尝试在根布局中的窗格之间切换时出现 NullPointer
NullPointer when trying to switch between panes in rootlayout
我有一个程序，其中我有一个 BorderPane 作为根布局，并且想在根布局内的 Anchorpane 之间切换。当我 运行 应用程序时，带有锚定面板 "login" 的根布局显示得很好。但是，当我尝试将根布局中的锚窗格切换为 "startMenu" 时，即使我使用与 "Login" 相同的方法，我也会得到 NullPointerException。请帮忙！ :)
在我的 main class 中，我想要的越少越好，所以我只有 main 和 start 方法来启动应用程序并显示登录屏幕：
package controller;
import javafx.application.Application;
import javafx.stage.Stage;
public class Main extends Application {
Controller controller = new Controller();
private Stage window;
public static void main(String[] args) {
launch(args);
}
public void start(Stage primaryStage) {
this.window = primaryStage;
this.window.setTitle("Title");
controller.setWindow(window);
controller.initRootLayout();
controller.showLogin();
}
}
控制器class:
package controller;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;
import javafx.scene.control.Button;
import java.io.IOException;
public class Controller{
private BorderPane rootLayout;
public Stage window;
public Button btnOk;
public FXMLLoader loader = new FXMLLoader();
public void initRootLayout() {
try {
// Load root layout from fxml file.
FXMLLoader loader = new FXMLLoader();
loader.setLocation(Controller.class.getResource("/gui/rootLayout.fxml"));
rootLayout = loader.load();
// Show the scene containing the root layout.
Scene scene = new Scene(rootLayout);
window.setScene(scene);
window.show();
} catch (IOException e) {
e.printStackTrace();
}
}
public void showLogin() {
try {
// Load login.fxml.
FXMLLoader loader = new FXMLLoader();
loader.setLocation(Controller.class.getResource("/gui/login.fxml"));
AnchorPane login = loader.load();
// Set login.fxml into the center of root layout.
rootLayout.setCenter(login);
} catch (IOException e) {
e.printStackTrace();
}
}
public void showStartMenu(){
try {
FXMLLoader loader = new FXMLLoader();
loader.setLocation(Controller.class.getResource("/gui/startMenu.fxml"));
AnchorPane startMenu = loader.load();
rootLayout.setCenter(startMenu);
} catch (IOException e) {
e.printStackTrace();
}
}
public void handleLogin(){
showStartMenu();
}
public void setWindow(Stage window) {
this.window = window;
}
}
我的登录 FXML 文件：
<?import javafx.scene.effect.*?>
<?import javafx.scene.text.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="600.0" prefWidth="800.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="controller.Controller">
<children>
<Label layoutX="353.0" layoutY="150.0" text="Sign in" textAlignment="CENTER">
<font>
<Font size="34.0" />
</font>
</Label>
<TextField fx:id="fieldUsername" layoutX="311.0" layoutY="239.0" />
<PasswordField fx:id="fieldPassword" layoutX="311.0" layoutY="312.0" />
<Button fx:id="btnOk" layoutX="467.0" layoutY="436.0" mnemonicParsing="false" onAction="#handleLogin" prefHeight="31.0" prefWidth="73.0" text="OK" />
<Hyperlink fx:id="linkForgotPassword" layoutX="375.0" layoutY="343.0" text="Forgot password?" textOverrun="CLIP" underline="true">
<effect>
<Blend />
</effect></Hyperlink>
</children>
</AnchorPane>
最后是我的堆栈跟踪：
"C:\Program Files\Java\jdk1.8.0_20\bin\java" -Didea.launcher.port=7545 "-Didea.launcher.bin.path=C:\Program Files (x86)\JetBrains\IntelliJ IDEA 14.1.4\bin" -Dfile.encoding=windows-1252 -classpath "C:\Program Files\Java\jdk1.8.0_20\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\rt.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\zipfs.jar;C:\Users\Mikkel\Documents\Client\out\production\JavaFxApplication;C:\Program Files (x86)\JetBrains\IntelliJ IDEA 14.1.4\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMain controller.Main
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.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase.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$MouseHandler.access00(Scene.java:3452)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1728)
at javafx.scene.Scene$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)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null1(WinApplication.java:102)
at com.sun.glass.ui.win.WinApplication$$Lambda/1399457240.run(Unknown Source)
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: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)
... 47 more
Caused by: java.lang.NullPointerException
at controller.Controller.showStartMenu(Controller.java:55)
at controller.Controller.handleLogin(Controller.java:63)
... 57 more
您有多个 Controller 实例：一个是您在 Main 中使用 Controller controller = new Controller() 创建的，另一个是由 FXMLLoader 创建的，因为您指定 fx:controller="controller.Controller"。
您初始化 rootLayout 的唯一地方是在 initRootLayout 方法中，并且该方法 仅 在您在 [=19] 中创建的实例上调用=].
