How to display values in JavaFX Pie Chart?

Question

I am displaying pie chart representing under and over performing students for each module of a degree. The code that I have displays this: output

However I would like the values for each slice to appear within it, I don't want any fancy mouselistener thing just to show the numbers in the slices.

My code is as follows:

public class PieChartSample extends Application { //TODO make constructor that takes hashmaps as arguments
static Map<String, Integer> studsabove = new HashMap<String, Integer>();
static Map<String, Integer> studsbelow = new HashMap<String, Integer>();

@Override
public void start(Stage primaryStage) throws Exception {
    primaryStage.setTitle("My First JavaFX App");

    ArrayList<PieChart> pielist = new ArrayList<PieChart>();
    for(Entry<String, Integer> mod: studsabove.entrySet()){
        for(Entry<String, Integer> mod2: studsbelow.entrySet()){
            PieChart pieChart = new PieChart();
            PieChart.Data above = new PieChart.Data(mod.getKey(), mod.getValue());
            PieChart.Data below = new PieChart.Data(mod2.getKey(), mod2.getValue());

            pieChart.getData().add(above);
            pieChart.getData().add(below);

            pielist.add(pieChart);
        }
    }

    VBox vbox = new VBox();
    for (PieChart pie: pielist){
        pie.setLabelLineLength(10); //FIXME
        pie.setLegendSide(Side.LEFT);
        vbox.getChildren().add(pie);
    }
    Scene scene = new Scene(vbox, 400, 200); //TODO: Make pie charts appear horizontally rather than vertically

    primaryStage.setScene(scene);
    primaryStage.setHeight(900);
    primaryStage.setWidth(400);

    primaryStage.show();
}


public static void main(String[] args) { //TODO: need to figure out how to display the values in the slices of the pie charts

    PieChartSample.studsabove.put("CE201", 23);
    PieChartSample.studsbelow.put("CE201", 67);

    PieChartSample.studsabove.put("CE222", 20);
    PieChartSample.studsbelow.put("CE222", 80);


    PieChartSample.studsabove.put("CE233", 6);
    PieChartSample.studsbelow.put("CE233", 94);

    PieChartSample.studsabove.put("CE244", 56);
    PieChartSample.studsbelow.put("CE244", 44);
    Application.launch(args);
}

}

Answer 1

You can extend PieChart like this:

import java.util.HashMap;
import java.util.Map;
import javafx.collections.ListChangeListener;
import javafx.scene.chart.PieChart;
import javafx.scene.layout.Region;
import javafx.scene.shape.Arc;
import javafx.scene.text.Text;

public class LabeledPieChart extends PieChart {

    private final Map<Data, Text> _labels = new HashMap<>();

    public LabeledPieChart() {
        super();
        this.getData().addListener((ListChangeListener.Change<? extends Data> c) -> {
            addLabels();
        });

    }

    @Override
    protected void layoutChartChildren(double top, double left, double contentWidth, double contentHeight) {
        super.layoutChartChildren(top, left, contentWidth, contentHeight);

        double centerX = contentWidth / 2 + left;
        double centerY = contentHeight / 2 + top;

        layoutLabels(centerX, centerY);
    }

    private void addLabels() {

        for (Text label : _labels.values()) {
            this.getChartChildren().remove(label);
        }
        _labels.clear();
        for (Data vData : getData()) {
            final Text dataText;
            final double yValue = vData.getPieValue();
            dataText = new Text(Double.toString(yValue));
            _labels.put(vData, dataText);
            this.getChartChildren().add(dataText);
        }
    }

    private void layoutLabels(double centerX, double centerY) {

        double total = 0.0;
        for (Data d : this.getData()) {
            total += d.getPieValue();
        }
        double scale = (total != 0) ? 360 / total : 0;

        for (Map.Entry<Data, Text> entry : _labels.entrySet()) {
            Data vData = entry.getKey();
            Text vText = entry.getValue();

            Region vNode = (Region) vData.getNode();
            Arc arc = (Arc) vNode.getShape();

            double start = arc.getStartAngle();

            double size = (isClockwise()) ? (-scale * Math.abs(vData.getPieValue())) : (scale * Math.abs(vData.getPieValue()));
            final double angle = normalizeAngle(start + (size / 2));
            final double sproutX = calcX(angle, arc.getRadiusX() / 2, centerX);
            final double sproutY = calcY(angle, arc.getRadiusY() / 2, centerY);

            vText.relocate(
                    sproutX - vText.getBoundsInLocal().getWidth(),
                    sproutY - vText.getBoundsInLocal().getHeight());
        }

    }

    private static double normalizeAngle(double angle) {
        double a = angle % 360;
        if (a <= -180) {
            a += 360;
        }
        if (a > 180) {
            a -= 360;
        }
        return a;
    }

    private static double calcX(double angle, double radius, double centerX) {
        return (double) (centerX + radius * Math.cos(Math.toRadians(-angle)));
    }

    private static double calcY(double angle, double radius, double centerY) {
        return (double) (centerY + radius * Math.sin(Math.toRadians(-angle)));
    }

}

And here is a main class for you to test:

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.chart.PieChart.Data;
import javafx.scene.layout.AnchorPane;
import javafx.stage.Stage;

public class JavaFXApplication28 extends Application {

    @Override
    public void start(Stage stage) {

        stage.setTitle("Imported Fruits");
        stage.setWidth(500);
        stage.setHeight(500);

        LabeledPieChart chart = new LabeledPieChart();
        chart.setTitle("Imported Fruits");

        // Add some data
        addPieChartData(chart, "Grapefruit", 13);
        addPieChartData(chart, "Oranges", 25);
        addPieChartData(chart, "Plums", 10);
        addPieChartData(chart, "Pears", 22);
        addPieChartData(chart, "Apples", 30);

        AnchorPane anchor = new AnchorPane();
        Scene scene = new Scene(anchor);
        anchor.getChildren().add(chart);

        AnchorPane.setBottomAnchor(chart, 0.0);
        AnchorPane.setTopAnchor(chart, 0.0);
        AnchorPane.setLeftAnchor(chart, 0.0);
        AnchorPane.setRightAnchor(chart, 0.0);

        stage.setScene(scene);
        stage.show();
    }

    public void addPieChartData(LabeledPieChart pChart, String name, double value) {
        final Data data = new Data(name, value);
        pChart.getData().add(data);
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        launch(args);
    }

}