错误：线程"JavaFX Application Thread"中的异常 java.lang.NullPointerException：无法调用"application.Controller.move

Question

我在JavaFX应用程序中收到这个错误。如果你知道如何解决它。请帮助我：(

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException: Cannot invoke "application.Controller.moveUp()" because "this.val$controller" is null
at KeyEvent/application.Main$1.handle(Main.java:33)
at KeyEvent/application.Main$1.handle(Main.java:1)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Scene$KeyHandler.process(Scene.java:4105)
at javafx.graphics/javafx.scene.Scene.processKeyEvent(Scene.java:2156)
at javafx.graphics/javafx.scene.Scene$ScenePeerListener.keyEvent(Scene.java:2630)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(GlassViewEventHandler.java:218)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(GlassViewEventHandler.java:150)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleKeyEvent$1(GlassViewEventHandler.java:250)
at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleKeyEvent(GlassViewEventHandler.java:249)
at javafx.graphics/com.sun.glass.ui.View.handleKeyEvent(View.java:548)
at javafx.graphics/com.sun.glass.ui.View.notifyKey(View.java:972)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
at java.base/java.lang.Thread.run(Thread.java:833)

我的代码：

package application;


import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.fxml.FXMLLoader;
import javafx.stage.Stage;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.input.KeyEvent;



public class Main extends Application {
@Override
public void start(Stage stage) {
try {
FXMLLoader loader = new FXMLLoader(getClass().getResource("Scene.fxml"));
Parent root = loader.load();
Controller controller = loader.getController();
Scene scene = new Scene(root);

scene.setOnKeyPressed(new EventHandler<KeyEvent>() {



@Override
public void handle(KeyEvent event) {
//System.out.println(event.getCode());
//if I write -> if(controller != null) it doesn't work
switch(event.getCode()) {
case UP:
controller.moveUp();
break;
case DOWN:
controller.moveDown();
break;
case LEFT:
controller.moveLeft();
break;
case RIGHT:
controller.moveRight();
break;
default:
break;

}
}

});

stage.setScene(scene);
stage.show();

} catch(Exception e) {
e.printStackTrace();
}

}

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

控制器：

package application;

public class Controller {

public void moveUp() {
System.out.println("UP");
}

public void moveDown() {
System.out.println("DOWN");
}

public void moveLeft() {
System.out.println("LEFT");
}

public void moveRight() {
System.out.println("RIGHT");
}

}

Answer 1

异常状态：

because "this.val$controller" is null

要设置控制器，请执行以下操作之一：

1. 在调用load之前，在fxml加载程序实例上显式调用setController

   或

2. 在FXML中定义fx:controller属性。