BorderPane始终返回空值

Question

我正在处理JavaFX，我正在尝试将图形合成器从FXML页面添加到java类中，但是它总是返回null值

Page.fxml     

<?import javafx.scene.control.ScrollPane?>
<?import javafx.scene.layout.BorderPane?>

<ScrollPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" xmlns="http://javafx.com/javafx/8.0.172-ea" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
    <content>
        <BorderPane maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308"  fx:id="Mycontent">
            <top>
                <fx:include source="TopMenu.fxml" />
            </top>
         <center>
                <fx:include source="Operation.fxml" />
         </center>
         <left>
             <fx:include source="SideBar_Inhumer.fxml" />
         </left>
         <bottom>
             <fx:include source="Footer.fxml" />
         </bottom>
        </BorderPane>
    </content>
</ScrollPane>

Controller.java

package sample;

import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.scene.layout.BorderPane;
import java.net.URL;
import java.util.ResourceBundle;

public class Controller implements Initializable {
    @FXML
    public BorderPane Mycontent;

    @FXML
    public void goToDemandeur(){
        System.out.println(Mycontent);

        //Mycontent.setCenter(FXMLLoader.load(getClass().getResource("Demandeur.fxml")));
    }


    @Override
    public void initialize(URL location, ResourceBundle resources) {

    }
}

我的代码始终显示“空”

例如，如果我尝试使用Mycontent.getCenter()，则会出现此错误

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException

（这是正常的，因为Mycontent为null，但是为什么它为null？）

PS：单击goToDemandeur()后，我的方法SideBar_Inhumer.fxml被调用到另一个fxml页面onMouseClicked="#goToDemandeur"

SideBar_Inhumer.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.geometry.Insets?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.layout.Pane?>
<?import javafx.scene.layout.VBox?>
<?import javafx.scene.text.Font?>

<VBox layoutX="77.0" xmlns="http://javafx.com/javafx/8.0.172-ea" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
   <children>
       <Pane >
           <children>
               <Label alignment="CENTER" text="Inhumer" >
                   <font>
                      <Font size="24.0" />
                   </font>
                   <padding>
                       <Insets bottom="20.0" left="25.0" right="25.0" top="30.0"  />
                   </padding>
               </Label>
           </children>
       </Pane>
       <Pane style="-fx-background-color: #F08080;" onMouseClicked="#goToDemandeur">
           <children>
               <Label text="Demandeur" >
                   <font>
                       <Font size="15.0" />
                   </font>
               <padding>
                  <Insets bottom="10.0" left="20.0" right="20.0" top="10.0" />
               </padding>
               </Label>

           </children>
         <VBox.margin>
            <Insets />
         </VBox.margin>
       </Pane>
       <Pane style="-fx-background-color: #C6E2B9;">
           <children>
               <Label text="Defunt">
                   <font>
                       <Font size="15.0" />
                   </font>
                   <padding>
                       <Insets bottom="10.0" left="20.0" right="20.0" top="10.0" />
                   </padding>
               </Label>
           </children>
       </Pane>
       <Pane style="-fx-background-color: #FBF6A5;">
           <children>
               <Label text="Emplacement">
                   <font>
                       <Font size="15.0" />
                   </font>
                   <padding>
                       <Insets bottom="10.0" left="20.0" right="20.0" top="10.0" />
                   </padding>
               </Label>
           </children>
       </Pane>
       <Pane style="-fx-background-color: #FFCC99;">
           <children>
               <Label text="Prestataire">
                   <font>
                       <Font size="15.0" />
                   </font>
                   <padding>
                       <Insets bottom="10.0" left="20.0" right="20.0" top="10.0" />
                   </padding>
               </Label>
           </children>
       </Pane>
       <Pane style="-fx-background-color: #D8B46D;">
           <children>
               <Label text="Opération">
                   <font>
                       <Font size="15.0" />
                   </font>
                   <padding>
                       <Insets bottom="10.0" left="20.0" right="20.0" top="10.0" />
                   </padding>
               </Label>
           </children>
       </Pane>

   </children>
</VBox>

Main.java

    package View;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.geometry.Rectangle2D;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Screen;
import javafx.stage.Stage;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("../View/Page.fxml"));
        primaryStage.setTitle("Finalys");
        Screen screen = Screen.getPrimary();
        Rectangle2D bounds = screen.getVisualBounds();
        Scene scene =new Scene(root, 600, 475);
        primaryStage.setX(bounds.getMinX());
        primaryStage.setY(bounds.getMinY());
        primaryStage.setWidth(bounds.getWidth());
        primaryStage.setHeight(bounds.getHeight());
        primaryStage.setScene(scene);
        primaryStage.show();
        scene.getStylesheets().add(Main.class.getResource("bootstrap2.css").toExternalForm());


    }


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