JavaFX - How to change view in method body

Question

I'm trying to write a code that will simulate sand pile, and I would like to open new window with simulation in another thread. In this case I have to dynamically change view of the 2nd window, but the view waits until the simulate() method ends even if it is run in another thread. What can I do to change view in SandPileApplicationSimulation:run() method body?

Controller class - simulation method:

public class SandPileController {

    @FXML
    public TextField interval;

    @FXML
    public TextField pathToBoard;

    @FXML
    public ChoiceBox<String> sandGenerationMode;

    @FXML
    protected void simulate() {

// you can ignore that 3 lines
        FieldRoleFileParser parser = new FieldRoleFileParser();
        FieldRole[][] fieldRoles = parser.parse(pathToBoard.getText());

        String value = sandGenerationMode.getValue();
       // this construtor is running initializeView method and it is creating new Stage
        SandPileApplicationSimulation sandPileApplicationSimulation = new SandPileApplicationSimulation(fieldRoles,
                Double.parseDouble(interval.getText()),
                SandGenerationMode.valueOf(value));
        Thread thread = new Thread(sandPileApplicationSimulation);
        thread.start();
    }
}

Stage view:

private void initializeView(FieldRole[][] values) {
        Stage stage = new Stage();

        GridPane root = new GridPane();

       //this loops generates some rectangles based on input
        for (int i = 0; i < columnCount; i++) {
            for (int j = 0; j < columnLength; j++) {
                FieldRole fieldRole = values[i][j];
                Rectangle square = new Rectangle(50, 50);
                square.setFill(fieldRole.getColor());
                root.add(square, i, j);
                board[i][j] = new Field(fieldRole, square);
            }
        }

        stage.setScene(new Scene(root));
        stage.show();
    }

run() method (from Runnable) in SandPileApplicationSimulation class - the method wherein I would like to change the view of scene:

@Override
    @SneakyThrows
    public void run() {

        boolean simulationMode = true;
        boolean hasAnyChange = true;

        generateSand(); // <-- this method change the color of some rectangles


        while (hasAnyChange) {

            hasAnyChange = false;

            Thread.sleep(interval);
            hasAnyChange = simulateFrame(simulationMode); // <-- this lane should change the view by changing the color of rectangles 

            simulationMode = !simulationMode;
            generateSand();
        }

    }

I tried to write only the important information; if I forget something, just tell me please. Thanks for your answers.

EDIT: Here is also main application class and fxml file (only main app has it) class:

@Override
    public void start(Stage stage) throws IOException {
        FXMLLoader fxmlLoader = new FXMLLoader(SandPileApplication.class.getResource("view.fxml"));
        Scene scene = new Scene(fxmlLoader.load(), 320, 175);
        stage.setTitle("Sand pile simulation");
        stage.resizableProperty()
                .setValue(false);
        stage.setScene(scene);
        stage.show();
    }

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

fxml

<VBox alignment="CENTER" spacing="20.0" xmlns:fx="http://javafx.com/fxml"
      fx:controller="pl.umcs.sandpilesimulator.SandPileController">
    <padding>
        <Insets bottom="20.0" left="20.0" right="20.0" top="20.0"/>
    </padding>

    <TextField fx:id="interval">1.0</TextField>
    <TextField fx:id="pathToBoard" promptText="Path to file with board..."/>
    <ChoiceBox fx:id="sandGenerationMode">
        <items>
            <FXCollections fx:factory="observableArrayList">
                <String fx:value="CENTER" />
                <String fx:value="RANDOM" />
            </FXCollections>
        </items>
    </ChoiceBox>
    <Button text="Simulate" onAction="#simulate"/>
</VBox>

Answer 1

Everything was working well by javaFx side, but runnable object was running in the same thread for my mistake and I fixed this (code is edited).

