我正在使用JavaFX，问题是当在XYChart中训练绘制新行时，出现错误NullPointerException。创建新的窗格后，它会变亮。 Secont Pane正在以折线图打开，但为空。我从以下代码的这一行得到错误。
lineChart.getData().addAll(series);
当我尝试在主窗口中执行此操作时，一切正常，并且线条绘制正确。但是，当我在创建第二个窗格后尝试执行此操作时，出现错误NullPointerException。
代码片段向我发送错误：
chartsButton.setOnAction(new EventHandler<ActionEvent>() {
@SuppressWarnings("unchecked")
@Override
public void handle(ActionEvent event) {
Parent chartParent;
try {
Stage chartsWindow = new Stage();
chartParent = FXMLLoader.load(getClass().getResource("/eng/gascalculator/view/ChartsPane.fxml"));
chartsWindow.setTitle("Charts");
chartsWindow.setScene(new Scene(chartParent, 450, 450));
chartsWindow.show();
} catch (IOException e) {
}
XYChart.Series<String, Number> series = new XYChart.Series<String, Number>();
series.getData().add(new XYChart.Data<String, Number>("Jan", 10));
series.getData().add(new XYChart.Data<String, Number>("Feb", 30));
lineChart.getData().addAll(series);
}
});
它的工作原理是，当我单击图表按钮时，新窗格应打开，其中包含图表线和图表上的数据。
我认为这将是一个新的单独实例的问题，例如@Slaw tell。下面，我用最少的代码准备新程序。我有2个fxml文件都已将刺客控制到MainController类。 MainPane打开正确，但是当我按下按钮打开带有图表的第二个窗格时，我得到信息，lineChart为空。
MainConntroller类：
package application;
import java.io.IOException;
import java.net.URL;
import java.util.ResourceBundle;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.chart.LineChart;
import javafx.scene.chart.XYChart;
import javafx.scene.control.Button;
import javafx.stage.Stage;
public class MainController implements Initializable {
@FXML
private Button chartButton;
@FXML
private LineChart<String, Number> lineChart;
@Override
public void initialize(URL location, ResourceBundle resources) {
chartButton.setOnAction(new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent event) {
Parent chartParent;
try {
Stage chartsWindow = new Stage();
chartParent = FXMLLoader.load(getClass().getResource("/application/ChartPane.fxml"));
chartsWindow.setTitle("Charts");
chartsWindow.setScene(new Scene(chartParent, 450, 450));
chartsWindow.show();
} catch (IOException e) {
}
XYChart.Series<String, Number> series = new XYChart.Series<String, Number>();
series.getData().add(new XYChart.Data<String, Number>("Jan", 10));
series.getData().add(new XYChart.Data<String, Number>("Feb", 30));
lineChart.getData().addAll(series);
}
});
}
}
主类：
package application;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.stage.Stage;
import javafx.scene.Parent;
import javafx.scene.Scene;
public class Main extends Application {
@Override
public void start(Stage stage) throws Exception {
Parent parent = FXMLLoader.load(getClass().getResource("/application/MainPane.fxml"));
Scene scene = new Scene(parent);
stage.setScene(scene);
stage.setTitle("First window");
stage.show();
}
public static void main(String[] args) {
launch(args);
}
}
MainPane.fxml文件：
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.layout.AnchorPane?>
<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity"
minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0"
xmlns="http://javafx.com/javafx/10.0.1"
xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.MainController">
<children>
<Button fx:id="chartButton" layoutX="265.0" layoutY="188.0"
mnemonicParsing="false" text="Chart" />
</children>
ChartPane.fxml文件：
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.chart.CategoryAxis?>
<?import javafx.scene.chart.LineChart?>
<?import javafx.scene.chart.NumberAxis?>
<?import javafx.scene.layout.AnchorPane?>
<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity"
minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0"
xmlns="http://javafx.com/javafx/10.0.1"
xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.MainController">
<children>
<LineChart fx:id="lineChart" layoutX="50.0">
<xAxis>
<CategoryAxis side="BOTTOM" />
</xAxis>
<yAxis>
<NumberAxis side="LEFT" />
</yAxis>
</LineChart>
</children>
</AnchorPane>