JavaFX: automatically expand ChoiceBox when on focus - javafx-8

Question

I have a ChoiceBox for which I want to show the dropdown menu if it has gained focus when cycling though the input controls (focus traversal). I.e. I don't want the user to press SPACE first as he must make a choice anyway. I have the following code so far:
import java.util.Arrays;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.ChoiceBox;
import javafx.scene.layout.GridPane;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
public class SampleApp extends Application {
public static void main(String[] args) {
launch(args);
}
#Override
public void start(Stage primaryStage) {
StackPane root = new StackPane();
GridPane pane = new GridPane();
ChoiceBox<String> box1 = new ChoiceBox<String>();
box1.getItems().addAll("1", "2", "3");
ChoiceBox<String> box2 = new ChoiceBox<String>();
box2.getItems().addAll("a", "b", "c");
for (ChoiceBox<String> choiceBox : Arrays.asList(box1, box2)) {
choiceBox.focusedProperty().addListener((observable, oldValue, newValue) -> {
if (newValue && !oldValue) {
// transition from unfocused to focused -> expand choicebox
if (!choiceBox.isShowing()) {
choiceBox.show();
}
}
});
}
pane.add(box1, 0, 0);
pane.add(box2, 1, 0);
root.getChildren().add(pane);
primaryStage.setScene(new Scene(root));
primaryStage.show();
}
}
This code works fine when I use the keyboard for focus traversal, but if I click the the (unfocused) ChoiceBox with the mouse, the dropdown shows for a few miliseconds and then hides instantly again. I guess that the ChoiceBox has a predefined EventHandler for mouse events which "toggles" whether the items are shown or not. Apparently, the FocusedProperty is changing first, showing the items, and then the MouseEvents hides them again.
How can I fix this?

Answer 1

Use the consume method of MouseEvents to stop further propagation of the Event through the dispatch chain.
final ChangeListener<? super Boolean> showHideBox = ( __, ___, isFocused ) ->
{
if ( isFocused.booleanValue() )
{
choiceBox.show();
}
else
{
choiceBox.hide();
}
};
choiceBox.focusedProperty().addListener( showHideBox );
choiceBox.addEventFilter( MouseEvent.MOUSE_RELEASED, release ->
{
release.consume();
choiceBox.requestFocus();
} );
Full example : https://gist.github.com/flasheater/0cc365227a235c3fb794 .