在borderpane中心加載新的fxml

Question

剛開始使用JavaFx（通常也是Java的初學者），幾天來，我一直在嘗試使其工作，但一直無法解決。 我收到一個空指針異常，該異常在這里介紹： 什么是NullPointerException，如何解決？

所以我希望這個問題不會因為重復而結束，因為我知道npe是什么，並且（通常）知道如何解決此問題。

我也（大多數時候）知道如何躲避它們和/或修復它們（如果發生），但是在這種情況下，我只是不知道如何解決它。

我還檢查了有關fxml的其他問題，但仍然無法解決。
如何從javaFx borderPane中的LeftPane更改CenterPane？
在javaFX的BorderPane中的窗格之間切換
在同一場景中加載新的fxml

在我的應用程序中，我想以borderpane為根，在左側，我有三個按鈕，根據我按的是哪個按鈕，按新的fxml和一個tabpane應該在borderpane的中心加載，當我按下按鈕時，得到一個我認為是由於我沒有參考正確的邊框的npe，但我看不到我要去哪里錯了。

我想做的是當我按下按鈕custMenuButton時，fxml應該加載並設置為borderpane的中心。

主班

import java.io.IOException;
import javafx.application.Application;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;

public class Main extends Application {

    @FXML
    private BorderPane root;

    Stage window;

    @Override
    public void start(Stage primaryStage) throws IOException {
        window = primaryStage;
        FXMLLoader loader = new FXMLLoader(Main.class.getResource("MainWindowView.fxml"));
        this.root = loader.load();

        MainWindowController mwc = new MainWindowController();
        mwc.setMain(this);

        Scene scene = new Scene(root);
        window.setTitle("JavaFX");
        window.setScene(scene);
        window.show();
    }

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

    public BorderPane getBorderPane() {
        return root;
    }     
}

主視窗控制器

import java.io.IOException;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.control.Button;
import javafx.scene.control.TabPane;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.VBox;

public class MainWindowController {

    private Main main;

    @FXML private BorderPane root;
    @FXML private VBox sideBox;
    @FXML private Button custMenuButton;
    @FXML private Button accMenuButton;
    @FXML private Button transMenuButton; 

    public void setMain(Main main) {
        this.main = main;
    }

    public void handleCustMenuButton() throws IOException {        
        FXMLLoader loader = new FXMLLoader(getClass().getResource("CustomerView.fxml"));
        TabPane pane = (TabPane) loader.load();

        CustomerViewController cvc = loader.getController();
        cvc.setMain(main);

        main.getBorderPane().setCenter(pane);
    }
}

客戶視圖控制器

import java.net.URL;
import java.util.ResourceBundle;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Tab;
import javafx.scene.control.TabPane;

public class CustomerViewController implements Initializable {

    Main main;
    @FXML private TabPane custTabPane;
    @FXML private Tab createTab;
    @FXML private Tab listAllTab;
    @FXML private Tab deleteTab;

    public void setMain(Main main){
        this.main = main;
    }

    @Override
    public void initialize(URL url, ResourceBundle rb) {
        // TODO
    }     
}

主窗口視圖

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

<?import javafx.geometry.Insets?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Menu?>
<?import javafx.scene.control.MenuBar?>
<?import javafx.scene.control.MenuItem?>
<?import javafx.scene.layout.BorderPane?>
<?import javafx.scene.layout.VBox?>

<BorderPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="600.0" prefWidth="800.0" xmlns="http://javafx.com/javafx/8.0.141" xmlns:fx="http://javafx.com/fxml/1" fx:controller="firstfx.MainWindowController">
   <top>
      <MenuBar BorderPane.alignment="CENTER">
        <menus>
          <Menu mnemonicParsing="false" text="File">
            <items>
              <MenuItem mnemonicParsing="false" text="Close" />
            </items>
          </Menu>
          <Menu mnemonicParsing="false" text="Help">
            <items>
              <MenuItem mnemonicParsing="false" text="About" />
            </items>
          </Menu>
        </menus>
      </MenuBar>
   </top>
   <left>
      <VBox fx:id="sideBox" prefHeight="200.0" prefWidth="150.0" spacing="2.0" BorderPane.alignment="CENTER">
         <children>
            <Button fx:id="custMenuButton" mnemonicParsing="false" onAction="#handleCustMenuButton" prefHeight="50.0" prefWidth="130.0" text="Kundmeny" />
            <Button fx:id="accMenuButton" mnemonicParsing="false" prefHeight="50.0" prefWidth="130.0" text="Kontomeny" />
            <Button fx:id="transMenuButton" mnemonicParsing="false" prefHeight="50.0" prefWidth="130.0" text="Transaktioner" />
         </children>
         <padding>
            <Insets bottom="10.0" left="10.0" right="10.0" top="10.0" />
         </padding>
      </VBox>
   </left>
</BorderPane>

客戶視圖fxml

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

<?import javafx.scene.control.Tab?>
<?import javafx.scene.control.TabPane?>
<?import javafx.scene.layout.AnchorPane?>

<TabPane fx:id="custTabPane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" tabClosingPolicy="UNAVAILABLE" xmlns="http://javafx.com/javafx/8.0.141" xmlns:fx="http://javafx.com/fxml/1" fx:controller="firstfx.CustomerViewController">
  <tabs>
    <Tab fx:id="createTab" text="Skapa kund">
      <content>
        <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="180.0" prefWidth="200.0" />
      </content>
    </Tab>
    <Tab fx:id="listAllTab" text="Lista alla kunder">
      <content>
        <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="180.0" prefWidth="200.0" />
      </content>
    </Tab>
      <Tab fx:id="deleteTab" text="Radera kund">
        <content>
          <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="180.0" prefWidth="200.0" />
        </content>
      </Tab>
  </tabs>
</TabPane>

堆棧跟蹤

Executing /home/garnbutik/NetBeansProjects/FirstFX/dist/run1223809748/FirstFX.jar using platform /home/garnbutik/jdk1.8.0_151/jre/bin/java
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:8413)
    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$MouseEventNotification.run(GlassViewEventHandler.java:381)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$353(GlassViewEventHandler.java:417)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
    at com.sun.glass.ui.gtk.GtkApplication.lambda$null$48(GtkApplication.java:139)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1771)
    ... 48 more
Caused by: java.lang.NullPointerException
    at firstfx.MainWindowController.handleCustMenuButton(MainWindowController.java:31)
    ... 58 more
BUILD STOPPED (total time: 4 minutes 14 seconds)

Answer 1

您不會在加載MainWindowView.fxml時創建的控制器上調用setMain(...) 。 因此，當您嘗試在MainWindowController中執行此操作時

main.getBorderPane()...

您會得到一個空指針異常。

在start()方法中，您需要以與稍后在handleCustMenuButton(...)相同的方式獲取控制器，即

    FXMLLoader loader = new FXMLLoader(Main.class.getResource("MainWindowView.fxml"));
    this.root = loader.load();

    // MainWindowController mwc = new MainWindowController();

    MainWindowController mwc = loader.getController();
    mwc.setMain(this);