java - 如何通过另一种方法与 JavaFX 类中的 PrimaryStage 进行交互？

Question

我目前正在测试一些 JavaFX 代码，以便更多地了解这种语言，我希望有一个带有名为“Iconify”的按钮的窗口，该按钮在单击时会最小化窗口。 Here you can see how it looks like

我正在使用 FXML(场景生成器)，因此我通常不会在类中初始化或声明 Nod(组件)。当我在 start(Stage PrimaryStage) 方法中执行所有操作时，当我使用以下代码时，最小化确实有效:buttonIconify.setOnAction(event -> stage.setIconified(true)); 所以，实际上，当我尝试在 start 中使用 .setIconified(true) 方法时，效果很好。但是，当我尝试从其他方法(如 public void handleButtonAction(ActionEvent event))使用它时，由于某种原因，它并没有使用。

异常(exception):

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1787)
    at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1670)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    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.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:49)
    at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8863)
    at javafx.controls/javafx.scene.control.Button.fire(Button.java:200)
    at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:206)
    at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3876)
    at javafx.graphics/javafx.scene.Scene$MouseHandler.access$1300(Scene.java:3604)
    at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1874)
    at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2613)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:397)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:434)
    at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:433)
    at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
    at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:175)
    at java.base/java.lang.Thread.run(Thread.java:844)
Caused by: java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:76)
    at jdk.internal.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:83)
    at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1782)
    ... 47 more
Caused by: java.lang.NullPointerException
    at app.Main.handleButtonAction(Main.java:39)
    ... 58 more

巨大的...

我不知道为什么它在外部不起作用

@Override
public void start(Stage PrimaryStage) 抛出异常

方法。

我的完整类(class)代码:

package app;

import javafx.application.*;
import javafx.event.*;
import javafx.fxml.*;
import javafx.scene.*;
import javafx.scene.control.*;
import javafx.stage.*;

public class Main extends Application {

    private Stage stage;

    @FXML
    private Button buttonIconify;
    @FXML
    private Button buttonExit;

    @Override
    public void start(Stage primaryStage) throws Exception {
        stage = primaryStage;
        stage.setTitle("JavaFX Test Range");

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

        Scene scene = new Scene(root);
        // scene.getStylesheets().add(getClass().getResource("Stylesheet.css").toExternalForm());
        stage.setScene(scene);
        stage.show();
    }

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

    @FXML
    public void handleButtonAction(ActionEvent event) {
        if (event.getSource() == buttonIconify) {
            stage.setIconified(true);
        }

        if (event.getSource() == buttonExit) {
            Platform.exit();
        }
    }
}

FXML:

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.control.Button?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.layout.HBox?>

<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/9.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="app.Main">
    <HBox alignment="CENTER" prefHeight="400.0" prefWidth="600.0" spacing="30.0" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
        <Button fx:id="buttonIconify" mnemonicParsing="false" onAction="#handleButtonAction" prefHeight="70.0" prefWidth="170.0" text="Iconify" />
        <Button fx:id="buttonExit" mnemonicParsing="false" onAction="#handleButtonAction" prefHeight="70.0" prefWidth="170.0" text="Exit" />
    </HBox>
</AnchorPane>

Answer 1

在 Controller 上调用您的处理程序方法handleButtonAction。您只需在调用 launch() 时创建的 Application 类的实例中初始化字段 stage:它永远不会在 Controller 。因此，当您尝试在 Controller 中调用 stage.setIconified() 时，您会遇到空指针异常。

使用 Application 类作为 Controller 的类始终是一个错误，因为它会导致混淆在哪些实例中初始化哪些字段。

为 Controller 创建一个单独的类，并以通常的方式访问其中的窗口:

@FXML
public void handleButtonAction(ActionEvent event) {
    if (event.getSource() == buttonIconify) {
        Stage stage = (Stage) buttonIconify.getScene().getWindow();
        stage.setIconified(true);
    }

    if (event.getSource() == buttonExit) {
        Platform.exit();
    }
}

就其值(value)而言，我建议对不同的操作使用不同的处理程序，而不是使用一个包含(可能)一大堆 if 语句的大型处理程序。