PieChart在javaFX中不起作用

Question

在下面给出的代码中，我想在点击提交按钮时显示饼图。它没有显示任何错误，但甚至没有显示饼图。我已经静态地为我的fxml代码添加了一个条形图，并在点击按钮后在饼图中显示详细信息。

这是我的java代码

import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.chart.BarChart;
import javafx.scene.chart.CategoryAxis;
import javafx.scene.chart.NumberAxis;
import javafx.scene.chart.PieChart;
import javafx.scene.chart.XYChart;
import javafx.scene.control.Button;
import javafx.scene.control.ComboBox;
import javafx.scene.layout.Pane;
import javax.naming.ldap.InitialLdapContext;
public class Operations implements  Initializable{

public Button buttonsubmit;
public PieChart piechart;
public Pane pane1,pane2;
public BarChart barchart;
public ComboBox combobox;
Connection con;
public void combo(ActionEvent e)
{

}
@FXML
private  void handleOnPieChartAction()
{

    try 
    {
        System.out.println("You clicked the Pie Chart!");
        piechart=new PieChart();
        ObservableList<PieChart.Data> pieChartData = FXCollections.observableArrayList( 
           new PieChart.Data("Negative", 45), 
           new PieChart.Data("Positive", 55));
        piechart.setData(pieChartData);
        System.out.println("You clicked the Pie Chart2!");
        piechart.setVisible(true);
    }
    catch (Exception e1) 
    {
    // TODO: handle exception
    }
}

@Override
public void initialize(URL location, ResourceBundle resources) 
{

    // TODO Auto-generated method stub
    buttonsubmit.setOnAction(new EventHandler<ActionEvent>() 
    {

         @Override
         public void handle(ActionEvent event) {
           // TODO Auto-generated method stub
           handleOnPieChartAction();

          }
         });
    }
}

我的FXML文件

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.chart.BarChart?>
<?import javafx.scene.chart.CategoryAxis?>
<?import javafx.scene.chart.NumberAxis?>
<?import javafx.scene.chart.PieChart?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.ComboBox?>
<?import javafx.scene.control.Menu?>
<?import javafx.scene.control.MenuBar?>
<?import javafx.scene.control.MenuItem?>
<?import javafx.scene.control.SeparatorMenuItem?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.layout.Pane?>
<?import javafx.scene.layout.VBox?>

<VBox prefHeight="900.0" prefWidth="900.0" xmlns="http://javafx.com/javafx/9" xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.Operations">

  <children>
    <MenuBar VBox.vgrow="NEVER">
      <menus>
        <Menu mnemonicParsing="false" text="File">
          <items>
            <MenuItem mnemonicParsing="false" text="New" />
            <MenuItem mnemonicParsing="false" text="Open…" />
            <Menu mnemonicParsing="false" text="Open Recent" />
            <SeparatorMenuItem mnemonicParsing="false" />
            <MenuItem mnemonicParsing="false" text="Close" />
            <MenuItem mnemonicParsing="false" text="Save" />
            <MenuItem mnemonicParsing="false" text="Save As…" />
            <MenuItem mnemonicParsing="false" text="Revert" />
            <SeparatorMenuItem mnemonicParsing="false" />
            <MenuItem mnemonicParsing="false" text="Preferences…" />
            <SeparatorMenuItem mnemonicParsing="false" />
            <MenuItem mnemonicParsing="false" text="Quit" />
          </items>
        </Menu>
        <Menu mnemonicParsing="false" text="Edit">
          <items>
            <MenuItem mnemonicParsing="false" text="Undo" />
            <MenuItem mnemonicParsing="false" text="Redo" />
            <SeparatorMenuItem mnemonicParsing="false" />
            <MenuItem mnemonicParsing="false" text="Cut" />
            <MenuItem mnemonicParsing="false" text="Copy" />
            <MenuItem mnemonicParsing="false" text="Paste" />
            <MenuItem mnemonicParsing="false" text="Delete" />
            <SeparatorMenuItem mnemonicParsing="false" />
            <MenuItem mnemonicParsing="false" text="Select All" />
            <MenuItem mnemonicParsing="false" text="Unselect All" />
          </items>
        </Menu>
        <Menu mnemonicParsing="false" text="Help">
          <items>
            <MenuItem mnemonicParsing="false" text="About MyHelloApp" />
          </items>
        </Menu>
      </menus>
    </MenuBar>
    <AnchorPane maxHeight="-1.0" maxWidth="-1.0" prefHeight="-1.0" prefWidth="-1.0" VBox.vgrow="ALWAYS">
      <children>
            <Pane layoutY="4.0" prefHeight="227.0" prefWidth="200.0">
               <children>
                  <ComboBox fx:id="combobox" layoutX="23.0" layoutY="23.0" onAction="#combo" prefWidth="150.0" />
               </children>
            </Pane>
            <Pane layoutY="205.0" prefHeight="200.0" prefWidth="200.0">
               <children>
                  <Button fx:id="buttonsubmit" layoutX="58.0" layoutY="100.0" mnemonicParsing="false"  text="submit" />
                  <TextField layoutX="15.0" layoutY="44.0" />
               </children>
            </Pane>
            <Pane fx:id="pane1" layoutX="345.0" layoutY="22.0" prefHeight="302.0" prefWidth="342.0">
               <children>
                  <BarChart fx:id="barchart" layoutX="2.0" layoutY="-1.0" prefHeight="315.0" prefWidth="342.0">
                    <xAxis>
                      <CategoryAxis side="BOTTOM" />
                    </xAxis>
                    <yAxis>
                      <NumberAxis side="LEFT" />
                    </yAxis>
                  </BarChart>
               </children></Pane>
            <Pane fx:id="pane2" layoutX="354.0" layoutY="373.0" prefHeight="315.0" prefWidth="342.0">
               <children>
                  <PieChart fx:id="piechart" layoutX="34.0" layoutY="29.0" prefHeight="221.0" prefWidth="259.0" />
               </children></Pane>
      </children>
    </AnchorPane>
  </children>
</VBox>

饼图显示什么.. 知道为什么它不起作用......