尽管使用了fx：ids，FXML变量显示为null

我是初学者，我正在尝试构建一个简单的字典应用程序 .

我有一个控制器类，它有一个按钮来打开一个新的对话框来输入各种细节 .

该对话框由一个单独的控制器控制，这是我遇到问题的地方，我的FXML元素被赋予null值，因此当我运行代码时，我得到一个nullpointerexception . 我用@FXML注释了FXML vaiables并检查了fxml文件中的fx：id是否与java文件的fx：id相匹配 .

Here is the Controller.java code:

package sample;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.control.ButtonType;
import javafx.scene.layout.BorderPane;
import javafx.scene.control.Dialog;

import java.io.IOException;
import java.util.Optional;

public class Controller {

@FXML
private BorderPane mainBorderPane;
@FXML
private DialogController controller = new DialogController();
@FXML
public void initialize(){

}

@FXML
public void newItemDialog(){
    Dialog <ButtonType> dialog = new Dialog<>();
    dialog.initOwner(mainBorderPane.getScene().getWindow());
    dialog.setTitle("Insert Word");
    FXMLLoader fxmlLoader = new FXMLLoader();
    fxmlLoader.setLocation(getClass().getResource("newDialog.fxml"));
    try{
        dialog.getDialogPane().setContent(fxmlLoader.load());
    }catch(IOException e) {
        e.printStackTrace();
        return;
    }
    dialog.getDialogPane().getButtonTypes().add(ButtonType.OK);
    dialog.getDialogPane().getButtonTypes().add(ButtonType.CANCEL);
    Optional<ButtonType> result = dialog.showAndWait();
    if(result.isPresent() && result.get() == ButtonType.OK){
        boolean results = controller.processResults();

    }else{
        System.out.println("Cancelled");
        return;
    }
}
}

Here is the DialogController.java code:

package sample;

import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import sample.control.Data;

import java.io.IOException;
import java.util.Optional;

public class DialogController {
@FXML
private TextField nameField;
@FXML
private TextField descriptionField;
@FXML
private TextField typeField;
@FXML
private TextField sentenceField;


@FXML
public boolean processResults() {

    String name = nameField.getText();
    String description = descriptionField.getText();
    String type = typeField.getText();
    String sentence = sentenceField.getText();

    return Data.getInstance().addWord(name,type,description,sentence);
    }    
}

Here is the sample.fxml code:

<?import javafx.scene.layout.BorderPane?>
<?import javafx.scene.control.MenuBar?>
<?import javafx.scene.control.Menu?>
<?import javafx.scene.control.MenuItem?>
<?import javafx.scene.control.ListView?>
<?import java.lang.String?>
<?import javafx.scene.control.TextArea?>
<?import javafx.scene.layout.VBox?>
<BorderPane fx:controller="sample.Controller"
        xmlns:fx="http://javafx.com/fxml"
        fx:id ="mainBorderPane">

<top>
    <MenuBar>

        <Menu fx:id="fileButton" text="File">
            <MenuItem fx:id="newButton" onAction="#newItemDialog" text="New"/>
            <MenuItem fx:id="updateButton" text="Update"/>
            <MenuItem fx:id="deleteButton" text="Delete"/>
            <MenuItem fx:id="saveButton" text="Save"/>
        </Menu>
        <Menu fx:id="viewButton" text="View">
            <MenuItem text="Dark Mode"/>
        </Menu>
    </MenuBar>
</top>
<left>
    <ListView fx:id="wordListView" BorderPane.alignment="TOP_LEFT" prefHeight="Infinity" prefWidth="250">

    </ListView>
</left>
<center>
    <VBox>
        <TextArea fx:id = "wordDetails" prefWidth="Infinity" prefHeight="400">

        </TextArea>
        <TextArea prefWidth="Infinity" prefHeight="200">

        </TextArea>
    </VBox>
</center>

</BorderPane>

Here is the newDialog.fxml code:

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

<?import java.lang.*?>
<?import java.util.*?>
<?import javafx.scene.*?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.layout.*?>

<?import javafx.scene.text.Text?>
<?import javafx.scene.control.DialogPane?>
<DialogPane xmlns="http://javafx.com/javafx"
        xmlns:fx="http://javafx.com/fxml"
        fx:controller="sample.DialogController"
        prefHeight="400.0" prefWidth="600.0">
<headerText>
    Enter A Word
</headerText>
<content>
    <VBox>
        <TextField fx:id="nameField" promptText="Enter the word"/>
        <TextField fx:id="typeField" promptText="Enter the type"/>
        <TextField fx:id="descriptionField" promptText="Enter a description"/>
        <TextField fx:id="sentenceField" promptText="Enter a sentence"/>
    </VBox>
</content>

提前致谢！