为什么在我从ListView和相应的ObservableList中删除一个项之后，数据仍然保留？

Question

我正在使用javafx创建一个ListView，允许用户添加、签出、签入和删除ListView的元素。但是，当一个元素被删除，另一个元素被放到它的位置时，程序的作用就好像删除的元素仍然存在，如果我尝试签出新添加的元素，它会检查出我刚才尝试删除的元素。

简单地说，这就是发生的事情：

添加->“项目1”

添加->“第2项”

删除->“项目1”(项目1现在被删除，项目2在ViewList中向上移动)

签出->“项目2”(出现一个提示，允许用户说明签出项目的对象和签出日期)

在用户填写信息后，该行现在将"item 1签出为"name“on”date“。”

它应该说第二项而不是第一项，我不知道为什么要这样做。

LibraryGUI.java

import java.util.ArrayList;
import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ListView;
import javafx.scene.control.SelectionMode;
import javafx.scene.control.TextField;
import javafx.scene.control.cell.ChoiceBoxListCell;
import javafx.scene.layout.Pane;
import javafx.scene.text.Text;
import javafx.stage.Stage;

public class LibraryGUI extends Application implements EventHandler<ActionEvent> {
    private Library lib = new Library();
    private ObservableList<String> item = FXCollections.observableArrayList();
    private ListView<String> items = new ListView<String>(item);
    private ArrayList<String> titles = new ArrayList<String>();
    private ArrayList<String> formats = new ArrayList<String>();
    private String title, format, loanedTo, dateLoaned;
    private Button add, checkOut, checkIn, delete, accept1, accept2, accept3, accept4, cancel1, cancel2, cancel3,
            cancel4;
    private TextField tf1, tf2, tf3, tf4;
    private Stage stage1, stage2, stage3, stage4;
    private int itemNum;

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

    @Override
    public void start(Stage primaryStage) throws Exception {
        LibraryGUI gui = new LibraryGUI();
        primaryStage.setTitle("Personal Lending Library");
        items.getSelectionModel().setSelectionMode(SelectionMode.SINGLE);
        Scene scene = new Scene(gui.layout(), 325, 340);
        primaryStage.setScene(scene);
        primaryStage.show();

    }

    public Pane layout() {

        add = new Button("Add");
        add.setOnAction(this);
        add.setLayoutX(5);
        add.setLayoutY(310);
        add.setPrefWidth(75);

        checkOut = new Button("Check Out");
        checkOut.setOnAction(this);
        checkOut.setLayoutX(85);
        checkOut.setLayoutY(310);
        checkOut.setPrefWidth(75);

        checkIn = new Button("Check In");
        checkIn.setOnAction(this);
        checkIn.setLayoutX(165);
        checkIn.setLayoutY(310);
        checkIn.setPrefWidth(75);

        delete = new Button("Delete");
        delete.setOnAction(this);
        delete.setLayoutX(245);
        delete.setLayoutY(310);
        delete.setPrefWidth(75);

        Pane layout = new Pane();
        items.setItems(item);
        items.setCellFactory(ChoiceBoxListCell.forListView(item));
        items.setLayoutX(5);
        items.setLayoutY(5);
        items.setPrefWidth(315);
        items.setPrefHeight(300);
        layout.getChildren().addAll(items, add, checkOut, checkIn, delete);
        return layout;
    }

    @Override
    public void handle(ActionEvent event) {
        if (event.getSource() == add) {

            accept1 = new Button("Accept");
            accept1.setPrefWidth(70);
            accept1.setLayoutX(125);
            accept1.setLayoutY(65);
            accept1.setOnAction(this);
            cancel1 = new Button("Cancel");
            cancel1.setPrefWidth(70);
            cancel1.setLayoutX(205);
            cancel1.setLayoutY(65);
            cancel1.setOnAction(this);

            Text dialog = new Text("Media Item Name:");
            dialog.setLayoutX(20);
            dialog.setLayoutY(45);

            tf1 = new TextField();
            tf1.setPrefHeight(20);
            tf1.setPrefWidth(150);
            tf1.setLayoutX(125);
            tf1.setLayoutY(30);

