JavaFX通过FXML创建BarChart报错：无法实例化该组件

错误根源 #

• BarChart没有公共无参构造方法，FXML无法直接创建空实例，必须传入x轴和y轴参数。
• Controller中同时使用@FXML注解和手动new BarChart<>(xAxis, yAxis)，导致FXML注入与手动实例化冲突。

修复步骤 #

1. 修改FXML文件，定义坐标轴并关联BarChart #

在FXML中添加坐标轴组件，通过属性绑定将其传入BarChart：

<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.geometry.Insets?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.layout.VBox?>
<?import javafx.event.ActionEvent?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.ComboBox?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.control.TextField?>
<?import javafx.collections.ListChangeListener.Change?>

<?import javafx.scene.chart.BarChart?>
<?import javafx.scene.chart.CategoryAxis?>
<?import javafx.scene.chart.NumberAxis?>

<GridPane hgap="15" vgap="15" xmlns="http://javafx.com/javafx/16" xmlns:fx="http://javafx.com/fxml/1" fx:controller="com.example.demo.HelloController">
    <ComboBox fx:id="fromCurrency" onAction="#changeFromCurrencyCombo" GridPane.rowIndex="3" GridPane.columnIndex="2"/>
    <TextField fx:id="fromCurrencyText" onTextChange="#changeFromCurrencyText" GridPane.rowIndex="4" GridPane.columnIndex="2"/>
    <Label fx:id="fromCurrencyLabel" GridPane.rowIndex="5" GridPane.columnIndex="2"></Label>
    <Button fx:id="swapButton" text="↔" GridPane.rowIndex="6" GridPane.columnIndex="2" onAction="#swapButtonClicked"></Button>
    <ComboBox fx:id="toCurrency" onAction="#changeToCurrencyCombo" GridPane.rowIndex="7" GridPane.columnIndex="2"/>
    <Label fx:id="toCurrencyText"  GridPane.rowIndex="8" GridPane.columnIndex="2"/><!--onTextChange="#changeToCurrencyText"-->
    <Label fx:id="toCurrencyLabel" GridPane.rowIndex="9" GridPane.columnIndex="2"></Label>
    
    <!-- 定义坐标轴 -->
    <CategoryAxis fx:id="xAxis" GridPane.rowIndex="10" GridPane.columnIndex="2"/>
    <NumberAxis fx:id="yAxis" GridPane.rowIndex="10" GridPane.columnIndex="2"/>
    
    <!-- 绑定坐标轴到BarChart -->
    <BarChart fx:id="chart" 
              xAxis="$xAxis" 
              yAxis="$yAxis" 
              GridPane.rowIndex="10" 
              GridPane.columnIndex="2"/>
</GridPane>

2. 修改Controller代码，移除手动实例化逻辑 #

去掉手动创建的BarChart、xAxis、yAxis，仅保留FXML注入的变量：

package com.example.demo;

import javafx.beans.value.ObservableValue;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
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.XYChart;
import javafx.scene.control.Button;
import javafx.scene.control.ComboBox;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;

import java.net.URL;
import java.util.List;
import java.util.ResourceBundle;


public class HelloController implements Initializable {
    @FXML
    public ComboBox fromCurrency;
    @FXML
    public ComboBox toCurrency;
    @FXML
    private Label fromCurrencyLabel;
    @FXML
    private Label toCurrencyLabel;
    @FXML
    private TextField fromCurrencyText;
    @FXML
    private Label toCurrencyText;
    public String currentFromCurrency = ""; //текущая валюта, из которой переводим
    public String currentToCurrency = ""; //текущая валюта, в которую переводим
    @FXML
    private ObservableList<String> items;
    @FXML
    private Button swapButton;
    @FXML
    private List<String> currencies;
    
    // 由FXML注入的坐标轴和图表
    @FXML
    private CategoryAxis xAxis;
    @FXML
    private NumberAxis yAxis;
    @FXML
    private BarChart<String,Number> chart;
    
    private boolean canChange = true;


    @Override
    public void initialize(URL location, ResourceBundle resources) {
        items = FXCollections.observableArrayList("Рубль", "Доллар", "Евро", "Злотый");
        fromCurrency.setItems(items);
        fromCurrency.setValue(items.get(0));
        currentFromCurrency = items.get(0);
        toCurrency.setItems(items);
        toCurrency.setValue(items.get(1));
        currentToCurrency = items.get(1);
        HelloParser par = new HelloParser();
        par.connect();
        currencies = par.getData();
        par.checkDate();
        drawChart();
    }

    public void drawChart() {
        chart.setTitle("Country Summary");
        xAxis.setLabel("Country");
        yAxis.setLabel("Value");

        XYChart.Series<String, Number> series1 = new XYChart.Series<>();
        series1.setName("2003");
        series1.getData().add(new XYChart.Data<>("Austria", 25601.34));
        series1.getData().add(new XYChart.Data<>("Brazil", 20148.82));
        series1.getData().add(new XYChart.Data<>("France", 10000));
        series1.getData().add(new XYChart.Data<>("Italy", 35407.15));
        series1.getData().add(new XYChart.Data<>("USA", 12000));

        XYChart.Series<String, Number> series2 = new XYChart.Series<>();
        series2.setName("2004");
        series2.getData().add(new XYChart.Data<>("Austria", 57401.85));
        series2.getData().add(new XYChart.Data<>("Brazil", 41941.19));
        series2.getData().add(new XYChart.Data<>("France", 45263.37));
        series2.getData().add(new XYChart.Data<>("Italy", 117320.16));
        series2.getData().add(new XYChart.Data<>("USA", 14845.27));

        XYChart.Series<String, Number> series3 = new XYChart.Series<>();
        series3.setName("2005");
        series3.getData().add(new XYChart.Data<>("Austria", 45000.65));
        series3.getData().add(new XYChart.Data<>("Brazil", 44835.76));
        series3.getData().add(new XYChart.Data<>("France", 18722.18));
        series3.getData().add(new XYChart.Data<>("Italy", 17557.31));
        series3.getData().add(new XYChart.Data<>("USA", 92633.68));
        
        chart.getData().addAll(series1, series2, series3);
    }
}

3. 额外优化说明 #

• 移除了非UI变量上错误的@FXML注解（如currentFromCurrency、items）。
• 给XYChart.Series添加泛型参数，消除未检查的编译警告。
• FXML中通过$xAxis、$yAxis引用已定义的坐标轴实例，满足BarChart的构造参数要求。

内容的提问来源于stack exchange，提问作者Kerby3