Javafx 8 - setVisible() is blocked - javafx-8

Question

So here is my situation:
I have built a GUI using the scene Builder and it works just fine: A search box and a list. When the user search a value the results are correctly displayed on the list.
What I've tried to do is to add a progress bar to be showed when the user makes a search. For that I have added a pane to be used as a wrapper and inside the pane there is the progress bar.
On the controller initialization I do a:
progressBarWrapper.setVisible(false)
which works. When I try to activate it inside the search it doesn't:
private void search() {
progressBarWrapper.setVisible(true);
String val = searchField.getText();
if (val!= null && !"".equals(val)) {
ObjectList list = service.getObjects(val);
objects.clear();
objects.addAll(list);
}
progressBarWrapper.setVisible(false);
}
what I've realized is that if I remove the bottom line where the wrapper is set to invisible again I do get my progress bar to show up, however only when I already have the results.
I guess this is some kind of blocking issue or the redraw process of the screen beeing held back while computations are beeing made, however I don't understand what is going on... can somebody shed a light on it so I can develop it further? Just explain why this behaviour happens so I can have an idea on how to solve it.
Thanks
EDIT: Here I am adding a SSCCE to exemplify
Main.java
package application;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;
public class Main extends Application {
#Override
public void start(Stage primaryStage) {
try {
FXMLLoader loader = new FXMLLoader();
loader.setLocation(Main.class.getResource("Main.fxml"));
Parent root = loader.load();
Scene primaryScene = new Scene(root);
primaryStage.setScene(primaryScene);
primaryStage.setTitle("Test");
primaryStage.show();
} catch (Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
launch(args);
}
}
In the controller I have simulated the getting of data through a simple loop with a thread sleep inside.
MainController.java
package application;
import javafx.fxml.FXML;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.ProgressBar;
import javafx.scene.layout.Pane;
public class MainController {
#FXML
private Button startLoop;
#FXML
private ProgressBar progressBar;
#FXML
private Pane progressBarWrapper;
#FXML
private Label loopCounter;
#FXML
public void initialize() {
System.out.println("Application Started");
progressBarWrapper.setVisible(false);
}
#FXML
private void doLoop() {
progressBarWrapper.setVisible(true);
for (int i = 1; i <= 5; i++) {
progressBar.setProgress(i * 0.2);
loopCounter.setText(String.format("%s loop(s)", i));
try {
Thread.sleep(1000); // 1000 milliseconds is one second.
} catch (InterruptedException ex) {
Thread.currentThread().interrupt();
}
}
progressBarWrapper.setVisible(false);
}
}
And the View:
Main.fxml
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.*?>
<?import javafx.scene.text.*?>
<?import java.lang.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.layout.AnchorPane?>
<AnchorPane prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8.0.40" xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.MainController">
<children>
<Button fx:id="startLoop" layoutX="258.0" layoutY="14.0" mnemonicParsing="false" onAction="#doLoop" prefHeight="80.0" prefWidth="84.0" text="START LOOP" />
<Label fx:id="loopCounter" layoutX="286.0" layoutY="165.0" text="0">
<font>
<Font name="System Bold" size="48.0" />
</font>
</Label>
<Pane fx:id="progressBarWrapper" layoutX="461.0" layoutY="297.0" prefHeight="400.0" prefWidth="600.0" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
<children>
<ProgressBar fx:id="progressBar" layoutX="200.0" layoutY="191.0" prefWidth="200.0" progress="0.0">
<cursor>
<Cursor fx:constant="WAIT" />
</cursor>
</ProgressBar>
</children>
</Pane>
</children>
</AnchorPane>
All is simply under a package called "application"

Answer 1

During some help by the user kleopatra in the comments I came accross the following link from oracle:
https://docs.oracle.com/javafx/2/threads/jfxpub-threads.htm
Basically my problem sums up to the following:
The JavaFX scene graph, which represents the graphical user interface
of a JavaFX application, is not thread-safe and can only be accessed
and modified from the UI thread also known as the JavaFX Application
thread. Implementing long-running tasks on the JavaFX Application
thread inevitably makes an application UI unresponsive. A best
practice is to do these tasks on one or more background threads and
let the JavaFX Application thread process user events.
Hope it helps someone!