使用场景生成器8.0在JavaFX中使用setCenter()方法获取空指针异常
我创建了一个小程序来重现我在实际项目中遇到的错误。我有一个名为使用场景生成器8.0在JavaFX中使用setCenter()方法获取空指针异常,java,eclipse,javafx,nullpointerexception,scenebuilder,Java,Eclipse,Javafx,Nullpointerexception,Scenebuilder,我创建了一个小程序来重现我在实际项目中遇到的错误。我有一个名为MainWindow.java的控制器类,它负责两个.fxml文件:MainWindow.fxml和AnchorTest.fxml 控制器类的代码: package projecterror.controller; import java.io.IOException; import javafx.application.Application; import javafx.fxml.FXML; import javafx.fxm
MainWindow.java
的控制器类,它负责两个.fxml文件:MainWindow.fxml
和AnchorTest.fxml
控制器类的代码:
package projecterror.controller;
import java.io.IOException;
import javafx.application.Application;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.geometry.Rectangle2D;
import javafx.scene.Scene;
import javafx.scene.control.Menu;
import javafx.scene.control.MenuItem;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.BorderPane;
import javafx.stage.Screen;
import javafx.stage.Stage;
public class MainWindow extends Application {
private Stage primaryStage;
private BorderPane mainWindow;
@FXML
Menu menuFile, menuAnalysis;
@FXML
MenuItem menuNew;
@FXML
private void initialize() {
menuNew.setOnAction((event) -> {
try {
FXMLLoader loader = new FXMLLoader();
loader.setLocation(getClass().getResource("../view/AnchorTest.fxml"));
AnchorPane anchorTest = (AnchorPane) loader.load();
mainWindow.setCenter(anchorTest);
} catch (IOException e) {
e.printStackTrace();
}
});
}
@Override
public void start(Stage primaryStage) throws Exception {
this.primaryStage = primaryStage;
this.primaryStage.setTitle("Test Project");
initMainWindow();
}
public void initMainWindow() {
try {
FXMLLoader loader = new FXMLLoader();
loader.setLocation(getClass().getResource("../view/MainWindow.fxml"));
mainWindow = (BorderPane) loader.load();
Scene scene = new Scene(mainWindow);
primaryStage.setScene(scene);
//Fullscreen
Screen screen = Screen.getPrimary();
Rectangle2D bounds = screen.getVisualBounds();
primaryStage.setX(bounds.getMinX());
primaryStage.setY(bounds.getMinY());
primaryStage.setWidth(bounds.getWidth());
primaryStage.setHeight(bounds.getHeight());
primaryStage.setResizable(false);
primaryStage.show();
} catch (IOException e) {
e.printStackTrace();
}
}
}
main window.fxml
是一个边框窗格
,在顶部有一个菜单栏
代码:
当打开MainWindow.fxml
时,在我单击菜单File>Analysis>New
后,它应该将AnchorTest.fxml
内容放入MainWindow.fxml
中心。但是,我得到以下堆栈跟踪错误:
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at projecterror.controller.MainWindow.lambda$0(MainWindow.java:35)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.control.MenuItem.fire(MenuItem.java:462)
at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.doSelect(ContextMenuContent.java:1405)
at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.lambda$createChildren$343(ContextMenuContent.java:1358)
at com.sun.javafx.event.CompositeEventHandler$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$MouseEventNotification.run(GlassViewEventHandler.java:380)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:294)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:416)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:415)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:745)
标记NPE的行是:
mainWindow.setCenter(anchorTest);
我读过其他类似的问题,但大多数问题都与fxml文件的路径有关。我坚信这不是问题所在,因为在我的实际项目中,我对其他视图使用相同类型的路径,到目前为止我没有问题。
我已经上传了该项目,以防有人想运行该程序。
项目结构如下:
提前感谢,任何帮助都将不胜感激 启动JavaFX应用程序时,将创建应用程序类的实例,并且(在发生的其他事情中,start()
方法将在FX应用程序线程上的应用程序
实例上调用
加载FXML文件时,如果FXML文件指定了控制器类,则会创建该控制器类的实例,并将带注释的字段注入该实例,然后调用initialize()
方法。所有这些都发生在调用fxmloader.load()
的过程中
因此,在代码中,您将得到两个不同的MainWindow
实例。在一个实例上调用start()
方法,该方法初始化main窗口
字段,在另一个实例上调用initialize()
方法。由于第二个实例中从未初始化过mainWindow
,因此在initialize()
方法中尝试取消引用时,会出现空指针异常
将控制器类与应用程序