            Pane layout1 = new Pane();
            layout1.getChildren().addAll(tf1, dialog, accept1, cancel1);

            stage1 = new Stage();
            stage1.setTitle("Item Name");
            stage1.setScene(new Scene(layout1, 400, 100));
            stage1.show();
        }

        if (event.getSource() == cancel1) {
            stage1.close();
        }

        if (event.getSource() == accept1) {
            title = tf1.getText();
            titles.add(tf1.getText());
            stage1.close();

            accept2 = new Button("Accept");
            accept2.setPrefWidth(70);
            accept2.setLayoutX(125);
            accept2.setLayoutY(65);
            accept2.setOnAction(this);
            cancel2 = new Button("Cancel");
            cancel2.setPrefWidth(70);
            cancel2.setLayoutX(205);
            cancel2.setLayoutY(65);
            cancel2.setOnAction(this);

            Text dialog = new Text("Media Item Format:");
            dialog.setLayoutX(15);
            dialog.setLayoutY(45);

            tf2 = new TextField();
            tf2.setPrefHeight(20);
            tf2.setPrefWidth(150);
            tf2.setLayoutX(125);
            tf2.setLayoutY(30);
            format = tf2.getText();

            Pane layout2 = new Pane();
            layout2.getChildren().addAll(tf2, dialog, accept2, cancel2);

            stage2 = new Stage();
            stage2.setTitle("Item Format");
            stage2.setScene(new Scene(layout2, 400, 100));
            stage2.show();
        }

        if (event.getSource() == cancel2) {
            title = null;
            titles.remove(titles.size() - 1);
            stage2.close();
        }

        if (event.getSource() == accept2) {
            format = tf2.getText();
            formats.add(tf2.getText());
            lib.addNewItem(title, format);
            items.getItems().add(title + " (" + format + ")");
            stage2.close();

        }

        if (event.getSource() == checkOut) { //item is being checked out
            item = items.getSelectionModel().getSelectedItems();

            for (int i = 0; i < items.getItems().size(); i++) {
                if (items.getSelectionModel().getSelectedItem()
                        .equals(lib.getItemList().get(i).getTitle() + " (" + lib.getItemList().get(i).getFormat() + ")")

                        && !lib.getItemList().get(i).onLoan) {
                    itemNum = i;

                    accept3 = new Button("Accept");
                    accept3.setPrefWidth(70);
                    accept3.setLayoutX(125);
                    accept3.setLayoutY(65);
                    accept3.setOnAction(this);
                    cancel3 = new Button("Cancel");
                    cancel3.setPrefWidth(70);
                    cancel3.setLayoutX(205);
                    cancel3.setLayoutY(65);
                    cancel3.setOnAction(this);

                    Text dialog = new Text("Loaned To:");
                    dialog.setLayoutX(60);
                    dialog.setLayoutY(45);

                    tf3 = new TextField();
                    tf3.setPrefHeight(20);
                    tf3.setPrefWidth(150);
                    tf3.setLayoutX(125);
                    tf3.setLayoutY(30);

                    Pane layout3 = new Pane();
                    layout3.getChildren().addAll(accept3, cancel3, dialog, tf3);

                    stage3 = new Stage();
                    stage3.setTitle("Check Out");
                    stage3.setScene(new Scene(layout3, 400, 100));
                    stage3.show();

                }
            }
        }

        if (event.getSource() == accept3) {
            loanedTo = tf3.getText();
            lib.getItemList().get(itemNum).loanedTo = loanedTo;
            stage3.close();

            accept4 = new Button("Accept");
            accept4.setPrefWidth(70);
            accept4.setLayoutX(125);
            accept4.setLayoutY(65);
            accept4.setOnAction(this);
            cancel4 = new Button("Cancel");
            cancel4.setPrefWidth(70);
            cancel4.setLayoutX(205);
            cancel4.setLayoutY(65);
            cancel4.setOnAction(this);

            Text dialog = new Text("Date Loaned:");
            dialog.setLayoutX(50);
            dialog.setLayoutY(45);

            tf4 = new TextField();
            tf4.setPrefHeight(20);
            tf4.setPrefWidth(150);
            tf4.setLayoutX(125);
            tf4.setLayoutY(30);

            Pane layout3 = new Pane();
            layout3.getChildren().addAll(accept4, cancel4, dialog, tf4);

            stage4 = new Stage();
            stage4.setTitle("Check Out");
            stage4.setScene(new Scene(layout3, 400, 100));
            stage4.show();

