複数のアクションを複数回実行できない

Question

複数回何かをしようとするたびにプログラムがクラッシュするという問題が発生しています。たとえば、私がログインしてからログアウトしてもう一度ログインし直すと、プログラムがクラッシュします。これは、他のシーンに切り替えたり、家に帰ったり、もう一度別のシーンに戻ったりしようとするなど、何度もやりたいことのために起こっています。

ログイン部分のコードを投稿するだけです。

メイン

package libraryapp; 

import java.io.File; 
import java.io.IOException; 
import java.util.prefs.Preferences; 

import javafx.application.Application; 
import javafx.collections.FXCollections; 
import javafx.collections.ObservableList; 
import javafx.fxml.FXMLLoader; 
import javafx.scene.Scene; 
import javafx.scene.control.Alert; 
import javafx.scene.control.Alert.AlertType; 
import javafx.scene.layout.AnchorPane; 
import javafx.scene.layout.BorderPane; 
import javafx.stage.Stage; 
import javax.xml.bind.JAXBContext; 
import javax.xml.bind.Marshaller; 
import javax.xml.bind.Unmarshaller; 
import libraryapp.model.Book; 
import libraryapp.model.BookListWrapper; 
import libraryapp.view.BrowseController; 
import libraryapp.view.HomeOverviewController; 
import libraryapp.view.LoginController; 
import libraryapp.view.RootLayoutController; 

public class LibraryApp extends Application { 

private Stage primaryStage; 
private BorderPane rootLayout; 
/** 
* The data as an observable list of Books. 
*/ 
private ObservableList<Book> bookData = FXCollections.observableArrayList(); 

/** 
* Constructor 
*/ 
public LibraryApp() { 
    // Add some sample data 
    bookData.add(new Book("Hans", "Muster")); 
    bookData.add(new Book("Ruth", "Mueller")); 
    bookData.add(new Book("Heinz", "Kurz")); 
    bookData.add(new Book("Cornelia", "Meier")); 
    bookData.add(new Book("Werner", "Meyer")); 
    bookData.add(new Book("Lydia", "Kunz")); 
    bookData.add(new Book("Anna", "Best")); 
    bookData.add(new Book("Stefan", "Meier")); 
    bookData.add(new Book("Martin", "Mueller")); 
} 

/** 
* Returns the data as an observable list of Books. 
* @return 
*/ 
public ObservableList<Book> getBookData() { 
    return bookData; 
} 




@Override 
public void start(Stage primaryStage) { 
    this.primaryStage = primaryStage; 
    this.primaryStage.setTitle("LibraryApp"); 
    initRootLayout(); 
    showLogin(); 
} 


/** 
* Initializes the root layout and tries to load the last opened 
* person file. 
*/ 
public void initRootLayout() { 
try { 
    // Load root layout from fxml file. 
    FXMLLoader loader = new FXMLLoader(); 
     loader.setLocation(LibraryApp.class.getResource("view/RootLayout.fxml")); 
    rootLayout = (BorderPane) loader.load(); 

    // Show the scene containing the root layout. 
    Scene scene = new Scene(rootLayout); 
    primaryStage.setScene(scene); 

    // Give the controller access to the main app. 
    RootLayoutController controller = loader.getController(); 
    controller.setLibraryApp(this); 

    primaryStage.show(); 
} catch (IOException e) { 
    e.printStackTrace(); 
} 

// Try to load last opened person file. 
File file = getBookFilePath(); 
if (file != null) { 
    loadBookDataFromFile(file); 
} 
} 





/** 
* Shows the home overview inside the root layout. 
*/ 
public void showHomeOverview() { 
    try { 

     FXMLLoader loader = new FXMLLoader(); 
     loader.setLocation(LibraryApp.class.getResource("view/HomeOverview.fxml")); 
     AnchorPane homeOverview = (AnchorPane) loader.load(); 



     // Set home overview into the center of root layout. 
     rootLayout.setCenter(homeOverview); 

    // Give the controller access to the main app. 
    HomeOverviewController controller = loader.getController(); 
    controller.setLibraryApp(this); 


    } catch (IOException e) { 
     e.printStackTrace(); 
    } 
} 

public void showLogin() { 
    try { 

     FXMLLoader loader = new FXMLLoader(); 
     loader.setLocation(LibraryApp.class.getResource("view/Login.fxml")); 
     AnchorPane login = (AnchorPane) loader.load(); 



     // Set home overview into the center of root layout. 
     rootLayout.setCenter(login); 

    // Give the controller access to the main app. 
    LoginController controller = loader.getController(); 
    controller.setLibraryApp(this); 


