javafx - 表视图的 IndexOutOfBoundsException

Question

I would to ask why does IndexOutOfBoundsException appear when I try to delete the first row from the table view of supplement which is index 0. I am using a button to delete the row

Update: update the code to have a minimal reproducible example

SupplementTest.java

public class SupplementTest extends Application {

    WindowController windowGUI = new WindowController();
    Stage stageGUI;
    Scene sceneGUI;

    @Override
    public void start(Stage primaryStage) throws IOException {

        FXMLLoader assignment2 = new FXMLLoader(getClass().getResource("SupplementFXML.fxml"));
        Parent fxmlFile = assignment2.load();

        try {
            stageGUI = primaryStage;
            windowGUI.initialize();

            sceneGUI = new Scene(fxmlFile, 250, 350);

            stageGUI.setScene(sceneGUI);
            stageGUI.setTitle("Supplement");
            stageGUI.show();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

WindowController.java

public class WindowController {

    Stage newWindow = new Stage();
    boolean deleteSupplement;

    @FXML
    private GridPane primaryGrid = new GridPane();
    @FXML
    private Label supplementLabel = new Label();
    @FXML
    private Button deleteBtn = new Button(), addBtn = new Button();
    public TableView<Supplement> supplementView = new TableView<>();

    int suppIndex;
    ArrayList<Supplement> supplementList = new ArrayList<>();

    // initialize Method
    public void initialize() {
        newWindow.initModality(Modality.APPLICATION_MODAL);
        newWindow.setOnCloseRequest(e -> e.consume());
        initializeWindow();
        updateSupplementList();
    }

    public void initializeWindow() {

        deleteSupplement = false;

        TableColumn<Supplement, String> suppNameColumn = new TableColumn<>("Name");
        suppNameColumn.setCellValueFactory(new PropertyValueFactory<>("supplementName"));
        TableColumn<Supplement, Double> suppCostColumn = new TableColumn<>("Weekly Cost");
        suppCostColumn.setCellValueFactory(new PropertyValueFactory<>("weeklyCost"));
        supplementView.getColumns().addAll(suppNameColumn, suppCostColumn);
        supplementView.setColumnResizePolicy(TableView.CONSTRAINED_RESIZE_POLICY);

        suppIndex = supplementView.getSelectionModel().getSelectedIndex();

        addBtn.setOnAction(e -> {
            supplementList.add(new Supplement("Test1", 10));
            supplementList.add(new Supplement("Test2", 20));
            supplementList.add(new Supplement("Test3", 15));
            updateSupplementList();
        });

        // remove button
        deleteBtn.setOnAction(e -> {
            deleteSupplement = true;
            deleteSupplement();
        });
    }

    public void updateSupplementList() {
        supplementView.getItems().clear();

        if (supplementList.size() > 0) {
            for(int i = 0; i < supplementList.size(); i++) {
                Supplement supplement = new Supplement(supplementList.get(i).getSupplementName(),
                        supplementList.get(i).getWeeklyCost());
                supplementView.getItems().add(supplement);
            }
        }
    }

    public void deleteSupplement() {
        try {
            ObservableList<Supplement> supplementSelected, allSupplement;
            allSupplement = supplementView.getItems();
            supplementSelected = supplementView.getSelectionModel().getSelectedItems();
            supplementSelected.forEach(allSupplement::remove);
            supplementList.remove(suppIndex);
        } catch(Exception ex) {
            ex.printStackTrace();
        }
    }
}

Supplement.java

public class Supplement implements Serializable {

    private String supplementName;
    private double weeklyCost;

    public Supplement() {
        this.supplementName = "";
        this.weeklyCost = 0.00;
    }

    public Supplement(String suppName, double weeklyCost) {
        this.supplementName = suppName;
        this.weeklyCost = weeklyCost;
    }

    public String getSupplementName() {
        return supplementName;
    }

    public double getWeeklyCost() {
        return weeklyCost;
    }

    public void setSupplementName(String supplementName) {
        this.supplementName = supplementName;
    }

    public void setWeeklyCost(double weeklyCost) {
        this.weeklyCost = weeklyCost;
    }

}

How do I fix it so that when I delete any index in the table view the IndexOutOfBoundsException does not appear?

