java Javafx/Fxml尝试在程序关闭时从外部保存值时出错
我目前正在尝试使用javafx/fxml为一个学校项目创建一个基本的省钱程序，所以我还在学习。我目前正在尝试设置一种方式，当用户关闭程序时，它会运行一些代码来保存文本字段endGoal中当前显示的值。问题是控制器中的Textfield一直抛出NullPointException。是否有任何方法可以取消它的空值或修复它？第endGoal.setText("This is fake.");行出现问题
控制员：
package sample;
import javafx.application.Platform;
import javafx.animation.*;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Node;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.TextField;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;
import java.io.*;
import java.io.FileReader;
import javafx.application.*;
import javax.annotation.PostConstruct;
public class MainPageController {
@FXML
private Button openPage1;
@FXML
private Button openPage2;
@FXML
private Button generateNewGoal;
@FXML
private Button resetGoal;
@FXML
private TextField moneySaved;
@FXML
private TextField currentGoal;
@FXML
public BorderPane BorderPane;
@FXML
public Stage myStage;
public void initialize() throws Exception{
FileReader reader = new FileReader("Goal.txt");
BufferedReader br = new BufferedReader(reader);
String goal = br.readLine();
currentGoal.setText(goal);
reader.close();
}
@PostConstruct
public void start(Stage stage1)throws Exception{
myStage = stage1;
FXMLLoader loader = new FXMLLoader(getClass().getResource("MainPage.fxml"));
Parent root = loader.load();
loader.getController();
loader.load();
loader.getController();
stage1.getScene().getWindow();
myStage.setOnCloseRequest(e -> onEnd());
}
public void openPage1(ActionEvent event) throws Exception {
FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("MandatoryCostCollector.fxml"));
Parent root = (Parent) fxmlLoader.load();
Stage stage = new Stage();
stage.setScene(new Scene(root));
stage.setTitle("Money Saver Program");
stage.show();
((Node) event.getSource()).getScene().getWindow().hide();
}
public void openPage2(ActionEvent event) throws Exception {
FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("PayDataCollector.fxml"));
Parent root = (Parent) fxmlLoader.load();
Stage stage = new Stage();
stage.setScene(new Scene(root));
stage.setTitle("Money Saver Program");
stage.show();
((Node) event.getSource()).getScene().getWindow().hide();
}
public void resetGoal(ActionEvent event) throws Exception {
currentGoal.setText("");
}}
public void saveData()throws Exception{
endGoal.setText("This is fake.");
FileWriter writer = new FileWriter("Goal.txt");
String goal = (endGoal.getText());
writer.write(goal);
writer.close();
}
主要问题：
package sample;
import com.sun.org.apache.xpath.internal.Arg;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.TextField;
import javafx.stage.Stage;
import jdk.nashorn.internal.runtime.regexp.joni.constants.Arguments;
import javax.xml.soap.Text;
import java.io.*;
import java.util.*;
public class Main extends Application {
@FXML
public TextField currentGoal;
File f = new File("Goal.txt");
public String finalGoal;
@Override
public void start(Stage primaryStage)throws Exception {
boolean bool = false;
if (f.exists() )
{
Parent root = FXMLLoader.load(getClass().getResource("MainPage.fxml"));
primaryStage.setTitle("Money Saver Program");
primaryStage.setScene(new Scene(root, 600, 400));
primaryStage.show();
}
else
{
bool = f.createNewFile();
Parent root = FXMLLoader.load(getClass().getResource("OpeningPage.fxml"));
primaryStage.setTitle("Money Saver Program");
primaryStage.setScene(new Scene(root, 638, 400));
primaryStage.show();
}
primaryStage.setOnCloseRequest(e -> closeProgram());
}
public static void main(String[] args) throws Exception {
launch(args);
}
public void closeProgram(){
Platform.exit();
}
public void stop()throws Exception{
mainPageController.saveData();
System.out.print("Goal has been saved!");
}
}
}
FXML：
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.text.*?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>
<BorderPane fx:id="BorderPane" maxHeight="-Infinity" maxWidth="- Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.MainPageController">
<top>
<VBox prefHeight="65.0" prefWidth="600.0" BorderPane.alignment="CENTER">
<children>
<TextField alignment="CENTER" editable="false" prefHeight="68.0" prefWidth="600.0" text="Welcome to the Money Saving Program">
<font>
<Font name="Arial Rounded MT Bold" size="26.0" />
</font>
</TextField>
</children>
</VBox>
</top>
<left>
<VBox prefHeight="335.0" prefWidth="159.0" BorderPane.alignment="CENTER">
<children>
<Button fx:id="openPage1" mnemonicParsing="false" onAction="#openPage1" prefHeight="88.0" prefWidth="167.0" text="1. Open Mandatory Cost Collector" wrapText="true">
<font>
<Font name="Arial" size="18.0" />
</font>
</Button>
<Button fx:id="openPage2" mnemonicParsing="false" onAction="#openPage2" prefHeight="60.0" prefWidth="173.0" text="2. Open Pay Data Collector" wrapText="true">
<font>
<Font name="Arial" size="18.0" />
</font>
</Button>
</children>
</VBox>
</left>
<right>
<VBox prefHeight="335.0" prefWidth="166.0" BorderPane.alignment="CENTER">
<children>
<TextField fx:id="endGoal" promptText="\$">
<font>
<Font name="Arial" size="40.0" />
</font>
</TextField>
<Button fx:id="resetGoal" contentDisplay="RIGHT" mnemonicParsing="false" onAction="#resetGoal" prefHeight="33.0" prefWidth="173.0" text="Reset Goal" wrapText="true">
<font>
<Font name="Arial" size="18.0" />
</font>
</Button>
</children>
</VBox>
</right>
<bottom>
<HBox prefHeight="100.0" prefWidth="200.0" BorderPane.alignment="CENTER">
<children>
<Button fx:id="generateNewGoal" mnemonicParsing="false" prefHeight="63.0" prefWidth="161.0" text="3. Generate your new goal" translateY="36.0" wrapText="true">
<font>
<Font name="Arial" size="18.0" />
</font>
</Button>
<TextField alignment="CENTER" editable="false" prefHeight="75.0" prefWidth="221.0" text="Money saved this week" translateX="38.0" translateY="23.0">
<font>
<Font name="Arial" size="18.0" />
</font>
</TextField>
<TextField fx:id="moneySaved" editable="false" prefHeight="75.0" prefWidth="180.0" promptText="\$" translateX="38.0" translateY="23.0">
<font>
<Font name="Arial" size="40.0" />
</font>
</TextField>
</children>
</HBox>
</bottom>
<center>
<VBox prefHeight="200.0" prefWidth="100.0" BorderPane.alignment="CENTER">
<children>
<TextField editable="false" maxHeight="-Infinity" maxWidth="-Infinity" prefHeight="68.0" prefWidth="167.0" text="Your current goal" translateX="108.0">
<font>
<Font name="Arial" size="18.0" />
</font>
</TextField>
</children>
</VBox>
</center>
</BorderPane>
错误：
Exception in Application stop method
Exception in thread "main" java.lang.RuntimeException: Exception in Application stop method
at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:922)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$155(LauncherImpl.java:182)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
at sample.MainPageController.saveData(MainPageController.java:99)
at sample.Main.stop(Main.java:73)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$163(LauncherImpl.java:882)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$175(PlatformImpl.java:326)
at com.sun.javafx.application.PlatformImpl.lambda$null$173(PlatformImpl.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$174(PlatformImpl.java:294)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
# 1 楼答案
试着替换
借
必须执行此操作的原因是，FXMLLoader将创建fxml文件中指定的控制器类的新实例，因为它无法知道此类对象是否已经存在。但是，您可以通过setController（）方法指定对象，该方法将使用fxml GUI元素填充