    } catch (IOException e) { 
     e.printStackTrace(); 
    } 
} 

public void showBrowse() { 
try { 

    FXMLLoader loader = new FXMLLoader(); 
    loader.setLocation(LibraryApp.class.getResource("view/Browse.fxml")); 
    AnchorPane browse = (AnchorPane) loader.load(); 

    // Set browse into the center of root layout. 
    rootLayout.setCenter(browse); 

    // Give the controller access to the main app. 
    BrowseController controller = loader.getController(); 
    controller.setLibraryApp(this); 

} catch (IOException e) { 
    e.printStackTrace(); 
} 
} 


/** 
* Returns the main stage. 
* @return 
*/ 
public Stage getPrimaryStage() { 
    return primaryStage; 
} 

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

ログインコントローラ

package libraryapp.view; 

import java.io.File; 
import java.io.IOException; 
import java.net.URL; 
import java.util.ResourceBundle; 
import javafx.event.ActionEvent; 
import javafx.fxml.FXML; 
import javafx.fxml.FXMLLoader; 
import javafx.fxml.Initializable; 
import javafx.scene.control.Label; 
import javafx.scene.control.PasswordField; 
import javafx.scene.control.TextField; 
import javafx.scene.layout.AnchorPane; 
import javax.xml.parsers.DocumentBuilder; 
import javax.xml.parsers.DocumentBuilderFactory; 
import javax.xml.parsers.ParserConfigurationException; 
import libraryapp.LibraryApp; 
import org.w3c.dom.Document; 
import org.w3c.dom.NodeList; 
import org.xml.sax.SAXException; 

/** 
* FXML Controller class 
* 
* @author Michael 
*/ 
public class LoginController implements Initializable { 

/** 
* Initializes the controller class. 
*/ 

    @FXML 
private AnchorPane loginPane; 



@FXML 
private Label lblMessage; 
@FXML 
private TextField txtUsername; 
@FXML 
private PasswordField txtPassword; 

private LibraryApp libraryApp; 


public String getString(String tagName) throws SAXException, IOException,  ParserConfigurationException{ 
    File file = new File("src/libraryapp/account.xml"); 
    DocumentBuilderFactory docBuildFactory = DocumentBuilderFactory.newInstance(); 
    DocumentBuilder docBuilder = docBuildFactory.newDocumentBuilder(); 
    Document document = docBuilder.parse(file); 

    NodeList list = document.getElementsByTagName(tagName); 
    if (list != null && list.getLength() > 0){ 
     NodeList subList = list.item(0).getChildNodes(); 

     if (subList != null && subList.getLength() > 0) { 
      return subList.item(0).getNodeValue(); 
     } 
    } 
     return null; 
    } 

@FXML 
private void login(ActionEvent event) throws IOException, ParserConfigurationException, SAXException { 


    String email = getString("email"); 

    String password = getString("password"); 


    if (txtUsername.getText().equals(email) && txtPassword.getText().equals(password)){ 

     libraryApp.showHomeOverview(); 
    } else{ 
     lblMessage.setText("Username or password invalid!"); 
    } 


} 

    @FXML 
private void register(ActionEvent event) throws IOException { 

    AnchorPane pane = FXMLLoader.load(getClass().getResource("Register.fxml")); 
    loginPane.getChildren().setAll(pane); 
} 

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

public void setLibraryApp(LibraryApp libraryApp) { 
    this.libraryApp = libraryApp; 
} 

} 

そして、これは私が手にエラーがある

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.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.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$354(GlassViewEventHandler.java:417) 
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389) 
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416) 
at com.sun.glass.ui.View.handleMouseEvent(View.java:555) 
at com.sun.glass.ui.View.notifyMouse(View.java:937) 
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method) 
at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191) 
at java.lang.Thread.run(Thread.java:745) 
Caused by: java.lang.reflect.InvocationTargetException 
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) 
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) 
at java.lang.reflect.Method.invoke(Method.java:498) 
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71) 
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source) 
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) 
at java.lang.reflect.Method.invoke(Method.java:498) 
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275) 
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769) 
... 52 more 
Caused by: java.lang.NullPointerException 
at libraryapp.view.LoginController.login(LoginController.java:82) 
... 62 more 

ログアウト

@FXML 
public void logout(ActionEvent event) throws IOException { 

     File bookFile = libraryApp.getBookFilePath(); 
     libraryApp.saveBookDataToFile(bookFile); 


    AnchorPane pane = FXMLLoader.load(getClass().getResource("Login.fxml")); 
    browsePane.getChildren().setAll(pane); 
} 

Answer 1

logout()の実装では、再びログインFXMLファイルをロードしますが、新しいコントローラにlibraryAppフィールドを設定しません。したがって、コントローラのそのインスタンスではそのフィールドはnullであり、NULLポインタ例外が発生します。

すでにlibraryAppへの参照を持っているので、あなたがNULLである変数

libraryApp.showLogin();