Execute task in background

Question

Hello,
I want to load up to nine panels in a TilePane. For each pane I have to run frist an computation of the content (about 300ms) and second have to build the Panel (about 500ms). What I want is, that there are nine ProgressIndicators which exchanges with every panel after its computation.
I tried it with the Platform.runlater command as well as with a service class. The result was always the same. The ProgressIndicator are shown, but not animated. After seconds there all all panels at once.
Is there a possibility, that the Indicators are animated the hole time and that I can exchange them one after another?
Best Regards,
Tobias Wilker

Answer 1

Thanks for the help. This is how I solved the problem:
import java.util.Random;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.beans.property.SimpleDoubleProperty;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.concurrent.Service;
import javafx.concurrent.Task;
import javafx.concurrent.Worker;
import javafx.concurrent.Worker.State;
import javafx.geometry.Insets;
import javafx.scene.Group;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.ProgressBar;
import javafx.scene.control.ProgressIndicator;
import javafx.scene.layout.StackPane;
import javafx.scene.layout.TilePane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;
public class Minimal extends Application {
     private TilePane loadPane;
     private ProgressIndicator[] indicators = new ProgressIndicator[9];
     private Label loading[] = new Label[9];
     private Color[] colors = {Color.BLACK,Color.BLUE,Color.CRIMSON,Color.DARKCYAN,Color.FORESTGREEN,Color.GOLD,Color.HOTPINK,Color.INDIGO,Color.KHAKI};
     private int counter = 0;
     @Override
     public void start(Stage primaryStage) throws Exception {
          //creating Layout
          final Group root = new Group();                                        
          Scene scene = new Scene(root, 400, 400);               
          primaryStage.setScene(scene);
          primaryStage.setResizable(false);
          StackPane waitingPane = new StackPane();
          final ProgressBar progress = new ProgressBar();
          Label load = new Label("loading things...");
          progress.setTranslateY(-25);
          load.setTranslateY(25);
          waitingPane.getChildren().addAll(new Rectangle(400,400,Color.WHITE),load,progress);
          root.getChildren().add(waitingPane);
          //Task for computing the Panels:
          Task<Void> task = new Task<Void>() {
               @Override
               protected Void call() throws Exception {
                    for (int i = 0; i < 20; i++) {
                    try {
                        Thread.sleep(new Random().nextInt(1000));
                    } catch (InterruptedException ex) {
                        ex.printStackTrace();
                    final double prog = i*0.05;
                    Platform.runLater(new Runnable() {
                        public void run() {
                            progress.setProgress(prog);
                    return null;
          //stateProperty for Task:
          task.stateProperty().addListener(new ChangeListener<Worker.State>() {
               @Override
               public void changed(ObservableValue<? extends State> observable,
                         State oldValue, Worker.State newState) {
                    if(newState==Worker.State.SUCCEEDED){
                         loadPanels(root);
          //start Task
          new Thread(task).start();
          primaryStage.show();
     private void loadPanels(Group root) {
          //change to loadPanel:
          root.getChildren().set(0,createLoadPane());
          //Service:
          final Service<Rectangle> RecBuilder = new Service<Rectangle>() {
                @Override protected Task<Rectangle> createTask() {
                     return new Task<Rectangle>() {
                          @Override protected Rectangle call() throws InterruptedException {
                               updateMessage("loading rectangle . . .");
                              updateProgress(0, 10);
                              for (int i = 0; i < 10; i++) {
                                Thread.sleep(100);
                              updateMessage("Finish!");
                              return new Rectangle((380)/3,(380)/3,colors[counter]);
          //StateListener
          RecBuilder.stateProperty().addListener(new ChangeListener<Worker.State>() {
               @Override public void changed(ObservableValue<? extends Worker.State> observableValue,
                                   Worker.State oldState, Worker.State newState) {
                    switch (newState) {
                    case SCHEDULED:
                         break;
                    case READY:
                    case RUNNING:
                        break;
                    case SUCCEEDED:
                        Rectangle rec = RecBuilder.valueProperty().getValue();
                        indicators[counter].progressProperty().unbind();
                        loading[counter].textProperty().unbind();
                        loadPane.getChildren().set(counter, rec);
                        if(counter<8){
                             counter++;
                             nextPane(RecBuilder);
                        break;
                    case CANCELLED:
                    case FAILED:
                        loading[counter].textProperty().unbind();
                        loading[counter].setText("Failed!");
                        if(counter<8){
                             counter++;
                             nextPane(RecBuilder);
                         break;
          //begin PanelBuilding:
          nextPane(RecBuilder);
     private void nextPane(Service<Rectangle> recBuilder) {
          loading[counter].textProperty().bind(recBuilder.messageProperty());
          indicators[counter].visibleProperty().bind(recBuilder.progressProperty().isNotEqualTo(new SimpleDoubleProperty(ProgressBar.INDETERMINATE_PROGRESS)));
          recBuilder.restart();
     private Node createLoadPane() {
          loadPane = new TilePane(5,5);
          loadPane.setPrefColumns(3);
          loadPane.setPadding(new Insets(5));
          for(int i=0;i<9;i++){
               StackPane waitingPane = new StackPane();
               Rectangle background = new Rectangle((380)/3, (380)/3, Color.WHITE);
               indicators[i] = new ProgressIndicator();
               indicators.setPrefSize(50, 50);
               indicators[i].setMaxSize(50, 50);
               indicators[i].setTranslateY(-25);
               indicators[i].setTranslateX(-10);
               loading[i] = new Label();
               loading[i].setTranslateY(25);
               waitingPane.getChildren().addAll(background,indicators[i],loading[i]);
               loadPane.getChildren().add(waitingPane);
          return loadPane;
     public static void main(String[] args) {
          launch(args);