How to set Alert box position over current primaryStage? (JavaFX)

Question

EDIT: I have an alert box that pops up if the user clicks "Delete" for removing an item in a ListView. It works, but I would like it to pop over the original stage. It showed up in my first monitor. Is there any way to set the position of the alert when it's shown?

Note, the "owner" is in a different class, and I created everything with Scenebuilder/FXML. I cannot figure out how to get initOwner() to work. Here is the "Main" class:

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class Assignment_5 extends Application {
    public Stage primaryStage;

    @Override
    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("Assignment_5.fxml"));
    primaryStage.setTitle("Plant Pack");
    primaryStage.setScene(new Scene(root, 1200, 500));
    primaryStage.show();
}

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

Here is the working code within the Controller class. It's not necessary to implement the modality of this alert, but it would be a nice addition to make it more convenient. I simply don't know how to pass the main Window from the Main class to this:

    protected void handleDeleteButtonClick(ActionEvent event) {
    Alert alertBox = new Alert(Alert.AlertType.CONFIRMATION, "Confirm Delete", ButtonType.OK, ButtonType.CANCEL);
    alertBox.setContentText("Are you sure you want to delete this " + plantType.getValue().toString().toLowerCase() + "?");
    alertBox.showAndWait();
    if(alertBox.getResult() == ButtonType.OK) {
        int selectedPlant = plantList.getSelectionModel().getSelectedIndex();
        observablePlantList.remove(selectedPlant);
    }
    else {
        alertBox.close();
    }
}

I understand this is fairly new, so it's difficult to find many resources. If anyone knows any info I may have missed, please let me know. Thanks for any help offered. I am using Java 8 with IntelliJ 14.1.5.

Answer 1

As @jewelsea suggests, setting the modality and owner for the alert box will assure that the alert will appear over the stage, even if the stage is moved.

import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.scene.Scene;
import javafx.scene.control.Alert;
import javafx.scene.control.Button;
import javafx.scene.control.ButtonType;
import javafx.scene.control.ListView;
import javafx.scene.layout.BorderPane;
import javafx.stage.Modality;
import javafx.stage.Stage;

public class DeleteAlertDemo extends Application {

    Stage owner;
    ObservableList<String> observablePlantList;
    ListView<String> plantList;

    protected void handleDeleteButtonClick(ActionEvent event) {
        String item = plantList.getSelectionModel().getSelectedItem();
        Alert alertBox = new Alert(Alert.AlertType.CONFIRMATION, "Confirm Delete", 
                ButtonType.OK, ButtonType.CANCEL);
        alertBox.setContentText("Are you sure you want to delete this " 
                + item.toLowerCase() + "?");
        alertBox.initModality(Modality.APPLICATION_MODAL); /* *** */
        alertBox.initOwner(owner);                         /* *** */
        alertBox.showAndWait();
        if (alertBox.getResult() == ButtonType.OK) {
            int selectedPlant = plantList.getSelectionModel().getSelectedIndex();
            observablePlantList.remove(selectedPlant);
        } else {
            alertBox.close();
        }
    }

    @Override
    public void start(Stage primaryStage) {
        owner = primaryStage;                /* *** */
        Button deleteBtn = new Button();
        deleteBtn.setText("Delete");
        deleteBtn.setOnAction(this::handleDeleteButtonClick);

        observablePlantList = FXCollections.observableArrayList("Begonia", 
                "Peony", "Rose", "Lilly", "Chrysanthemum", "Hosta");
        plantList = new ListView<>(observablePlantList);
        plantList.getSelectionModel().select(0);
        BorderPane root = new BorderPane();
        root.setCenter(plantList);
        root.setRight(deleteBtn);

        Scene scene = new Scene(root, 300, 250);

        primaryStage.setTitle("Delete Alert Demo");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        launch(args);
    }

}