        }

        if (event.getSource() == accept4) {
            stage4.close();
            dateLoaned = tf4.getText();
            lib.getItemList().get(items.getSelectionModel().getSelectedIndex()).dateLoaned = dateLoaned;
            lib.getItemList().get(items.getSelectionModel().getSelectedIndex()).onLoan = true;

            items.getItems().set(items.getSelectionModel().getSelectedIndex(),
                    titles.get(items.getSelectionModel().getSelectedIndex()) + " ("
                            + formats.get(items.getSelectionModel().getSelectedIndex()) + ") loaned to " + loanedTo
                            + " on " + dateLoaned);
        }

        if (event.getSource() == checkIn) {
            for (int i = 0; i < items.getItems().size(); i++) {
                if (items.getSelectionModel().getSelectedItem().contains(lib.getItemList().get(i).getTitle())
                        && items.getSelectionModel().getSelectedItem().contains(lib.getItemList().get(i).getFormat())
                        && lib.getItemList().get(i).onLoan) {
                    itemNum = i;
                    items.getItems().set(items.getSelectionModel().getSelectedIndex(),
                            titles.get(items.getSelectionModel().getSelectedIndex()) + " ("
                                    + formats.get(items.getSelectionModel().getSelectedIndex()) + ")");

                    lib.getItemList().get(items.getSelectionModel().getSelectedIndex()).dateLoaned = null;
                    lib.getItemList().get(items.getSelectionModel().getSelectedIndex()).onLoan = false;

                }
            }
        }

        if (event.getSource() == delete) { //item is being deleted from all lists
            items.getItems().remove(items.getSelectionModel().getSelectedIndex());
            for (int i = 0; i < items.getItems().size(); i++) {
                if (items.getSelectionModel().getSelectedItem().contains(lib.getItemList().get(i).getTitle())
                        && items.getSelectionModel().getSelectedItem().contains(lib.getItemList().get(i).getFormat())) {
                    itemNum = i;
                    lib.getItemList().remove(items.getSelectionModel().getSelectedIndex());
                    items.getItems().remove(items.getSelectionModel().getSelectedIndex());
                    titles.remove(items.getSelectionModel().getSelectedIndex());
                    formats.remove(items.getSelectionModel().getSelectedIndex());

                }
            }
        }

    }

}

Library.java

import javafx.collections.FXCollections;
import javafx.collections.ObservableList;

public class Library {

    private ObservableList<MediaItem> item = FXCollections.observableArrayList();

    public ObservableList<MediaItem> getItemList() {
        return item;
    }

    void addNewItem(String title, String format) {
        item.add(new MediaItem(title, format));

    }

我最近才开始用Java编程，所以我的代码很可能不是很优化。任何和所有的帮助都将不胜感激。谢谢。

Answer 1

这不是一个完整的答案，因为我没有运行您的代码，但看看它，我有几个建议给您。

首先，让您的整个类都是一个ActionEvent，并且拥有一个单独的“句柄”方法可能并不理想。我会将该handle方法拆分为不同的方法，命名为这个public void handleAdd(ActionEvent event)，并将它们添加到类似于这个add.setOnAction((ActionEvent e) -> handleAdd(e));的按钮中。这更有意义，因为每个按钮都有一个与其关联的特定操作，并且该操作包含在特定的方法中。

其次，您需要四个列表和一个Library对象(它看起来只是另一个列表的包装器)吗？你试图让五个不同的列表保持同步，这必然会导致像你现在看到的那样的问题，也会让你头疼，或者谁将来不得不阅读和维护代码。相反，考虑让您的库使用ListView类型的MediaItem而不是String，并将loanedto和数据作为MediaItem的属性添加，假设这是您自己编写的类。通过设置这样的单元格工厂，您仍然可以在ListView中正确地显示标题：

items.setCellFactory(new Callback<ListView<MediaItem>, ListCell<MediaItem>>() {
    @Override
    public ListCell<MediaItem> call(ListView<MediaItem> param) {
        return new ListCell<MediaItem>() {
            @Override
            protected void updateItem(MediaItem item, boolean empty) {
                super.updateItem(item, empty);
                if(item != null) {
                    setText(item.getTitle());
                }else{
                    setText("");
                }
            }
        };
    }
});