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JavaFX打开一个新的场景

 2023-02-16    390  

问题描述

我希望我的代码工作，以便当我单击按钮时，将打开一个新场景，但它不起作用，我不知道为什么.

public void start(Stage primaryStage) throws Exception {
    window = primaryStage;

    Parent root = FXMLLoader.load(getClass().getResource("FXML/LoginScene.fxml"));
    scene = new Scene(root,400,400);
    openScene = new OpenScene(writer);
    window.setScene(scene);
    window.show();


}
public static void main(String[] args){
    launch(args);
}
@FXML protected void btnConnect(ActionEvent event) {
    System.out.println("hallo");
    try {
    openScene.start(window);    } catch (Exception e) {

        e.printStackTrace();
    }
}

GUI成功出现，但是当我按按钮时，它会引发异常.

JavaFX打开一个新的场景

public class OpenScene extends Application{
    PrintWriter writer;

    @Override
    public void start(Stage window) throws Exception {
        Parent root = FXMLLoader.load(getClass().getResource("FXML/OpenScene.fxml"));
        Scene scene =  new Scene(root, 200 ,200);
        window.setScene(scene);
        window.show();

    }
    public OpenScene(PrintWriter writer){
        this.writer = writer;
    }
}

更新

我尝试将应用程序类与詹姆斯_D的答案中的控制器类分开，但是我得到了以下例外:

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1762)
at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1645)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Node.fireEvent(Node.java:8216)
at javafx.scene.control.Button.fire(Button.java:185)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3724)
at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3452)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1728)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2461)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:348)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:273)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:382)
at com.sun.glass.ui.View.handleMouseEvent(View.java:553)
at com.sun.glass.ui.View.notifyMouse(View.java:925)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1759)
... 43 more
Caused by: java.lang.NullPointerException
at MainController.btnConnect(MainController.java:22)
... 53 more

推荐答案

看起来您正在尝试将主应用程序类用作控制器类.这将令人困惑，您应该避免它.这是发生的事情:

启动应用程序时，它会调用launch(…).从Application继承的launch方法将执行一堆重要的”家政人员”，例如启动Javafx工具包和Javafx应用程序线程.然后，它创建您的应用程序子类的实例，创建一个初始Stage并在该实例中调用start(…).

在您的start(…)方法中，您初始化了几个实例变量(window和openScene)，并加载了一个FXML文件，显示其内容. FXMLLoader.load(…)方法执行以下操作:

  • 根据文件中的XML元素创建UI元素
  • 创建一个由FXML文件中fx:controller属性指定的类的实例
  • 将任何@FXML通知字段注入控制器实例
  • 注册FXML文件中指定的任何事件处理程序

请注意，如果您为应用程序和控制器指定同一类，则将创建该类的两个实例.一个是由launch方法创建的，一个由FXMLLoader创建.请注意，只有通过launch方法创建的实例才能调用start(…)方法.由于您在start(…)方法中初始化了实例变量，因此这些变量未在FXMLLoader创建的实例中初始化.因此，在由FXMLLoader创建的实例中(如果愿意，”控制器实例”，window和openScene未初始化.因此线

openScene.start(window);

会扔NullPointerException.

由于应用程序和控制器确实具有完全不同的角色，因此您应该将它们分为不同的类.这将使事情变得不那么混乱.请注意，您始终可以通过调用

来找到显示节点的窗口

anyNode.getScene().getWindow();

因此，无需缓存Stage实例.

so:

public class MainApp extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception {

        // change LoginScene.fxml so it now has fx:controller="LoginController"
        Parent root = FXMLLoader.load(getClass().getResource("FXML/LoginScene.fxml"));

        Scene scene = new Scene(root, 400, 400);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

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

并为控制器使用其他类:

public class LoginController {

    private OpenScene openScene ;

    @FXML
    private Button connectButton ; // needs fx:id in fxml file...

    public void initialize() throws Exception {
        PrintWriter writer = ... ;
        openScene = new OpenScene(writer);
    }

    @FXML // handler for connect button:
    private void btnConnect() throws Exception {
        Stage stage = (Stage) connectButton.getScene().getWindow();
        openScene.start(stage);
    }
}

在

public class OpenScene {

    private final PrintWriter writer ;

    public OpenScene(PrintWriter writer) {
        this.writer = writer ;
    }

    // doesn't need to be called "start" any more...    
    public void start(Stage window) throws Exception {
        Parent root = FXMLLoader.load(getClass().getResource("FXML/OpenScene.fxml"));
        Scene scene =  new Scene(root, 200 ,200);
        window.setScene(scene);
        window.show();
    }
}

以上所述是小编给大家介绍的JavaFX打开一个新的场景,希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对77isp云服务器技术网的支持！

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