因此，对于 FXMLLoader 创建的实例，rootLayout 永远不会被初始化。这意味着当您按下按钮，并且在 FXMLLoader 创建的控制器实例上调用 handleLogin() 时，当您执行 rootLayout.setCenter(..).[=34 时，您会得到一个 NullPointerException =]
下面是我将如何构建这样的内容。如果要将 FXML 的加载委托给控制器，可以使用 How to understand and use `<fx:root>` , in JavaFX? 中概述的 <fx:root> 结构。所以：
application/Main.java:
package application;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.stage.Stage;
import ui.root.RootPane;
public class Main extends Application {
@Override
public void start(Stage primaryStage) throws Exception {
primaryStage.setScene(new Scene(new RootPane(), 600, 600));
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}
ui/root/RootPane.java:
package ui.root;
import java.io.IOException;
import javafx.fxml.FXMLLoader;
import javafx.scene.layout.BorderPane;
import model.Model;
import ui.login.LoginController;
import ui.menu.MenuController;
public class RootPane extends BorderPane {
private final Model model ;
public RootPane() throws Exception {
model = new Model();
model.loggedInProperty().addListener((obs, wasLoggedIn, isLoggedIn) -> {
if (isLoggedIn) {
showMenu();
} else {
showLogin();
}
});
FXMLLoader loader = new FXMLLoader(getClass().getResource("root.fxml"));
loader.setController(this);
loader.setRoot(this);
loader.load();
showLogin();
}
private void showMenu() {
try {
FXMLLoader loader = new FXMLLoader(getClass().getResource("/ui/menu/menu.fxml"));
setCenter(loader.load());
MenuController controller = loader.getController();
controller.setModel(model);
} catch (IOException e) {
e.printStackTrace();
}
}
private void showLogin() {
try {
FXMLLoader loader = new FXMLLoader(getClass().getResource("/ui/login/login.fxml"));
setCenter(loader.load());
LoginController controller = loader.getController();
controller.setModel(model);
} catch (IOException e) {
e.printStackTrace();
}
}
}
model/Model.java（本质上是一个视图模型，跟踪用户是否登录）：
package model;
import javafx.beans.property.BooleanProperty;
import javafx.beans.property.SimpleBooleanProperty;
public class Model {
private BooleanProperty loggedIn = new SimpleBooleanProperty();
public final BooleanProperty loggedInProperty() {
return this.loggedIn;
}
public final boolean isLoggedIn() {
return this.loggedInProperty().get();
}
public final void setLoggedIn(final boolean loggedIn) {
this.loggedInProperty().set(loggedIn);
}
}
root/root.fxml:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.layout.BorderPane?>
<?import javafx.scene.control.Label?>
<fx:root xmlns:fx="http://javafx.com/fxml/1" type="BorderPane">
<top>
<Label text="Login Screen Example" style="-fx-font-size: 16pt; -fx-font-family:sans-serif;"/>
</top>
</fx:root>
ui/login/login.fxml:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.layout.ColumnConstraints?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.control.PasswordField?>
<?import javafx.scene.control.Button?>
<GridPane xmlns:fx="http://javafx.com/fxml/1" fx:controller="ui.login.LoginController">
<columnConstraints>
<ColumnConstraints halignment="RIGHT" hgrow="NEVER"/>
<ColumnConstraints halignment="LEFT" hgrow="SOMETIMES" />
</columnConstraints>
<Label text="Username:" GridPane.columnIndex="0" GridPane.rowIndex="0"/>
<Label text="Password:" GridPane.columnIndex="0" GridPane.rowIndex="1"/>
<TextField fx:id="userField" GridPane.columnIndex="1" GridPane.rowIndex="0"/>
<PasswordField fx:id="passwordField" GridPane.columnIndex="1" GridPane.rowIndex="1"/>
<Button text="Login" onAction="#login" GridPane.rowIndex="2" GridPane.columnSpan="2" GridPane.halignment="CENTER"/>
</GridPane>
ui/login/LoginController.java:
package ui.login;
import javafx.fxml.FXML;
import javafx.scene.control.PasswordField;
import javafx.scene.control.TextField;
import model.Model;
public class LoginController {
private Model model ;
public Model getModel() {
return model;
}
public void setModel(Model model) {
this.model = model;
}
@FXML
private TextField userField ;
@FXML
private PasswordField passwordField ;
@FXML
private void login() {
String user = userField.getText() ;
String password = passwordField.getText();
// verify...
