javaFX，抛出NullPointerException，位置必填 [英] javaFX, throws NullPointerException, Location is required

问题描述

我看到了其他答案，但没有任何帮助

i have seen other answers but nothing have helped me

(对不起，GUI的新知识只知道swing的基础知识)

(sorry new to GUI only know basics of swing)

这是主要班级

package application;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;


public class Main extends Application {
@Override
public void start(Stage primaryStage) {
    try {
Parent root=FXMLLoader.load(getClass().getClassLoader().getResource("/Main.fxml"));

  Scene scene = new Scene(root,400,400);
        scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
        primaryStage.setScene(scene);
        primaryStage.show();
    } 

    catch(Exception e) {
        e.printStackTrace();
        System.exit(0);

    }
}

public static void main(String[] args) {
    launch(args);
}
}

这是我要调用其方法的另一个类

this is another class whose method i want to invoke

package application;


import java.util.Random;
import javafx.event.ActionEvent;

import javafx.fxml.FXML;
import javafx.scene.control.Label;


public class MainController {

@FXML
private Label myMessage;
void generaterandom (ActionEvent event){
    Random rand=new Random();
    int myrand=rand.nextInt(50)+1;
    myMessage.setText(Integer.toString(myrand));
    System.out.println(Integer.toString(myrand));


}

}

如果需要，我将添加xml文件.

i will add xml file if needed .

这是我遇到的错误

java.lang.NullPointerException: Location is required.
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3207)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3175)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3148)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3124)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3104)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:3097)
at application.Main.start(Main.java:14)
at     com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$162(LauncherImpl    .java:863)
    at     com.sun.javafx.application.PlatformImpl.lambda$runAndWait$175(PlatformImpl.java:32    6)
    at     com.sun.javafx.application.PlatformImpl.lambda$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)

推荐答案

getClass().getClassLoader().getResource(...)将从相对于类路径的路径加载资源.由于您已将FXML文件放置在application pacakge中，因此需要:

getClass().getClassLoader().getResource(...) will load a resource from a path relative to the classpath. Since you placed the FXML file in the application pacakge, you need:

Parent root=FXMLLoader.load(getClass().getClassLoader().getResource("application/Main.fxml"));

如果仅使用getClass().getResource(...)，并且未在路径前添加/，它将从相对于当前类的路径加载.所以

If you just use getClass().getResource(...), and do not prefix the path with /, it will load from a path relative to the current class. So

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

也应该起作用.

确保将FXML文件和.class文件一起导出到构建文件夹.

Make sure that your FXML file is being exported to the build folder, along with the .class files.

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