Question

我目前正在尝试使用javafx / fxml为学校项目创建一个基本的省钱计划，所以我还在学习。我目前正在尝试设置一种方法，当用户关闭程序时，它会运行一些代码来保存当前显示在textField endGoal中的值。问题是控制器中的Textfield不断抛出NullPointException。反正是否取消它或修复它？第endGoal.setText("This is fake.");行问题。

控制器：

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：

 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)

Answer 1

尝试替换

Parent root = FXMLLoader.load(getClass().getResource("MainPage.fxml"));

通过

FXMLLoader loader = new FXMLLoader(getClass().getResource("MainPage.fxml"));
loader.setController(this);
Parent root = loader.load();

你必须这样做的原因是FXMLLoader将创建fxml文件中指定的控制器类的新实例，因为它无法知道这样的对象是否已经存在。但是，您可以通过setController（）方法指定一个对象，该方法将填充您的fxml GUI元素。

Javafx / Fxml - 尝试在程序关闭

1 个答案: