandler<ActionEvent>() {
                    public void handle(ActionEvent t) {
                        scrollBar.setValue(scrollBar.getValue() - 0.000001);
                    }
                };
                KeyFrame kf = new KeyFrame(Duration.millis(10.0D), scroll);
                timeline.getKeyFrames().add(kf);
            }

        });
        Button faster = new Button("faster");
        faster.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {
                ScrollBar scrollBar = getVerticalScrollBar();
                EventHandler scroll = new EventHandler<ActionEvent>() {
                    public void handle(ActionEvent t) {
                        scrollBar.setValue(scrollBar.getValue() + 0.000001);
                    }
                };
                KeyFrame kf = new KeyFrame(Duration.millis(10.0D), scroll);
                timeline.getKeyFrames().add(kf);

            }
        });
        hBox.getChildren().addAll(start, slower, faster);
        return hBox;
    }

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

Answer 1

如果您只是要使用 2000 个Node 实例来填充虚拟化控件，那么使用虚拟化控件是没有意义的：您一开始就完全破坏了使用虚拟化的所有好处。

用数据填充控件（例如，在本例中为Strings）并设置ListView 的样式或使用单元工厂来控制值的显示方式。

以下对我来说表现更好：

ListView<String> listView;
Timeline timeline = new Timeline();
double speed = 0.0000005;

@Override
public void start(Stage stage) throws Exception {
    List<String> list = new ArrayList<>();
    for (int i = 0; i < 2000; i++) {
        String text = "Random line of text to show how it is choppy during scroll animation";
        //  text.setStyle("-fx-font-size: " + 4 + "em");
        list.add(text);
    }
    ObservableList<String> observableList = FXCollections.observableList(list);
    listView = new ListView<String>((observableList));
    listView.setPrefWidth(600);

    listView.setStyle("-fx-font-size: 4em; ");

    AnchorPane root = new AnchorPane();
    root.getChildren().addAll(listView, buttons());

    stage.setScene(new Scene(root));
    stage.show();
}

在此更改之后，使用AnimationTimer 似乎仍然稍微顺畅一些。这是一个使用这种方法的示例（并删除了所有冗余代码）：

import java.util.ArrayList;
import java.util.List;

import javafx.animation.AnimationTimer;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.geometry.Orientation;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ListView;
import javafx.scene.control.ScrollBar;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;

public class Jumpy extends Application {

    ListView<String> listView;
    Timeline timeline = new Timeline();
    double increment = 2e-5 ;
    double speed = 5*increment ;

    AnimationTimer timer = new AnimationTimer() {

        private long lastUpdate = -1 ;
        private ScrollBar scrollbar ;

        @Override
        public void start() {
            scrollbar = getVerticalScrollBar();
            super.start();
        }

        @Override
        public void handle(long now) {
            if (lastUpdate < 0) {
                lastUpdate = now ;
                return ;
            }

            long elapsedNanos = now - lastUpdate ;
            double delta = speed * elapsedNanos / 1_000_000_000 ;
            scrollbar.setValue(scrollbar.getValue() + delta);

            lastUpdate = now ;
        }
    };

    @Override
    public void start(Stage stage) throws Exception {
        List<String> list = new ArrayList<>();
        for (int i = 0; i < 2000; i++) {
            String text = "Random line of text to show how it is choppy during scroll animation";
            list.add(text);
        }
        ObservableList<String> observableList = FXCollections.observableList(list);
        listView = new ListView<String>((observableList));
        listView.setPrefWidth(600);

        listView.setStyle("-fx-font-size: 4em; ");

        AnchorPane root = new AnchorPane();
        root.getChildren().addAll(listView, buttons());

        stage.setScene(new Scene(root));
        stage.show();
    }

    private ScrollBar getVerticalScrollBar() {
        ScrollBar scrollBar = null;
        for (Node node : listView.lookupAll(".scroll-bar")) {
            if (node instanceof ScrollBar) {
                scrollBar = (ScrollBar) node;
                if (scrollBar.getOrientation() == Orientation.VERTICAL) {
                    break;
                }
            }
        }
        return scrollBar;
    }

    private HBox buttons() {
        HBox hBox = new HBox();
        Button start = new Button("start");
        start.setOnAction(event -> timer.start());
        Button slower = new Button("slower");
        slower.setOnAction(event -> speed -= increment);
        Button faster = new Button("faster");
        faster.setOnAction(event -> speed += increment);
        hBox.getChildren().addAll(start, slower, faster);
        return hBox;
    }

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