JavaFX 入门 : Modifying Label Text on other window from Main Window

Question

我是一名使用 Scenebuilder 和 MVC 初学者的 javaFx 新人。

我有一个问题如下:我试图创建一个主窗口来提醒新窗口。我尝试中间化警报窗口中的标签文本。但我不能那样做。我收到了这个错误:

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
    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:8411)
    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$MouseHandler.process(Scene.java:3757)
    at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:352)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$355(GlassViewEventHandler.java:388)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:387)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$149(WinApplication.java:191)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1771)
    ... 48 more
Caused by: java.lang.NullPointerException
    at controller.AlertController.setAlertLabel(AlertController.java:36)
    at controller.MainController.onMainButtonClicked(MainController.java:24)
    ... 58 more

我有一个主窗口，其中包含 maincontroller、alertController 和 main.fxml 和alert.fxml，如下所示:

主要:

package app;

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) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("../view/Main.fxml"));
        primaryStage.setTitle("Hello World");
        primaryStage.setScene(new Scene(root));
        primaryStage.show();
    }

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

主 Controller :

package controller;

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

public class MainController {

    AlertController alertController = new AlertController();

    @FXML
    public Label mainLabel;

    @FXML
    public TextField mainTextField;

    @FXML
    public Button mainButton;

    @FXML
    public void onMainButtonClicked() {
        alertController.displayAlert();
        alertController.setAlertLabel("Hello from MainController!");
    }
}

Main.fxml:

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

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

<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8.0.60" xmlns:fx="http://javafx.com/fxml/1" fx:controller="controller.MainController">
   <children>
      <VBox prefHeight="400.0" prefWidth="600.0" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
         <children>
            <HBox alignment="CENTER" prefHeight="154.0" prefWidth="600.0">
               <children>
                  <Label fx:id="mainLabel" alignment="CENTER" contentDisplay="TOP" prefHeight="31.0" prefWidth="115.0" text="Main Text" />
               </children>
            </HBox>
            <HBox alignment="CENTER" centerShape="false" layoutX="10.0" layoutY="10.0">
               <children>
                  <TextField fx:id="mainTextField" alignment="TOP_LEFT" prefHeight="25.0" prefWidth="331.0" />
               </children>
            </HBox>
            <HBox alignment="CENTER" layoutX="10.0" layoutY="10.0" prefHeight="100.0" prefWidth="200.0">
               <children>
                  <Button fx:id="mainButton" mnemonicParsing="false" onAction="#onMainButtonClicked" text="Display Alert &amp;&amp; Set Message Text" />
               </children>
            </HBox>
         </children>
      </VBox>
   </children>
</AnchorPane>

警报 Controller :

package controller;

import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.stage.Stage;

import java.io.IOException;

public class AlertController {
    Stage window;

    @FXML
    public Label alertLabel;

    @FXML
    Button alertButton;

    public void displayAlert() {
        try {
            window = new Stage();
            Parent root = FXMLLoader.load(getClass().getResource("../view/Alert.fxml"));
            Scene scene = new Scene(root);
            window.setScene(scene);
            window.setTitle("Alert");
            window.show();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void setAlertLabel(String str) {
        alertLabel.setText(str);
    }

    @FXML
    public void onAlertButtonClicked() {
        window.close();
    }
}

和Alert.fxml:

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

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

<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="210.0" prefWidth="380.0" xmlns="http://javafx.com/javafx/8.0.60" xmlns:fx="http://javafx.com/fxml/1" fx:controller="controller.AlertController">
   <children>
      <VBox prefHeight="210.0" prefWidth="380.0" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
         <children>
            <HBox alignment="BOTTOM_CENTER" prefHeight="100.0" prefWidth="200.0">
               <children>
                  <Label fx:id="alertLabel" text="Alert Message" />
               </children>
            </HBox>
            <HBox alignment="CENTER" prefHeight="100.0" prefWidth="200.0">
               <children>
                  <Button fx:id="alertButton" mnemonicParsing="false" onAction="#onAlertButtonClicked" text="Close" />
               </children>
            </HBox>
         </children>
      </VBox>
   </children>
</AnchorPane>

