我已经在JavaFX中为ListView实现了自定义ListCell，类似于以下教程：https://www.turais.de/how-to-custom-listview-cell-in-javafx/

我的ListCell包含3个元素，ImageView和2个带有一些描述的标签，这些描述是从数据库中加载的。因为我坚持使用MVC模式，所以ListUI fxml包含在mainUI fxml文件中。

运行程序并向下滚动列表视图时，出现以下错误消息：

javafx.fxml.LoadException: Root value already specified.
/D:/Semester%207/iExplore/iExplore/out/production/iExplore/listComponent/listcell.fxml
/D:/Semester%207/iExplore/iExplore/out/production/iExplore/listComponent/listcell.fxml
/D:/Semester%207/iExplore/iExplore/out/production/iExplore/listComponent/listcell.fxml

   at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2621)
   at javafx.fxml/javafx.fxml.FXMLLoader.createElement(FXMLLoader.java:2770)
   at javafx.fxml/javafx.fxml.FXMLLoader.processStartElement(FXMLLoader.java:2719)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2552)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2466)
   at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:2435)
   at listComponent.CustomListViewCell.updateItem(CustomListViewCell.java:50)

ListView Controller

import authentification.UserConnectionSingleton;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Alert;
import javafx.scene.control.ListView;
import models.Events;

import javax.persistence.EntityManager;
import javax.persistence.TypedQuery;
import java.net.URL;
import java.util.List;
import java.util.ResourceBundle;

public class ListController implements Initializable {

    @FXML
    private ListView<Events> EventList;
    private ObservableList<Events> eventsobservableList;
    private UserConnectionSingleton con;
    private EntityManager entityManager;
    private List<Events> tempList;

    public ListController(){
        try{
            con = UserConnectionSingleton.getInstance();
            entityManager = con.getManager();
            TypedQuery<Events> tq1 = entityManager.createNamedQuery("Events.findAllEvents",Events.class);
            tempList = tq1.getResultList();
            System.out.println(tempList.size());
            eventsobservableList = FXCollections.observableArrayList();
            eventsobservableList.addAll(tempList);
        } catch(Exception e){
            Alert alert = new Alert(Alert.AlertType.WARNING,"Check the internet connection...");
            alert.showAndWait();
            e.printStackTrace();
        }
    }

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

        EventList.setItems(eventsobservableList);
        EventList.setCellFactory(customListViewCell -> new CustomListViewCell());
    }
}

CustomCell Controller

import authentification.UserConnectionSingleton;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.control.Alert;
import javafx.scene.control.Label;
import javafx.scene.control.ListCell;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.HBox;
import models.Events;
import models.Location;
import models.Pictures;

import javax.persistence.EntityManager;

public class CustomListViewCell extends ListCell<Events> {

    @FXML
    private ImageView cellLogo;

    @FXML
    private Label descriptionLabel,locationLabel;

    @FXML
    private HBox boxLayout;
    private FXMLLoader loader;
    private Image image;
    private String imageURL;
    private int id;
    private UserConnectionSingleton con;
    private EntityManager entityManager;
    private String city;

    @Override
    protected void updateItem(Events event,boolean empty) {
        super.updateItem(event,empty);

        if(empty || event == null){
            setText(null);
            setGraphic(null);
        } else {
            if(loader == null){
                loader = new FXMLLoader(getclass().getResource("/listComponent/listcell.fxml"));
                loader.setController(this);
            }

            try{
                loader.load();
                con = UserConnectionSingleton.getInstance();
                entityManager = con.getManager();
            } catch(Exception e){
                Alert alert = new Alert(Alert.AlertType.WARNING,"Check the internet connection...");
                alert.showAndWait();
                e.printStackTrace();
            }

            id = event.getId();
            imageURL = entityManager.find(Pictures.class,id).getLogo();
            city = entityManager.find(Location.class,id).getcity();
            System.out.println(imageURL);
            image = new Image(imageURL);
            cellLogo = new ImageView(image);

            descriptionLabel.setText(event.getShortDescription());
            locationLabel.setText(city);

            setText(null);
            setGraphic(boxLayout);
        }

    }
}

ListView Fxml

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

<?import javafx.scene.control.ListView?>
<?import javafx.scene.effect.ColorAdjust?>
<?import javafx.scene.layout.VBox?>

<VBox fx:id="listLayout" alignment="CENTER" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="328.0" prefWidth="543.0" xmlns="http://javafx.com/javafx/8.0.172-ea" xmlns:fx="http://javafx.com/fxml/1" fx:controller="listComponent.ListController">
   <effect>
      <ColorAdjust />
   </effect>
   <children>
      <ListView fx:id="EventList" prefHeight="365.0" prefWidth="821.0" />
   </children>
</VBox>

自定义ListCell FXML

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

<?import javafx.geometry.Insets?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.image.ImageView?>
<?import javafx.scene.layout.HBox?>
<?import javafx.scene.layout.VBox?>

<HBox fx:id="boxLayout" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="177.0" prefWidth="534.0" xmlns="http://javafx.com/javafx/8.0.172-ea" xmlns:fx="http://javafx.com/fxml/1">
   <children>
      <ImageView fx:id="cellLogo" fitHeight="166.0" fitWidth="165.0" pickOnBounds="true" preserveRatio="true" />
      <VBox alignment="CENTER" prefHeight="160.0" prefWidth="259.0">
         <children>
            <Label fx:id="descriptionLabel" text="Label" />
         </children>
      </VBox>
      <VBox alignment="BOTTOM_RIGHT" prefHeight="165.0" prefWidth="127.0">
         <children>
            <Label fx:id="locationLabel" text="Label" />
         </children>
      </VBox>
   </children>
   <padding>
      <Insets bottom="10.0" left="5.0" top="10.0" />
   </padding>
</HBox>