类分开。应用程序
类除了作为一个整体管理应用程序的生命周期之外,不应该做任何事情(通常,它应该实现启动应用程序所需的代码):
为了让控制器访问边框窗格
,您需要从FXML注入它(注意上面控制器代码中的注释)。将fx:id
添加到FXML文件中的元素:
启动JavaFX应用程序时,将创建应用程序类的实例,并且(在发生的其他事情中,start()
方法将在FX应用程序线程的应用程序
实例上调用
加载FXML文件时,如果FXML文件指定了控制器类,则会创建该控制器类的实例,并将带注释的字段注入该实例,然后调用initialize()
方法。所有这些都发生在调用fxmloader.load()
的过程中
因此,在代码中,您将得到两个不同的MainWindow
实例。在一个实例上调用start()
方法,该方法初始化main窗口
字段,在另一个实例上调用initialize()
方法。由于第二个实例中从未初始化过mainWindow
,因此在initialize()
方法中尝试取消引用时,会出现空指针异常
将控制器类与应用程序
类分开。应用程序
类除了作为一个整体管理应用程序的生命周期之外,不应该做任何事情(通常,它应该实现启动应用程序所需的代码):
为了让控制器访问边框窗格
,您需要从FXML注入它(注意上面控制器代码中的注释)。将fx:id
添加到FXML文件中的元素:
我从未见过JavaFX Main
以这种方式构造。您还应该发布项目的结构。Main窗口
未在控制器中初始化;它在启动应用程序时创建的应用程序
实例(调用start()
的实例)中初始化。这里的底线是,您不应该将应用程序类用作控制器类;这太令人困惑了(并且违反了各种基本的OOP设计原则,比如“单一责任”)。是的:创建一个单独的控制器类。您可以使用与访问其他元素完全相同的方式访问其中的边框窗格,即在FXML文件中为边框窗格指定一个fx:id
,并在控制器中创建一个相应的@FXML
-注释字段。指定重新打开。此处出现空指针异常是因为OP不知道他或她在不同的实例中初始化字段,而不是在访问字段的实例中初始化字段。标记为duplicate的问题无法解决此情况。我从未见过以这种方式构造的JavaFX Main
。您还应该发布项目的结构。mainWindow
未在控制器中初始化;它在启动应用程序时创建的应用程序
实例(调用start()
的实例)中初始化。这里的底线是,您不应该将应用程序类用作控制器类;这太令人困惑了(并且违反了各种基本的OOP设计原则)
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at projecterror.controller.MainWindow.lambda$0(MainWindow.java:35)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.control.MenuItem.fire(MenuItem.java:462)
at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.doSelect(ContextMenuContent.java:1405)
at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.lambda$createChildren$343(ContextMenuContent.java:1358)
at com.sun.javafx.event.CompositeEventHandler$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$MouseEventNotification.run(GlassViewEventHandler.java:380)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:294)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:416)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:415)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:745)
mainWindow.setCenter(anchorTest);
package projecterror.controller;
import java.io.IOException;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.geometry.Rectangle2D;
import javafx.scene.Scene;
import javafx.scene.layout.BorderPane;
import javafx.stage.Screen;
import javafx.stage.Stage;
public class MainWindow extends Application {
@Override
public void start(Stage primaryStage) throws Exception {
primaryStage.setTitle("Test Project");
initMainWindow(primaryStage);
}
public void initMainWindow(Stage primaryStage) {
try {
FXMLLoader loader = new FXMLLoader();
loader.setLocation(getClass().getResource("../view/MainWindow.fxml"));
BorderPane mainWindow = loader.load();
Scene scene = new Scene(mainWindow);
primaryStage.setScene(scene);
//Fullscreen
Screen screen = Screen.getPrimary();
Rectangle2D bounds = screen.getVisualBounds();
primaryStage.setX(bounds.getMinX());
primaryStage.setY(bounds.getMinY());
primaryStage.setWidth(bounds.getWidth());
primaryStage.setHeight(bounds.getHeight());
primaryStage.setResizable(false);
primaryStage.show();
} catch (IOException e) {
e.printStackTrace();
}
}
}
package projecterror.controller;
import java.io.IOException;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.control.Menu;
import javafx.scene.control.MenuItem;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.BorderPane;
public class MainWindowController {
@FXML
private BorderPane mainWindow;
@FXML
Menu menuFile, menuAnalysis;
@FXML
MenuItem menuNew;
@FXML
private void initialize() {
menuNew.setOnAction((event) -> {
try {
FXMLLoader loader = new FXMLLoader();
loader.setLocation(getClass().getResource("../view/AnchorTest.fxml"));
AnchorPane anchorTest = (AnchorPane) loader.load();
mainWindow.setCenter(anchorTest);
} catch (IOException e) {
e.printStackTrace();
}
});
}
}