model.setLoggedIn(true);
}
}
ui/menu/menu.fxml:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.layout.HBox?>
<?import javafx.scene.control.Button?>
<HBox xmlns:fx="http://javafx.com/fxml/1" alignment="CENTER" fx:controller="ui.menu.MenuController">
<Button text="Some Action" onAction="#someAction"/>
<Button text="Logout" onAction="#logout"/>
<Button text="Exit" onAction="#exit" fx:id="exitButton"/>
</HBox>
ui/menu/MenuController.java:
package ui.menu;
import javafx.fxml.FXML;
import javafx.scene.control.Button;
import model.Model;
public class MenuController {
private Model model ;
@FXML
private Button exitButton ;
public Model getModel() {
return model;
}
public void setModel(Model model) {
this.model = model;
}
@FXML
private void logout() {
model.setLoggedIn(false);
}
@FXML
private void someAction() {
System.out.println("Some action....");
}
@FXML
private void exit() {
exitButton.getScene().getWindow().hide();
}
}
我有一个程序，其中我有一个 BorderPane 作为根布局，并且想在根布局内的 Anchorpane 之间切换。当我 运行 应用程序时，带有锚定面板 "login" 的根布局显示得很好。但是，当我尝试将根布局中的锚窗格切换为 "startMenu" 时，即使我使用与 "Login" 相同的方法，我也会得到 NullPointerException。请帮忙！ :)
在我的 main class 中，我想要的越少越好，所以我只有 main 和 start 方法来启动应用程序并显示登录屏幕：
package controller;
import javafx.application.Application;
import javafx.stage.Stage;
public class Main extends Application {
Controller controller = new Controller();
private Stage window;
public static void main(String[] args) {
launch(args);
}
public void start(Stage primaryStage) {
this.window = primaryStage;
this.window.setTitle("Title");
controller.setWindow(window);
controller.initRootLayout();
controller.showLogin();
}
}
控制器class:
package controller;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;
import javafx.scene.control.Button;
import java.io.IOException;
public class Controller{
private BorderPane rootLayout;
public Stage window;
public Button btnOk;
public FXMLLoader loader = new FXMLLoader();
public void initRootLayout() {
try {
// Load root layout from fxml file.
FXMLLoader loader = new FXMLLoader();
loader.setLocation(Controller.class.getResource("/gui/rootLayout.fxml"));
rootLayout = loader.load();
// Show the scene containing the root layout.
Scene scene = new Scene(rootLayout);
window.setScene(scene);
window.show();
} catch (IOException e) {
e.printStackTrace();
}
}
public void showLogin() {
try {
// Load login.fxml.
