我正在尝试将一个对象从一个 Controller 传递到另一个 Controller 。我传递给 BookViewController 的 rowData 对象对于初始化方法的工作至关重要，如果未设置数据，就会出现 NullPointerException，这确实发生在我的情况下。
初始化方法似乎在 setRowData 方法之前运行。正如我所说，初始化方法依赖于 setRowData 方法的执行。
我在这里错过了什么？
Main.java
public class Main extends Application {
private static Stage primaryStage;
private static BorderPane mainLayout;
@Override
public void start(Stage primaryStage) throws Exception {
Main.primaryStage = primaryStage;
Main.primaryStage.setTitle("BookingApp");
showMainView();
}
private void showMainView() throws IOException {
FXMLLoader loader = new FXMLLoader();
loader.setLocation(Main.class.getResource("MainView.fxml"));
mainLayout = loader.load();
Scene scene = new Scene(mainLayout);
primaryStage.setScene(scene);
primaryStage.show();
}
public static void showBookView(Trip rowData) throws IOException {
FXMLLoader loader = new FXMLLoader();
loader.setLocation(Main.class.getResource("BookView.fxml"));
BorderPane bookTrip = loader.load();
BookViewController bvc = loader.getController();
// The below method never runs.. why?
bvc.setRowData(rowData);
Stage bookStage = new Stage();
bookStage.setTitle("BookingApp");
bookStage.initModality(Modality.WINDOW_MODAL);
bookStage.initOwner(primaryStage);
Scene scene = new Scene(bookTrip);
bookStage.setScene(scene);
bookStage.showAndWait();
}
public static void main(String[] args) {
launch(args);
}
}
BookViewController.java
public class BookViewController implements Initializable {
private String dbUrl = "jdbc:postgresql://localhost:5432/BookingApp";
private String dbUsername = "postgres";
private String dbPassword = "secret";
@FXML
private TextField personnr;
@FXML
private TextField name;
@FXML
private TextField email;
@FXML
private TextField telnr;
@FXML
private Button addTraveler;
@FXML
private Button removeTraveler;
@FXML
private TableView<Traveler> travelers;
@FXML
private TableColumn<?, ?> personnrColumn;
@FXML
private TableColumn<?, ?> nameColumn;
@FXML
private TableColumn<?, ?> emailColumn;
@FXML
private TableColumn<?, ?> telnrColumn;
@FXML
private TableView<Trip> trips;
@FXML
private TableColumn<?, ?> originColumn;
@FXML
private TableColumn<?, ?> destinationColumn;
@FXML
private TableColumn<?, ?> departureColumn;
@FXML
private TableColumn<?, ?> arrivalColumn;
@FXML
private TableColumn<?, ?> driverColumn;
@FXML
private TableColumn<?, ?> priceAmountColumn;
@FXML
private TableColumn<?, ?> seatsColumn;
@FXML
private Button bookTrip;
private Trip rowData;
private ObservableList<Trip> tripData;
public void setRowData(Trip rowData) {
this.rowData = rowData;
// The below println is never printed to the console..
System.out.println("Test");
}
@Override
public void initialize(URL arg0, ResourceBundle arg1) {
addTraveler.setDisable(true);
removeTraveler.setDisable(true);
populateTravelPlan();
}
@FXML
private void populateTravelPlan() {
try {
Connection conn = DriverManager.getConnection(dbUrl, dbUsername, dbPassword);
tripData = FXCollections.observableArrayList();
ResultSet rs = null;
System.out.println(rowData.getTrip1()); // Here it breaks
System.out.println(rowData.getTrip2());
System.out.println(rowData.getTrip3());
if(rowData.getTrip1() != 0 && rowData.getTrip2() == 0 && rowData.getTrip3() == 0) {
rs = conn.createStatement().executeQuery(
"select trip.tripid, connexion.origin, connexion.destination, trip.departure, trip.arrival, trip.driverpnr, trip.priceamount, trip.seats\r\n" +
"from trip, connexion\r\n" +
"where trip.tripid = " + rowData.getTrip1() + "\r\n" +
"and trip.connexionid = connexion.connexionid\r\n" +
"order by departure;");
} else if(rowData.getTrip1() != 0 && rowData.getTrip2() != 0 && rowData.getTrip3() == 0) {
rs = conn.createStatement().executeQuery(
"select trip.tripid, connexion.origin, connexion.destination, trip.departure, trip.arrival, trip.driverpnr, trip.priceamount, trip.seats\r\n" +
"from trip, connexion\r\n" +
"where trip.tripid = " + rowData.getTrip1() + "\r\n" +
"and trip.connexionid = connexion.connexionid\r\n" +
"union\r\n" +
"select trip.tripid, connexion.origin, connexion.destination, trip.departure, trip.arrival, trip.driverpnr, trip.priceamount, trip.seats\r\n" +
"from trip, connexion\r\n" +
"where trip.tripid = " + rowData.getTrip2() + "\r\n" +
"and trip.connexionid = connexion.connexionid\r\n" +
"order by departure;");
} else if(rowData.getTrip1() != 0 && rowData.getTrip2() != 0 && rowData.getTrip3() != 0) {
rs = conn.createStatement().executeQuery(
"select trip.tripid, connexion.origin, connexion.destination, trip.departure, trip.arrival, trip.driverpnr, trip.priceamount, trip.seats\r\n" +
"from trip, connexion\r\n" +
"where trip.tripid = " + rowData.getTrip1() + "\r\n" +
"and trip.connexionid = connexion.connexionid\r\n" +
