When I expand nodes, the node that I expand, sometimes changes its position. This is unusual (I have never seen this in any UI toolkit or application I have used so far) and problematic as far as the user experience is concerned.

I have attached a runnable test case.

To reproduce
- Start it
- expand the root node
- expand the node "19"
- scroll all the way down
- expand the node "194" it jumps up, which is the behavior I am trying to describe.


import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.scene.Scene;
import javafx.scene.control.TreeCell;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeView;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
import javafx.util.Callback;

import java.util.Random;

public class TreeTest extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception {
        final StackPane stackPane = new StackPane();
        final TreeView<Long> tree = new TreeView<>(new NumberTreeItem(1));
        tree.setCellFactory(new Callback<TreeView<Long>, TreeCell<Long>>() {
            @Override
            public TreeCell<Long> call(TreeView<Long> param) {
                return new TreeCell<Long>() {
                    @Override
                    protected void updateItem(Long item, boolean empty) {
                        super.updateItem(item, empty);
                        if (!empty) {
                            setText(item != null ? String.valueOf(item) : "");
                        } else{
                            setText(null);
                        }
                    }
                };
            }
        });
        stackPane.getChildren().add(tree);
        final Scene scene = new Scene(stackPane);
        primaryStage.setScene(scene);
        primaryStage.setTitle(getClass().getSimpleName());
        primaryStage.show();
    }

    private static class NumberTreeItem extends TreeItem<Long>{

        private boolean loaded = false;

        private NumberTreeItem(long value) {
            super(value);
        }

        @Override
        public boolean isLeaf() {
            return false;
        }

        @Override
        public ObservableList<TreeItem<Long>> getChildren() {
            if(!loaded){
                final ObservableList<TreeItem<Long>> children = super.getChildren();
                for (int i = 0; i < 10; i++) {
                    children.add(new NumberTreeItem(10 * getValue() + i));
                }
                loaded = true;
            }
            return super.getChildren();
        }
    }

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