You could see it on attached movie.

And you can use the next code:


import javafx.application.Application;
import javafx.event.Event;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.layout.Pane;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class Issue3 extends Application {

    public static void main(String[] args) {
        launch(args);
    }
    final ComboBox<String> testedComboBox = new ComboBox<String>();

    @Override
    public void start(Stage stage) throws Exception {
        Pane pane = new Pane();
        pane.setPrefHeight(200);
        pane.setPrefWidth(200);

        pane.getChildren().add(testedComboBox);

        testedComboBox.setVisibleRowCount(5);

        testedComboBox.setOnAction(new EventHandler() {

            public void handle(Event t) {
                System.out.println(testedComboBox.getValue());
            }
        });

        TextField tf = new TextField();
        //testedComboBox.valueProperty().bindBidirectional(tf.textProperty());
        testedComboBox.valueProperty().bind(tf.textProperty());

        VBox vb = new VBox();
        vb.getChildren().addAll(pane, tf);
        Scene scene = new Scene(vb, 400, 400);
        stage.setScene(scene);
        stage.show();
    }
}


Comment/uncomment according lines about binding to tf.textFieldProperty.
You could see difference in calling onAction on adding each symbol for bidirectional and unidirectional bindings:
bidirectional: listener is called for each symbol.
unidirectional: listener is not called.