"union\r\n" +
"select trip.tripid, connexion.origin, connexion.destination, trip.departure, trip.arrival, trip.driverpnr, trip.priceamount, trip.seats\r\n" +
"from trip, connexion\r\n" +
"where trip.tripid = " + rowData.getTrip2() + "\r\n" +
"and trip.connexionid = connexion.connexionid\r\n" +
"union\r\n" +
"select trip.tripid, connexion.origin, connexion.destination, trip.departure, trip.arrival, trip.driverpnr, trip.priceamount, trip.seats\r\n" +
"from trip, connexion\r\n" +
"where trip.tripid = " + rowData.getTrip3() + "\r\n" +
"and trip.connexionid = connexion.connexionid\r\n" +
"order by departure;");
}
tripData.add(new Trip(rs.getInt(1), rs.getString(2), rs.getString(3), ""+rs.getTimestamp(4), ""+rs.getTimestamp(5), rs.getString(6), ""+rs.getInt(7), ""+rs.getInt(8)));
while(rs.next()) {
tripData.add(new Trip(rs.getInt(1), rs.getString(2), rs.getString(3), ""+rs.getTimestamp(4), ""+rs.getTimestamp(5), rs.getString(6), ""+rs.getInt(7), ""+rs.getInt(8)));
}
} catch (SQLException e) {
e.printStackTrace();
}
trips.setItems(tripData);
}
}
异常
javafx.fxml.LoadException:
/C:/Users/David/Desktop/eclipse/BookingApp1/bin/booking/BookView.fxml
at javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2601)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2579)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2441)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2409)
at booking.Main.showBookView(Main.java:35)
at booking.MainViewController$1.handle(MainViewController.java:227)
at booking.MainViewController$1.handle(MainViewController.java:1)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Scene$ClickGenerator.postProcess(Scene.java:3470)
at javafx.scene.Scene$ClickGenerator.access$8100(Scene.java:3398)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3766)
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$353(GlassViewEventHandler.java:417)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$147(WinApplication.java:177)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
at booking.BookViewController.populateTravelPlan(BookViewController.java:109)
at booking.BookViewController.initialize(BookViewController.java:100)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
... 39 more
最佳答案
It seems that the initialize-method runs BEFORE the setRowData-method.
这确实是正确的。 initialize() 方法由 FXMLLoader 调用，作为执行 load() 的一部分，这必然发生在您有机会之前调用setRowData(...)。
What am I missing out on here?
没什么，真的。
有几个可能的修复方法。一种是简单地避免 initialize() 方法依赖于传递给 setRowData() 的数据，并将依赖于这些数据的任何代码移至后一个方法。在这种情况下这是非常微不足道的:
public void setRowData(Trip rowData) {
this.rowData = rowData;
populateTravelPlan();
}
@Override
public void initialize(URL arg0, ResourceBundle arg1) {
addTraveler.setDisable(true);
removeTraveler.setDisable(true);
// don't do this here:
// populateTravelPlan();
}
如果您不喜欢该解决方案，另一种选择是在代码中而不是在 FXML 中设置 Controller 。简而言之，您可以从 FXML 文件中删除 fx:controller 属性，然后在加载 FXML 时创建一个 Controller 实例，调用 setRowData() (或以其他方式初始化行数据，例如通过构造函数)，并在 FXMLLoader 上调用 setController()。此解决方案在Passing Parameters JavaFX FXML中有详细描述。 .
该解决方案的一个缺点是，如果您使用场景生成器进行 FXML 设计，场景生成器将失去一些功能(因为它不再知道用于创建 Controller 的类)。如果您想保留该功能，可以使用 Controller 工厂。
对于该解决方案，我将修改 Controller ，以便将行数据传递给构造函数:
public class BookViewController implements Initializable {
// @FXML-annotated fields omitted...
private final Trip rowData;
public BookViewController(Trip rowData) {
this.rowData = rowData ;
}
// remove this, it is now initialized in the constructor
// public void setRowData(Trip rowData) {
// this.rowData = rowData;
// // The below println is never printed to the console..
// System.out.println("Test");
// }
@Override
public void initialize(URL arg0, ResourceBundle arg1) {
addTraveler.setDisable(true);
removeTraveler.setDisable(true);
populateTravelPlan();
}
// etc...
}
此构造函数将阻止 FXMLLoader 使用其默认方法创建 Controller 实例，因此请向加载器提供 Controller 工厂以覆盖 Controller 的创建方式:
public static void showBookView(Trip rowData) throws IOException {
FXMLLoader loader = new FXMLLoader();
loader.setLocation(Main.class.getResource("BookView.fxml"));
loader.setControllerFactory(type -> {
if (type == BookViewController.class) {
return new BookViewController(rowData);
}
// default behavior: need this in case there are <fx:include> in the FXML
try {
return type.getConstructor().newInstance();
} catch (Exception exc) {
// fatal...
throw new RuntimeException(exc);
}
});
BorderPane bookTrip = loader.load();
Stage bookStage = new Stage();
bookStage.setTitle("BookingApp");
bookStage.initModality(Modality.WINDOW_MODAL);
bookStage.initOwner(primaryStage);
Scene scene = new Scene(bookTrip);
bookStage.setScene(scene);
bookStage.showAndWait();
}
关于java - 初始化方法在主类中的指定方法之前运行，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/49651919/