为什么在将事件添加到每个饼图切片后，JavaFX PieChart标签不显示？(Why does JavaFX PieChart label not show after after adding Events to each pie slice? (Java 8))

 我正在学习本教程（底部的部分称为“处理饼图的鼠标事件”）： 
 
 https://docs.oracle.com/javase/8/javafx/user-interface-tutorial/pie-chart.htm 
 
 我的代码如下： 
 
@FXML
public void initialize() {
    pieChart.setTitle("Breakdown of Customers by City");
    pieChart.setLegendSide(Side.LEFT);

    final Task<ObservableList<PieChart.Data>> task = new NumClientsAtLocationTask(new CustomerAccountDaoSelect());
    new Thread(task).start();
    task.setOnSucceeded(ae -> {

        pieChart.setData(task.getValue());

        final Label caption = new Label("");
        caption.setTextFill(Color.DARKORANGE);
        caption.setStyle("-fx-font: 24 arial;");

        for (final PieChart.Data data : pieChart.getData()) {
            data.getNode().addEventHandler(MouseEvent.MOUSE_PRESSED,
                    ae2 -> {
                        caption.setTranslateX(ae2.getSceneX());
                        caption.setTranslateY(ae2.getSceneY());
                        caption.setText(String.valueOf(data.getPieValue()));
                    });
        }
    });

}


class NumClientsAtLocationTask extends Task<ObservableList<PieChart.Data>> {
    private DaoSelect<CustomerAccount> customerAccountDaoSelect;

    NumClientsAtLocationTask(DaoSelect<CustomerAccount> customerAccountDaoSelect) {
        this.customerAccountDaoSelect = customerAccountDaoSelect;
    }

    @Override
    protected ObservableList<PieChart.Data> call() throws Exception {
        List<CustomerAccount> customerAccounts = customerAccountDaoSelect.select(RunListeners.FALSE);

        Map<String, List<CustomerAccount>> customerMap =
                customerAccounts
                        .stream()
                        .collect(Collectors.groupingBy(CustomerAccount::getCity));

        int london = customerMap.get("London").size();
        int phoenix = customerMap.get("Phoenix").size();
        int newYork = customerMap.get("New York").size();

        ObservableList<PieChart.Data> results = FXCollections.observableArrayList(
                new PieChart.Data("London", london),
                new PieChart.Data("Phoenix", phoenix),
                new PieChart.Data("New York", newYork));

        updateValue(results);
        return results;
    }
}
 
 图表以默认形式显示正常，但是当我在切片上单击鼠标时，标签不会出现。 如果我将标签打印到控制台，它会显示正确的值，它不会像在教程中那样显示在屏幕上。 有任何想法吗？ 

I'm following this tutorial (the section at the bottom called "Processing Mouse Events for a Pie Chart"): 
 
https://docs.oracle.com/javase/8/javafx/user-interface-tutorial/pie-chart.htm
 
And my code is as follows:
 
@FXML
public void initialize() {
    pieChart.setTitle("Breakdown of Customers by City");
    pieChart.setLegendSide(Side.LEFT);

    final Task<ObservableList<PieChart.Data>> task = new NumClientsAtLocationTask(new CustomerAccountDaoSelect());
    new Thread(task).start();
    task.setOnSucceeded(ae -> {

        pieChart.setData(task.getValue());

        final Label caption = new Label("");
        caption.setTextFill(Color.DARKORANGE);
        caption.setStyle("-fx-font: 24 arial;");

        for (final PieChart.Data data : pieChart.getData()) {
            data.getNode().addEventHandler(MouseEvent.MOUSE_PRESSED,
                    ae2 -> {
                        caption.setTranslateX(ae2.getSceneX());
                        caption.setTranslateY(ae2.getSceneY());
                        caption.setText(String.valueOf(data.getPieValue()));
                    });
        }
    });

}


class NumClientsAtLocationTask extends Task<ObservableList<PieChart.Data>> {
    private DaoSelect<CustomerAccount> customerAccountDaoSelect;

    NumClientsAtLocationTask(DaoSelect<CustomerAccount> customerAccountDaoSelect) {
        this.customerAccountDaoSelect = customerAccountDaoSelect;
    }

    @Override
    protected ObservableList<PieChart.Data> call() throws Exception {
        List<CustomerAccount> customerAccounts = customerAccountDaoSelect.select(RunListeners.FALSE);

        Map<String, List<CustomerAccount>> customerMap =
                customerAccounts
                        .stream()
                        .collect(Collectors.groupingBy(CustomerAccount::getCity));

        int london = customerMap.get("London").size();
        int phoenix = customerMap.get("Phoenix").size();
        int newYork = customerMap.get("New York").size();

        ObservableList<PieChart.Data> results = FXCollections.observableArrayList(
                new PieChart.Data("London", london),
                new PieChart.Data("Phoenix", phoenix),
                new PieChart.Data("New York", newYork));

        updateValue(results);
        return results;
    }
}
 
The chart shows fine in its default form, but when I click the mouse on a slice, the label doesn't appear. If I print the label to console, it shows the correct value, it's just not showing up on screen like in the tutorial. Any ideas?

原文：https://stackoverflow.com/questions/43969193