Javafx add a dropdown event listener for choicebox

Question

I have a ChoiceBox and I want to refresh it's content whenever user expands it. I haven't found a proper listener for this. All the stuff google gives is related to handling ChangeValue events.

I reckon I should add eventListener<ActionEvent> to ChoiceBox since what I'm handling is click on a ChoiceBox, but my implementation doesn't work.

ActionEvent fires when I click on any List value, not when I click ChoiceBox itself.

Answer 1

Register a listener with the choice box's showingProperty:

choiceBox.showingProperty().addListener((obs, wasShowing, isNowShowing) -> {
    if (isNowShowing) {
        // choice box popup is now displayed
    } else {
        // choice box popup is now hidden
    }
});

Here is a quick demo:

import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.ChoiceBox;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;

public class ChoiceBoxPopupTest extends Application {


    private int nextValue ;

    @Override
    public void start(Stage primaryStage) {
        ChoiceBox<Integer> choiceBox = new ChoiceBox<>();
        choiceBox.getItems().add(nextValue);
        choiceBox.setValue(nextValue);
        choiceBox.showingProperty().addListener((obs, wasShowing, isNowShowing) -> {
            if (isNowShowing) {
                choiceBox.getItems().setAll(++nextValue, ++nextValue, ++nextValue);
            }
        });
        BorderPane root = new BorderPane();
        root.setTop(choiceBox);
        BorderPane.setAlignment(choiceBox, Pos.CENTER);
        root.setPadding(new Insets(5));
        Scene scene = new Scene(root, 400, 400);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

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