在第一个控制器的第一个函数中，我从第二个控制器调用第二个函数，我得到了很多错误

Question

我有两个fxml文件，每个fxml文件都有一个控制器。在第一个fxml文件中，我有一个“基本”锚烷，在这个文件上有一个较小的“第二”锚烷。在第二个fxml文件中，我有一个“第三个”锚烷，它和第一个fxml中的“第二个”锚烷一样大。在这个“第三”锚烷上，我有一个桌面视图，比“第三”锚烷小一点。在第一个控制器中，我使用FXMLLoader将“second”anchorpane的内容设置为第二个fxml文件。在第一个控制器中，我有一个方法，将“第二个”锚烷的背景色设置为黄色，并从第二个控制器调用一个方法。这个方法（在第二个控制器中）希望使TableView更大，但我收到了错误消息。怎么了？

第一个控制器：

public class Controller implements Initializable {

@FXML
AnchorPane baseanc;
@FXML
AnchorPane ancpane2;
@FXML
Button button;

controller2 contr2 = new controller2();

public void testMethod() {
    ancpane2.setStyle("-fx-background-color: #ffff00");
    contr2.testFunc();
}

public void buttonAction(ActionEvent event) {
    testMethod();
}

@Override
public void initialize(URL url, ResourceBundle resourceBundle) {
    try {
        AnchorPane root = FXMLLoader.load(getClass().getResource("fxml2.fxml"));
        ancpane2.getChildren().setAll(root);
    } catch (IOException e) {
        e.printStackTrace();
    }
}
}

第二个控制器：

public class controller2{

@FXML
TableView table;

public void testFunc() {
    table.setPrefHeight(720);
} 
}

第一个fxml：

<AnchorPane fx:id="baseanc" xmlns="http://javafx.com/javafx/8.0.221" 
    xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
        <children>
          <AnchorPane fx:id="ancpane2" prefHeight="720.0" prefWidth="640.0"/>
          <Button fx:id="button" onAction="#buttonAction" text="Button" />
       </children>
    </AnchorPane>

第二个fxml：

  <AnchorPane fx:id="ancpane3" xmlns="http://javafx.com/javafx/8.0.221" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.controller2">
    <children>
     <TableView fx:id="table" prefHeight="600.0" prefWidth="540.0">
      <columns>
       <TableColumn prefWidth="75.0" text="C1" />
       <TableColumn prefWidth="75.0" text="C2" />
      </columns>
    </TableView>
  </children>
</AnchorPane>

错误消息：

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1787)
    at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1670)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
    at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8879)
    at javafx.controls/javafx.scene.control.Button.fire(Button.java:200)
    at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:206)
    at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3851)
    at javafx.graphics/javafx.scene.Scene$MouseHandler.access$1200(Scene.java:3579)
    at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1849)
    at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2588)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:397)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:434)
    at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:390)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:433)
    at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
    at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
    at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:76)
    at jdk.internal.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:273)
    at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:83)
    at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1782)
    ... 47 more
Caused by: java.lang.NullPointerException
    at sample.controller2.testFunc(controller2.java:13)
    at sample.Controller.testMethod(Controller.java:27)
    at sample.Controller.buttonAction(Controller.java:31)
    ... 58 more

Answer 1

问题在于，常规JavaFX控制器不应被视为单个实例（因为实际情况并非如此）。在加载FXML之后，所有与@FXML有关的内容都将只注入控制器

所以你叫“新控制员2”

public class controller2{

  @FXML
  TableView table;
  // Will be null without loading of a fxml

  public void testFunc() {
      table.setPrefHeight(720);
  } 
}

因此出现了空指针异常。

在初始化之后，您应该通过FXML加载器注入初始化的控制器。

//Initialize a loader FOR the fxml with the ressource as Constructor parameter
FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("fxml2.fxml"));
// then load!
AnchorPane root = fxmlLoader.load();
//Inject the Controller!

controller2= (Controller2) fxmlLoader.getController();
// in that order. 

那么fxml的初始化控制器应该是正确的实例。