Java fxml getController（）返回null

我是JavaFX的新手。有人能帮我吗

这是我的密码

Stage stage = new Stage();

FXMLLoader loader = new FXMLLoader();
Parent root = (Parent) loader.load(getClass().getResource("FXMLMain.fxml").openStream());
FXMLMainController mainController = loader.getController();
mainController.setStage(stage);
stage.setScene(new Scene(root));
stage.show();

((Node) (event.getSource())).getScene().getWindow().hide();

loader.getController（）返回null

java.lang.NullPointerException
    at library.management.system.FXMLDocumentController.loginButtonAction(FXMLDocumentController.java:69)
    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$MethodHandler.invoke(FXMLLoader.java:1763)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1651)
    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:204)
    at javafx.scene.Node.fireEvent(Node.java:8175)
    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:204)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3746)
    at javafx.scene.Scene$MouseHandler.access$1800(Scene.java:3471)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1695)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2486)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:314)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:243)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:345)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:526)
    at com.sun.glass.ui.View.notifyMouse(View.java:898)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.access$300(WinApplication.java:39)
    at com.sun.glass.ui.win.WinApplication$4$1.run(WinApplication.java:112)
    at java.lang.Thread.run(Thread.java:744)

---

将

fx:controller

属性添加到根项目，并给出控制器java文件名。 例如：如果根项目是

AnchorPane

和

FXMLMainController

控制器java文件，则

<AnchorPane fx:controller:"FXMLMainController">
</AnchorPane>

FXMLMain.fxml

add

fx:controller=“/folder/controllerjavafilename”

注意：我假设您的fxml和控制器文件位于同一位置。

这不起作用

FXMLLoader loader = new FXMLLoader();
loader.load(url);
FXMLController controller = loader.getController(); // return null

这项工作

FXMLLoader loader = new FXMLLoader(url);
FXMLController controller = loader.getController(); // return the controller

这很有效

FXMLLoader loader = new FXMLLoader();
loader.setLocation(Main.class.getResource(xmlNm+".fxml"));
Parent rootLayout = loader.load();
FXMLController controller = loader.getController();

---

我知道我的答案晚了，但我会让任何人受益谁将在这一页后下降

简短答复:

更改此项：

FXMLLoader loader = new FXMLLoader();
Parent root = (Parent) loader.load(getClass().getResource("FXMLMain.fxml").openStream());
FXMLMainController mainController = loader.getController();

为此：

FXMLLoader loader = new FXMLLoader(getClass().getResource("FXMLMain.fxml"));
Parent root = loader.load();
FXMLMainController mainController = loader.getController();

解释：

问题是您正在使用实例变量而不是FXMLLoader类调用load（）方法（这是一个静态方法）。 可以理解的是，您需要使用实例以便调用getController（）方法。在这种情况下，您应该在创建实例时将URL（使用getClass（）.getResource（））传递给FXMLLoader的构造函数，然后只需使用load（）方法即可获得父根。 方法调用的顺序是正确的，因此作为对其他方法的提醒，请记住您需要在getController（）之前首先调用load（）方法，否则它将返回null

---

我以前遇到过这个问题，我就是这样解决的。

FXMLMain.fxml文件在哪里？它是否位于java类所在的同一目录中？请尝试此操作。。。父根=（父）loader.load（getClass（）.getResource（“FXMLMain.fxml”）.toExternalForm（））；再看看这个。。。很可能，您的

按钮未在控制器中初始化@当然，我的FXMLMain.fxml位于java类所在的同一目录中。我还尝试了Parent root=（Parent）loader.load（getClass（）.getResource（“FXMLMain.fxml”）.toExternalForm（））；但是它向我显示了一个错误“找不到适合加载的方法（字符串）”你能解释一下为什么你的代码相对于被问的问题是有效的吗？这个答案可能让我省去了几个小时的沉思和自我怀疑。这是一个错误，糟糕的设计，还是有一个很好的理由呢？