FXMLLoader loader = new FXMLLoader();
loader.setLocation(Controller.class.getResource("/gui/login.fxml"));
AnchorPane login = loader.load();
// Set login.fxml into the center of root layout.
rootLayout.setCenter(login);
} catch (IOException e) {
e.printStackTrace();
}
}
public void showStartMenu(){
try {
FXMLLoader loader = new FXMLLoader();
loader.setLocation(Controller.class.getResource("/gui/startMenu.fxml"));
AnchorPane startMenu = loader.load();
rootLayout.setCenter(startMenu);
} catch (IOException e) {
e.printStackTrace();
}
}
public void handleLogin(){
showStartMenu();
}
public void setWindow(Stage window) {
this.window = window;
}
}
我的登录 FXML 文件：
<?import javafx.scene.effect.*?>
<?import javafx.scene.text.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="600.0" prefWidth="800.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="controller.Controller">
<children>
<Label layoutX="353.0" layoutY="150.0" text="Sign in" textAlignment="CENTER">
<font>
<Font size="34.0" />
</font>
</Label>
<TextField fx:id="fieldUsername" layoutX="311.0" layoutY="239.0" />
<PasswordField fx:id="fieldPassword" layoutX="311.0" layoutY="312.0" />
<Button fx:id="btnOk" layoutX="467.0" layoutY="436.0" mnemonicParsing="false" onAction="#handleLogin" prefHeight="31.0" prefWidth="73.0" text="OK" />
<Hyperlink fx:id="linkForgotPassword" layoutX="375.0" layoutY="343.0" text="Forgot password?" textOverrun="CLIP" underline="true">
<effect>
<Blend />
</effect></Hyperlink>
</children>
</AnchorPane>
最后是我的堆栈跟踪：
"C:\Program Files\Java\jdk1.8.0_20\bin\java" -Didea.launcher.port=7545 "-Didea.launcher.bin.path=C:\Program Files (x86)\JetBrains\IntelliJ IDEA 14.1.4\bin" -Dfile.encoding=windows-1252 -classpath "C:\Program Files\Java\jdk1.8.0_20\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\rt.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_20\jre\lib\ext\zipfs.jar;C:\Users\Mikkel\Documents\Client\out\production\JavaFxApplication;C:\Program Files (x86)\JetBrains\IntelliJ IDEA 14.1.4\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMain controller.Main
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.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase.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.access00(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)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null1(WinApplication.java:102)
at com.sun.glass.ui.win.WinApplication$$Lambda/1399457240.run(Unknown Source)
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: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)
... 47 more
Caused by: java.lang.NullPointerException
at controller.Controller.showStartMenu(Controller.java:55)
at controller.Controller.handleLogin(Controller.java:63)
... 57 more
您有多个 Controller 实例：一个是您在 Main 中使用 Controller controller = new Controller() 创建的，另一个是由 FXMLLoader 创建的，因为您指定 fx:controller="controller.Controller"。
您初始化 rootLayout 的唯一地方是在 initRootLayout 方法中，并且该方法 仅 在您在 [=19] 中创建的实例上调用=].
因此，对于 FXMLLoader 创建的实例，rootLayout 永远不会被初始化。这意味着当您按下按钮，并且在 FXMLLoader 创建的控制器实例上调用 handleLogin() 时，当您执行 rootLayout.setCenter(..).[=34 时，您会得到一个 NullPointerException =]
下面是我将如何构建这样的内容。如果要将 FXML 的加载委托给控制器，可以使用 How to understand and use `<fx:root>` , in JavaFX? 中概述的 <fx:root> 结构。所以：
application/Main.java:
package application;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.stage.Stage;
import ui.root.RootPane;
public class Main extends Application {
@Override
public void start(Stage primaryStage) throws Exception {
primaryStage.setScene(new Scene(new RootPane(), 600, 600));
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}
ui/root/RootPane.java:
package ui.root;
import java.io.IOException;
import javafx.fxml.FXMLLoader;
import javafx.scene.layout.BorderPane;
import model.Model;
import ui.login.LoginController;
import ui.menu.MenuController;
public class RootPane extends BorderPane {
private final Model model ;
public RootPane() throws Exception {
model = new Model();