请帮我解决这个问题并解释为什么这不起作用。谢谢您的建议。

Answer 1

AlertController 有两个实例:您在 MainController 中使用

创建的实例

AlertController alertController = new AlertController();

以及当您在 displayAlert() 中加载 Alert.fxml 时由 FXMLLoader 创建的一个。

带 @FXML 注释的字段由其创建的实例上的 FXMLLoader 进行初始化。但是，您在 AlertController 实例上调用 setAlertLabel(...)，该实例不是由 FXMLLoader 创建的。 >。所以当你打电话

alertController.setAlertLabel("Hello from MainController!");

属于alertController的alertLabel尚未初始化，出现空指针异常。

简单的解决方案

最简单的修复方法是在 MainController 中加载 Alert.fxml，并检索正确的 Controller 实例:

public class MainController {


    @FXML
    public Label mainLabel;

    @FXML
    public TextField mainTextField;

    @FXML
    public Button mainButton;

    @FXML
    public void onMainButtonClicked() {
        FXMLLoader loader = new FXMLLoader(getClass().getResource("../view/Alert.fxml"));
        Parent root = loader.load();
        AlertController alertController = loader.getController();
        alertController.setAlertLabel("Hello from MainController!");
        Scene scene = new Scene(root);
        window.setScene(scene);
        window.setTitle("Alert");
        window.show();
    }
}

并从 AlertController 中删除 displayAlert() 方法。

<小时/>

自定义组件解决方案

另一种结构上更接近原始版本的替代方案是将 AlertController 替换为 custom component .

Alert.fxml(请注意根元素的更改，并且 fx:controller 已被删除):

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

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

<fx:root type="AnchorPane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="210.0" prefWidth="380.0" xmlns="http://javafx.com/javafx/8.0.60" xmlns:fx="http://javafx.com/fxml/1" >
   <children>
      <VBox prefHeight="210.0" prefWidth="380.0" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
         <children>
            <HBox alignment="BOTTOM_CENTER" prefHeight="100.0" prefWidth="200.0">
               <children>
                  <Label fx:id="alertLabel" text="Alert Message" />
               </children>
            </HBox>
            <HBox alignment="CENTER" prefHeight="100.0" prefWidth="200.0">
               <children>
                  <Button fx:id="alertButton" mnemonicParsing="false" onAction="#onAlertButtonClicked" text="Close" />
               </children>
            </HBox>
         </children>
      </VBox>
   </children>
</fx:root>

AlertController.java:

package controller;

import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.stage.Stage;

import java.io.IOException;

public class AlertController extends AnchorPane {
    Stage window;

    @FXML
    public Label alertLabel;

    @FXML
    Button alertButton;


    public AlertController() {
        window = new Stage();
        try {
            FXMLLoader loader = new FXMLLoader(getClass().getResource("../view/Alert.fxml"));
            loader.setController(this);
            loader.setRoot(this);
            loader.load();
            Scene scene = new Scene(this);
            window.setScene(scene);
            window.setTitle("Alert");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void displayAlert() {
        window.show();
    }

    public void setAlertLabel(String str) {
        alertLabel.setText(str);
    }

    @FXML
    public void onAlertButtonClicked() {
        window.close();
    }
}

现在你的主 Controller 看起来像这样:

package controller;

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

public class MainController {

    AlertController alertController = new AlertController();

    @FXML
    public Label mainLabel;

    @FXML
    public TextField mainTextField;

    @FXML
    public Button mainButton;

    @FXML
    public void onMainButtonClicked() {
        alertController.displayAlert();
        alertController.setAlertLabel("Hello from MainController!");
    }
}