Answer 1

It's difficult to know for certain what is causing the exception, because your code is both incomplete (so no-one here can copy, paste, and run it to reproduce the error), and very confusing (it is full of seemingly-unnecessary code). However:

You seem to be doing two different things to delete the selected item(s) from the table:

supplementSelected = supplementView.getSelectionModel().getSelectedItems();
supplementSelected.forEach(allSupplement::remove);

which is an attempt to delete all selected items (though I don't believe it will work if more than one item is selected)

and

supplementList.remove(suppIndex);

which will delete the selected item, as defined by the selected index property in the selection model . (It is the currently selected item in a single selection model, or the last selected item in a multiple selection model, or -1 if nothing is selected.)

The latter will not work, because you only ever set suppIndex in your initialization code:

public void initializeWindow() {

    // ...

    suppIndex = supplementView.getSelectionModel().getSelectedIndex();

    // ...
}

Of course, when this code is executed, the user has not had a chance to selected anything (the table isn't even displayed at this point), so nothing is selected, and so suppIndex is assigned -1 . Since you never change it, it is always -1 , and so when you call

supplementList.remove(suppIndex);

you get the obvious exception.

If you are only supporting single selection, and want to delete the currently selected item (or the last selected item in multiple selection), just get the selection at the time. You probably still want to check something is selected:

public void deleteSupplement() {
    int selectedIndex = supplementView.getSelectionModel().getSelectedIndex();
    if (selectedIndex >= 0) {
        supplementView.getItems().remove(selectedIndex);
    }
}

A slight variation on this, which I think is preferable, is to work with the actual object instead of its index:

public void deleteSupplement() {
    Supplement selection = supplementView.getSelectionModel().getSelectedItem();
    if (selection != null) {
        supplementView.getItems().remove(selection);
    }
}

Now, of course (in a theme that is common to a lot of your code), you can remove suppIndex entirely; it is completely redundant.

If you want to support multiple selection, and delete all selected items, then the code you currently have for that will cause an issue if more than one item is selected. The problem is that if a selected item is removed from the table's items list, it will also be removed from the selection model's selected items list. Thus, the selected items list ( supplementSelected ) in your code changes while you are iterating over it with forEach(...) , which will throw a ConcurrentModificationException .

To avoid this, you should copy the list of selected items into another list, and remove those items:

public void deleteSupplement() {
    List<Supplement> selectedItems
        = new ArrayList<>(supplementView.getSelectionModel().getSelectedItems());
    supplementView.getItems().removeAll(selectedItems);
}

Of course, this code also works with single selection (when the list is always either length 0 or length 1).

---

To address a couple of other issues: there is really no point in keeping a separate list of Supplement items. The table already keeps that list, and you can reference it at any time with supplementView.getItems() . (If you wanted to reference the list elsewhere, eg in a model in a MVC design, you should make sure that there is just a second reference to the existing list; don't create a new list.)

In particular, you should not rebuild the table entirely from scratch every time you add a new item to the list. Get rid of the redundant supplementList entirely from your code. Get rid of updateSupplementList() entirely; it is firstly doing way too much work, and secondly (and more importantly) will replace all the existing items just because you add a new one. This will lost important information (for example it will reset the selection).

To add new items, all you need is

    addBtn.setOnAction(e -> {
        supplementView.getItems().add(new Supplement("Test1", 10));
        supplementView.getItems().add(new Supplement("Test2", 20));
        supplementView.getItems().add(new Supplement("Test3", 15));
    });

There are various other parts of your code that don't make any sense, such as:

• The deleteSupplement variable. This seems to have no purpose.
• The try - catch in the deleteSupplement method. The only exceptions that can be thrown here are unchecked exceptions caused by programming logic errors (such as the one you see). There is no point in catching those; you need to fix the errors so the exceptions are not thrown.
• The @FXML annotations. You should never initialize fields that are annotated @FXML . This annotation means that the FXMLLoader will initialize these fields. In this case (as far as I can tell) these are not even associated with an FXML file at all, so the annotation should be removed.