model.loggedInProperty().addListener((obs, wasLoggedIn, isLoggedIn) -> {
if (isLoggedIn) {
showMenu();
} else {
showLogin();
}
});
FXMLLoader loader = new FXMLLoader(getClass().getResource("root.fxml"));
loader.setController(this);
loader.setRoot(this);
loader.load();
showLogin();
}
private void showMenu() {
try {
FXMLLoader loader = new FXMLLoader(getClass().getResource("/ui/menu/menu.fxml"));
setCenter(loader.load());
MenuController controller = loader.getController();
controller.setModel(model);
} catch (IOException e) {
e.printStackTrace();
}
}
private void showLogin() {
try {
FXMLLoader loader = new FXMLLoader(getClass().getResource("/ui/login/login.fxml"));
setCenter(loader.load());
LoginController controller = loader.getController();
controller.setModel(model);
} catch (IOException e) {
e.printStackTrace();
}
}
}
model/Model.java（本质上是一个视图模型，跟踪用户是否登录）：
package model;
import javafx.beans.property.BooleanProperty;
import javafx.beans.property.SimpleBooleanProperty;
public class Model {
private BooleanProperty loggedIn = new SimpleBooleanProperty();
public final BooleanProperty loggedInProperty() {
return this.loggedIn;
}
public final boolean isLoggedIn() {
return this.loggedInProperty().get();
}
public final void setLoggedIn(final boolean loggedIn) {
this.loggedInProperty().set(loggedIn);
}
}
root/root.fxml:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.layout.BorderPane?>
<?import javafx.scene.control.Label?>
<fx:root xmlns:fx="http://javafx.com/fxml/1" type="BorderPane">
<top>
<Label text="Login Screen Example" style="-fx-font-size: 16pt; -fx-font-family:sans-serif;"/>
</top>
</fx:root>
ui/login/login.fxml:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.layout.ColumnConstraints?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.control.PasswordField?>
<?import javafx.scene.control.Button?>
<GridPane xmlns:fx="http://javafx.com/fxml/1" fx:controller="ui.login.LoginController">
<columnConstraints>
<ColumnConstraints halignment="RIGHT" hgrow="NEVER"/>
<ColumnConstraints halignment="LEFT" hgrow="SOMETIMES" />
</columnConstraints>
<Label text="Username:" GridPane.columnIndex="0" GridPane.rowIndex="0"/>
<Label text="Password:" GridPane.columnIndex="0" GridPane.rowIndex="1"/>
<TextField fx:id="userField" GridPane.columnIndex="1" GridPane.rowIndex="0"/>
<PasswordField fx:id="passwordField" GridPane.columnIndex="1" GridPane.rowIndex="1"/>
<Button text="Login" onAction="#login" GridPane.rowIndex="2" GridPane.columnSpan="2" GridPane.halignment="CENTER"/>
</GridPane>
ui/login/LoginController.java:
package ui.login;
import javafx.fxml.FXML;
import javafx.scene.control.PasswordField;
import javafx.scene.control.TextField;
import model.Model;
public class LoginController {
private Model model ;
public Model getModel() {
return model;
}
public void setModel(Model model) {
this.model = model;
}
@FXML
private TextField userField ;
@FXML
private PasswordField passwordField ;
@FXML
private void login() {
String user = userField.getText() ;
String password = passwordField.getText();
// verify...
model.setLoggedIn(true);
}
}
ui/menu/menu.fxml:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.layout.HBox?>
<?import javafx.scene.control.Button?>
<HBox xmlns:fx="http://javafx.com/fxml/1" alignment="CENTER" fx:controller="ui.menu.MenuController">
<Button text="Some Action" onAction="#someAction"/>
<Button text="Logout" onAction="#logout"/>
<Button text="Exit" onAction="#exit" fx:id="exitButton"/>
</HBox>
ui/menu/MenuController.java:
package ui.menu;
import javafx.fxml.FXML;
import javafx.scene.control.Button;
import model.Model;
public class MenuController {
private Model model ;
@FXML
private Button exitButton ;
public Model getModel() {
return model;
}
public void setModel(Model model) {
this.model = model;
}
@FXML
private void logout() {
model.setLoggedIn(false);
}
@FXML
private void someAction() {
System.out.println("Some action....");
}
@FXML
private void exit() {
exitButton.getScene().getWindow().hide();
}
}