How to properly close an alert box javafx - javafx

Question

I am trying to create an alert box type window that is like a user registration panel. Now when I close the window using the top-right button (I do not have a cancel/close button implemented) and re-open it there's this error that pops up:
Caused by: java.lang.IllegalStateException: Cannot set modality once stage has been set visible
at javafx.stage.Stage.initModality(Stage.java:525)
at elibraryserver.NewStudentController.initRegister(NewStudentController.java:150)
at elibraryserver.serverController.addStudentButtonAction(serverController.java:71)
... 53 more
I do not understand since I closed the window shouldn't it reset and open another one? What I can see from the error is that it thinks the window is still open. Or am I wrong?
Here is the code for the stage:
public void initRegister() throws IOException {
FXMLLoader loader = new FXMLLoader();
loader.setLocation(getClass().getResource("newStudent.fxml"));
Parent root = loader.load();
Rectangle2D screenBounds = Screen.getPrimary().getVisualBounds();
registerStage.setX((screenBounds.getWidth() - registerStage.getWidth()) / 2);
registerStage.setY((screenBounds.getHeight() - registerStage.getHeight()) / 2);
Scene scene = new Scene(root);
registerStage.setScene(scene);
registerStage.setTitle("Register Student");
registerStage.initModality(Modality.APPLICATION_MODAL);
registerStage.showAndWait();
}
public void addStudentButtonAction(ActionEvent event) throws IOException {
NewStudentController nsc = new NewStudentController();
nsc.initRegister();
}

Answer 1

Not sure what exactly your issue is I think it is because you are not creating a new stage when you initialize your new window
Here is some example code
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.VBox;
import javafx.stage.Modality;
import javafx.stage.Stage;
import java.io.IOException;
public class Main extends Application {
#Override
public void start(Stage primaryStage) {
Button button = new Button("Open Test window");
VBox vbox = new VBox();
vbox.getChildren().addAll(button);
Scene scene = new Scene(vbox);
Stage stage = new Stage();
stage.setScene(scene);
stage.show();
button.setOnAction(event -> {
try {
openAction();
} catch (IOException e) {
e.printStackTrace();
}
});
}
private void openAction() throws IOException {
FXMLLoader loader = new FXMLLoader();
loader.setLocation(getClass().getResource("Test.fxml"));
Parent root = loader.load();
Stage stage = new Stage();
Scene scene = new Scene(root);
stage.setScene(scene);
stage.setTitle("Register Student");
stage.initModality(Modality.APPLICATION_MODAL);
stage.show();
}
public static void main(String[] args) { launch(args); }
}
testFXML Controller
import javafx.fxml.Initializable;
import javafx.geometry.Insets;
import javafx.scene.control.ColorPicker;
import javafx.scene.layout.*;
import javafx.scene.paint.Paint;
import java.net.URL;
import java.util.ResourceBundle;
public class TestFXMLController implements Initializable{
public ColorPicker colorPicker;
public VBox vBox;
#Override
public void initialize(URL location, ResourceBundle resources) {
colorPicker.setOnAction(event -> {
Paint fill = colorPicker.getValue();
BackgroundFill backgroundFill =
new BackgroundFill(fill,
CornerRadii.EMPTY,
Insets.EMPTY);
Background background = new Background(backgroundFill);
vBox.setBackground(background);
});
}
}
Test.fxml
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.ColorPicker?>
<?import javafx.scene.layout.VBox?>
<VBox fx:id="vBox" alignment="CENTER" prefHeight="300.0" prefWidth="300.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="TestFXMLController">
<children>
<ColorPicker fx:id="colorPicker" opacity="0.5" VBox.vgrow="ALWAYS" />
</children>
</VBox>