JavaFX: Adding CTRL-click functionality to checkboxes of nested CheckBoxTreeItem[s]

Question

I have a situation where a TreeView is being displayed, with two levels of entries (parents and children), like so:

root (invisible)
|_ parent item 1
   |_ child item 1-1
   |_ child item 1-2
|_ parent item 2
   |_ child item 2-1

These items are all standard CheckBoxTreeItems. What I want to do, is to have CTRL-clicking on a parent item's checkbox select a set of it's children, according to some function. For example, here I might want only the first child item (i.e. child item 1-1 and child item 2-1) in each child list to be selected upon CTRL-clicking the parent checkbox.

Is this possible? As far as I can see, there's no good way to access the checkbox and give it e.g. an onMouseClick event handler, which is the solution that would make sense to me.

The code for the example tree layout given above:

TreeViewTest.java

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.CheckBoxTreeItem;
import javafx.scene.control.TreeView;
import javafx.scene.control.cell.CheckBoxTreeCell;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class TreeViewTest extends Application {

    @Override
    public void start(final Stage stage) {
        StackPane sceneRoot = new StackPane();

        // create the tree model
        CheckBoxTreeItem<String> parent1 = new CheckBoxTreeItem<>("parent 1");
        CheckBoxTreeItem<String> parent2 = new CheckBoxTreeItem<>("parent 2");
        CheckBoxTreeItem<String> child1_1 = new CheckBoxTreeItem<>("child 1-1");
        CheckBoxTreeItem<String> child1_2 = new CheckBoxTreeItem<>("child 1-2");
        CheckBoxTreeItem<String> child2_1 = new CheckBoxTreeItem<>("child 2-1");
        CheckBoxTreeItem<String> root = new CheckBoxTreeItem<>("root");

        // attach the nodes
        parent1.getChildren().addAll(child1_1, child1_2);
        parent2.getChildren().addAll(child2_1);
        root.getChildren().addAll(parent1, parent2);

        // display everything
        root.setExpanded(true);
        parent1.setExpanded(true);
        parent2.setExpanded(true);

        // create the treeView
        final TreeView<String> treeView = new TreeView<>();
        treeView.setShowRoot(false);
        treeView.setRoot(root);

        // set the cell factory
        treeView.setCellFactory(CheckBoxTreeCell.forTreeView());

        // display the tree
        sceneRoot.getChildren().addAll(treeView);
        Scene scene = new Scene(sceneRoot, 200, 200);
        stage.setScene(scene);
        stage.show();
    }

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

You need to implement the TreeCell yourself, instead of using the convenience implementation CheckBoxTreeCell (which doesn't give you access to the CheckBox, as you noted). Since you know your tree items are CheckBoxTreeItems, and you are only working with String as their type, this is not too difficult. — James_D
@James_D that's what I feared. I tried to make a copy of CheckBoxTreeCell to tack onto the javafx package (wanting to change the minimum amount of the code, given that I'm largely unsure what it does), and got an IllegalAccessException about not being able to access the superclass DefaultTreeCell from my CustomCBTC. I think that's more a problem with my understanding of Java as a whole, though (logically I don't see why this shouldn't work, but hey ho). Anyway, tried again, minimally copying code from CBTC into a new class in my own package, and it seems to work, so, thanks! — Murray

James_D James_D · Accepted Answer · 2017-02-03T13:54:48

You need a custom implementation of TreeCell. This should give you a starting point that allows you to implement the additional functionality you need:

public class MyCheckBoxCell extends TreeCell<String> {

    private final CheckBox checkBox = new CheckBox();

    private BooleanProperty currentSelectedBinding ;

    // only need this if you are using the indeterminateProperty() of your
    // CheckBoxTreeItems
    private BooleanProperty currentIndeterminateBinding ;

    public MyCheckBoxCell() {

        // add extra event handling to the check box here...

    }

    @Override
    protected void updateItem(String item, boolean empty) {

        super.updateItem(item, empty);

        if (empty) {
            setText(null);
            setGraphic(null);
        } else {
            setText(item);
            setGraphic(checkBox);
            if (currentSelectedBinding != null) {
                checkBox.selectedProperty().unbindBidirectional(currentSelectedBinding);
            }
            if (currentIndeterminateBinding != null) {
                checkBox.indeterminateProperty().unbindBidirectional(currentIndeterminateBinding);
            }
            if (getTreeItem() instanceof CheckBoxTreeItem) {
                CheckBoxTreeItem cbti = (CheckBoxTreeItem<?>) getTreeItem();
                currentSelectedBinding = cbti.selectedProperty();
                checkBox.selectedProperty().bindBidirectional(currentSelectedBinding);
                currentIndeterminateBinding = cbti.indeterminateProperty();
                checkBox.indeterminateProperty().bindBidirectional(currentIndeterminateBinding);
            }
        }
    }
}

JavaFX: Adding CTRL-click functionality to checkboxes of nested CheckBoxTreeItem[s]

2 Answers