Answer 2

This may help. It opens another window to display the ongoing simulation (https://en.wikipedia.org/wiki/Conway%27s_Game_of_Life):

import java.nio.IntBuffer;
import java.util.Random;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.event.ActionEvent;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.ToggleButton;
import javafx.scene.control.ToggleGroup;
import javafx.scene.image.ImageView;
import javafx.scene.image.PixelFormat;
import javafx.scene.image.WritableImage;
import javafx.scene.image.WritablePixelFormat;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
import javafx.stage.StageStyle;


public class MultiWindowDynamic extends Application {

    private static WritablePixelFormat<IntBuffer> pixFmt = PixelFormat.getIntArgbInstance();
    private int width = 200;
    private int height = 200;
    private ToggleButton startButton;
    private ToggleButton stopButton;
    private WritableImage simImage;
    private int [] pixelBuffer;
    private int [] nextBuffer;
    private Thread thread;
    private Stage simWindow;

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

    @Override
    public void start(Stage primaryStage) throws Exception {
        startButton = new ToggleButton("Start");
        stopButton = new ToggleButton("Stop");
        startButton.disableProperty().bind(startButton.selectedProperty());
        stopButton.disableProperty().bind(stopButton.selectedProperty());
        ToggleGroup group = new ToggleGroup();
        group.getToggles().addAll(startButton, stopButton);
        stopButton.setSelected(true);
        startButton.setOnAction(this::startSimulation);
        stopButton.setOnAction(this::stopSimulation);
        HBox buttons = new HBox(16, startButton, stopButton);
        buttons.setAlignment(Pos.CENTER);
        VBox root = new VBox(8, new Label("Press the button to start the simulation."), buttons);
        root.setPadding(new Insets(20));
        Scene scene = new Scene(root);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    private void startSimulation(ActionEvent event) {
        if (simWindow == null) {
            nextBuffer = new int[width * height];
            simImage = new WritableImage(width, height);
            ImageView simImageView = new ImageView(simImage);
            Scene scene = new Scene(new Group(simImageView));
            scene.setFill(Color.BLACK);
            simWindow = new Stage(StageStyle.DECORATED);
            simWindow.setScene(scene);
        }
        simWindow.show();
        Random rng = new Random(System.currentTimeMillis());
        pixelBuffer = rng.ints(width * height, -1, 1).toArray();
        simImage.getPixelWriter().setPixels(0, 0, width, height, pixFmt, pixelBuffer, 0, width);
        thread = new Thread(this::simulationThread);
        thread.setDaemon(true);
        thread.start();
    }

    private void stopSimulation(ActionEvent event) {
        thread.interrupt();
    }

    private void simulationThread() {
        int [] buffer = calculateImage();
        try {
            while (!Thread.interrupted()) {
                nextBuffer = pixelBuffer;
                pixelBuffer = buffer;
                Platform.runLater(() -> {
                    simImage.getPixelWriter().setPixels(0, 0, width, height, pixFmt, pixelBuffer, 0, width);
                });
                buffer = calculateImage();
                Thread.sleep(100);
            }
        } catch (InterruptedException ex) {}
    }

    private int [] calculateImage() {
        for (int p = 0; p < nextBuffer.length; p++) {
            int count = countNeighbours(p);
            if (count == 3) { // birth/survive
                nextBuffer[p] = 0xffffffff;
            } else if (count < 2 || count > 3) { // death
                nextBuffer[p] = 0;
            } else { // stay
                nextBuffer[p] = pixelBuffer[p];
            }
        }
        return nextBuffer;
    }

    private int countNeighbours(int p) {
        return getPixel(p-width-1)
             + getPixel(p-width)
             + getPixel(p-width+1)
             + getPixel(p-1)
             + getPixel(p+1)
             + getPixel(p+width-1)
             + getPixel(p+width)
             + getPixel(p+width+1);
    }

    // returns 1 for a 'set' pixel, and 0 for 'blank'
    // takes advantage of white pixel int being -1;
    private int getPixel(int p) {
        if (p < 0) {
            p += pixelBuffer.length;
        } else if (p >= pixelBuffer.length) {
            p -= pixelBuffer.length;
        }
        return -pixelBuffer[p];
    }

}