java - Deselect an item on an javafx ListView on click

Question

I'm using a ListView control in a JavaFX application. It is set for MULTIPLE selection mode. I know as a user, I can Ctrl-Click an item to deselect it, but this is not intuitive enough for my users. I want a way to click a second time to deselect it. In other words click once - select; click selected item and it becomes unselected.

I've tried using both a ChangeListener and an onMouseClicked event. Neither works very well. Below are code snippets of each.

ChangeListener:

effect - first item in the list is NEVER selected. I click on it and it stays unclicked. No effect on items 2..n

listView.getSelectionModel().selectedItemProperty().addListener(new ChangeListener<SpecificAlgorithmData>() {
    @Override
    public void changed(final ObservableValue observableValue, final SpecificAlgorithmData oldData, final SpecificAlgorithmData newData) {

        //if already selected then deselect it
        int selectedIndex = listView.getSelectionModel().getSelectedIndex();
        System.out.println("selected " + selectedIndex);
        System.out.println("all selected" + listView.getSelectionModel().getSelectedIndices());
        if (!selecting && !listView.getSelectionModel().getSelectedIndices().contains(selectedIndex)){


            Iterator <Integer> iterator = listView.getSelectionModel().getSelectedIndices().iterator();
            selecting = true;
            listView.getSelectionModel().select(-1);//deselect all

            while (iterator.hasNext()){
                int index = iterator.next();
                if (index!= selectedIndex){
                    listView.getSelectionModel().select(index);
                }
            }
            selecting = false;
        }
    }
}

onClick:

No effect, since I'm not sure how to get the index of the one I just clicked. Being hard coded, this simply disallows of ever selecting item 2.

listView.setOnMouseClicked(new EventHandler<MouseEvent>() {
    @Override
    public void handle(final MouseEvent mouseEvent) {
        int selectedItem = 2; //FIXME: How to I get the index of clicked item?
        if (listView.getSelectionModel().isSelected(selectedItem)){
            listView.getSelectionModel().clearSelection(selectedItem);
        }
    }
});

Answer 1

Changing the behavior of controls in JavaFX is pretty difficult - there are really no hooks currently in the API into the behavior classes.

The following seems to work, by registering an event filter with the cells in the list, implementing the selection behavior directly, and consuming the event.

It feels a bit fragile though (what if a future release decided to implement the default behavior on mouse clicked, instead of mouse pressed, for example; or perhaps better, what if a future release decided to add additional functionality handled by mouse events). So use this solution with a bit of a "buyer beware" notice attached.

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.ListCell;
import javafx.scene.control.ListView;
import javafx.scene.control.MultipleSelectionModel;
import javafx.scene.control.SelectionMode;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;

public class DeselectableList extends Application {

    @Override
    public void start(Stage primaryStage) {
        ListView<String> list = new ListView<>();
        MultipleSelectionModel<String> selectionModel = list.getSelectionModel();
        selectionModel.setSelectionMode(SelectionMode.MULTIPLE);
        for (int i=1; i<=20; i++) {
            list.getItems().addAll("Item "+i);
        }
        list.setCellFactory(lv -> {
            ListCell<String> cell = new ListCell<>();
            cell.textProperty().bind(cell.itemProperty());
            cell.addEventFilter(MouseEvent.MOUSE_PRESSED, event -> {
                list.requestFocus();
                if (! cell.isEmpty()) {
                    int index = cell.getIndex();
                    if (selectionModel.getSelectedIndices().contains(index)) {
                        selectionModel.clearSelection(index);
                    } else {
                        selectionModel.select(index);
                    }
                    event.consume();
                }
            });
            return cell ;
        });
        BorderPane root = new BorderPane(list);
        Scene scene = new Scene(root, 150, 400);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

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

Obviously you know your users better than I, but I might prefer just to have a nice tooltip on the ListView explaining to them how to use it...