Trying to set up an "onshowing" ActionEvent in Combobox in javafx - javafx

Question

I'm using Scene Builder to build a javafx gui, and I want a ComboBox where something will happen "On Showing." It looks simple enough, but it crashes when I try to implement it. I created a simple version having nothing but a combobox, and it still crashes.
Here is the Main.java module:
package application;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.layout.BorderPane;
public class Main extends Application {
#Override
public void start(Stage primaryStage) {
try {
// BorderPane root = new BorderPane();
BorderPane root = (BorderPane) FXMLLoader.load(Main.class.getResource("Comboscreen.fxml"));
Scene scene = new Scene(root,400,400);
scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
primaryStage.setScene(scene);
primaryStage.show();
} catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
launch(args);
}
}
Here is the fxml:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.ComboBox?>
<?import javafx.scene.layout.BorderPane?>
<?import javafx.scene.layout.VBox?>
<BorderPane xmlns="http://javafx.com/javafx/8.0.65" xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.Controller">
<center>
<VBox alignment="CENTER" prefHeight="400.0" prefWidth="400.0" BorderPane.alignment="CENTER">
<children>
<ComboBox fx:id="ComboTestBox" onAction="#ComboDo" onShowing="#Showaction" prefWidth="150.0" promptText="Testbox" />
</children>
</VBox>
</center>
</BorderPane>
and here is the Controller:
package application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.ComboBox;
public class Controller {
#FXML
public ComboBox<String> ComboTestBox;
#FXML
void ComboDo(ActionEvent event) {
System.out.println(" Option Chosen");
}
ObservableList<String> options =
FXCollections.observableArrayList(
"Option 1",
"Option 2",
"Option 3"
);
#FXML
void Showaction(ActionEvent event) {
System.out.println(" TestAction");
}
public void initialize() {
ComboTestBox.setItems(options);
}
}
It looks simple enough, but it crashes every time. If I remove the "onshowing" action, it works just fine. Any advice is appreciated, as I am pretty new at this.

Answer 1

Assuming by "crashing" you mean it gives you a runtime exception (for future reference, please include the stack trace, which has lots of information for you to diagnose the problem, in your question):
The onShowing handler is an EventHandler<Event>, not an EventHandler<ActionEvent>, so you need:
#FXML
void Showaction(Event event) {
System.out.println(" TestAction");
}
Note that if you're not using the Event parameter, you can omit it, and the FXMLLoader will still be able to map to the correct handler method:
#FXML
void Showaction() {
System.out.println(" TestAction");
}
However, if you include the parameter, it must be of the correct type.
As an aside, you should use proper naming conventions, i.e.
#FXML
void showAction(Event event) {
System.out.println(" TestAction");
}
with the corresponding change to your FXML file.