Javafx StackedBarChart bug

Question

I'm developing an application using some StackedBarChart but i've found what i think is a little bug, negative values are not rendered if the animated property of the chart is set to false. Try the code below to test it, anyone know how to solve it ?

Thanks in advance.

import javafx.application.Application;
import javafx.application.Platform;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.chart.CategoryAxis;
import javafx.scene.chart.NumberAxis;
import javafx.scene.chart.StackedBarChart;
import javafx.scene.chart.XYChart;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
import javafx.stage.WindowEvent;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;

/**
 * Created by fabiofrumento on 28/04/15.
 */
public class Scratch extends Application {

    private static final SimpleDateFormat ONESECOND_CHART_DATE_FORMAT = new SimpleDateFormat("HH:mm:ss",
                                                                                             Locale.ENGLISH);
    private boolean stopThreads;

    CategoryAxis xAxisActive   = new CategoryAxis();
    CategoryAxis xAxisReactive = new CategoryAxis();
    NumberAxis   yAxisActive   = new NumberAxis();
    NumberAxis   yAxisReactive = new NumberAxis();

    {
        xAxisActive.setLabel("Time");
        xAxisReactive.setLabel("Time");
        yAxisActive.setLabel("animated = false");
        yAxisReactive.setLabel("animated = true");
    }

    private StackedBarChart<String, Number> onesecondActiveBarChart         = new StackedBarChart<String, Number>(xAxisActive,
                                                                                                                  yAxisActive);
    private StackedBarChart<String, Number> onesecondReactiveBarChart       = new StackedBarChart<String, Number>(xAxisReactive,
                                                                                                                  yAxisReactive);
    private XYChart.Series<String, Number>  onesecondActiveConsumedSerie    = new XYChart.Series<>();
    private XYChart.Series<String, Number>  onesecondActiveGeneratedSerie   = new XYChart.Series<>();
    private XYChart.Series<String, Number>  onesecondReactiveConsumedSerie  = new XYChart.Series<>();
    private XYChart.Series<String, Number>  onesecondReactiveGeneratedSerie = new XYChart.Series<>();

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

    @Override
    public void start(Stage primaryStage) throws
                                          Exception {
        VBox root = new VBox();

        initCharts();

        root.getChildren()
            .addAll(onesecondActiveBarChart,
                    onesecondReactiveBarChart);
        Scene scene = new Scene(root,
                                1024,
                                768);

        primaryStage.setTitle("JecomoduleUI");
        primaryStage.setScene(scene);
        primaryStage.setFullScreen(true);
        primaryStage.setOnCloseRequest(new EventHandler<WindowEvent>() {
            @Override
            public void handle(WindowEvent event) {
                stopThreads = true;
            }
        });

        primaryStage.show();
        new Thread(new Runnable() {
            @Override
            public void run() {
                while (!stopThreads) {
                    try {
                        Thread.sleep(1000);
                        Platform.runLater(new Runnable() {
                            @Override
                            public void run() {
                                updateActiveData();
                            }
                        });
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }).start();

    }

    private void initCharts() {
        onesecondActiveConsumedSerie.setName("Cons. W");
        onesecondActiveGeneratedSerie.setName("Gen. W");
        onesecondReactiveConsumedSerie.setName("Cons. VAR");
        onesecondReactiveGeneratedSerie.setName("Gen.. VAR");
        onesecondActiveBarChart.getData()
                               .addAll(onesecondActiveConsumedSerie,
                                       onesecondActiveGeneratedSerie);
        onesecondActiveBarChart.setAnimated(false);
        onesecondReactiveBarChart.getData()
                                 .addAll(onesecondReactiveConsumedSerie,
                                         onesecondReactiveGeneratedSerie);
    }

    void updateActiveData() {
        Date    format = new Date();
        Integer oneSecondActiveConsumedValue;
        Integer oneSecondActiveGeneratedValue;
        Double  rand   = Math.random();
        Integer rnd    = new Double(1000l + rand * 9000l).intValue();
        if (rnd % 2 == 0) {
            oneSecondActiveConsumedValue = rnd;
            oneSecondActiveGeneratedValue = 0;
        } else {
            oneSecondActiveConsumedValue = 0;
            oneSecondActiveGeneratedValue = 0 - rnd;
        }
        onesecondActiveConsumedSerie.getData()
                                    .add(new XYChart.Data<String, Number>(ONESECOND_CHART_DATE_FORMAT.format(format),
                                                                          oneSecondActiveConsumedValue));
        if (onesecondActiveConsumedSerie.getData()
                                        .size() > 10)
            onesecondActiveConsumedSerie.getData()
                                        .remove(0);
        onesecondActiveGeneratedSerie.getData()
                                     .add(new XYChart.Data<String, Number>(ONESECOND_CHART_DATE_FORMAT.format(format),
                                                                           oneSecondActiveGeneratedValue));
        if (onesecondActiveGeneratedSerie.getData()
                                         .size() > 10)
            onesecondActiveGeneratedSerie.getData()
                                         .remove(0);

        onesecondReactiveConsumedSerie.getData()
                                      .add(new XYChart.Data<String, Number>(ONESECOND_CHART_DATE_FORMAT.format(format),
                                                                            oneSecondActiveConsumedValue));
        if (onesecondReactiveConsumedSerie.getData()
                                          .size() > 10)
            onesecondReactiveConsumedSerie.getData()
                                          .remove(0);
        onesecondReactiveGeneratedSerie.getData()
                                       .add(new XYChart.Data<String, Number>(ONESECOND_CHART_DATE_FORMAT.format(format),
                                                                             oneSecondActiveGeneratedValue));
        if (onesecondReactiveGeneratedSerie.getData()
                                           .size() > 10)
            onesecondReactiveGeneratedSerie.getData()
                                           .remove(0);
    }

}

Answer 1

Yes, this seems to be a JavaFX error (Java 8u60).

Looking at the source code of StackedBarChart, an item with negative value gets drawn correctly only if "negative" is found in the style classes of the item's node (see StackedBarChart#layoutPlotChildren).

The "negative" style should be set by StackedBarChart#dataItemAdded. For animated charts StackedBarChart#animateData is called, where the "negative" style is added to the node if the item's value is negative.

For non-animated data, the node gets added to the chat's plot children without updating the style class.

---

As a workaround, override dataItemAdded of onesecondActiveBarChart:

private StackedBarChart<String, Number> onesecondActiveBarChart = new StackedBarChart<String, Number>(xAxisActive, yAxisActive) {
    @Override
    protected void dataItemAdded(XYChart.Series<String,Number> series, int itemIndex, XYChart.Data<String,Number> item) {
        super.dataItemAdded(series, itemIndex, item);

        Node bar = item.getNode();
        double barVal = item.getYValue().doubleValue();

        if (barVal < 0) {
            bar.getStyleClass().add("negative");
        }   
    }       
};