Updating a JavaFX status label - javafx

Question

I have a JavaFX program using Model/View/Controller where I want a long running model to update a status label on the view. I found people suggesting using the Timeline class to do this. I implemented it expecting that every second, the status Label would update. However, only the final status displays. What am I doing wrong?
My controller looks like:
#FXML
private Button pullApplicantsButton;
#FXML
private Label statusLabel;
#FXML
private DatePicker orientationDate;
#FXML
private Spinner numberOfApplicants;
#FXML
private void pullApplicants() throws Exception {
SelectApplicantsModel selectApplicantsModel = new SelectApplicantsModel(orientationDate.getValue() , ( int ) numberOfApplicants.getValue() , this.statusLabel);
selectApplicantsModel.process();
}
my model looks like:
public SelectApplicantsModel(LocalDate nextOrientationDate, int numberOfApplicants , Label statusLabel ) throws FileNotFoundException {
this.nextOrientationDate = nextOrientationDate;
this.numberOfApplicants = numberOfApplicants;
this.statusLabel = statusLabel;
}
public void process() throws Exception {
Timeline timeline = new Timeline(
new KeyFrame(Duration.seconds( 1 ) , event -> {
statusLabel.setText( programStatus );
})
);
timeline.setCycleCount( Animation.INDEFINITE );
timeline.play();
programStatus = "starting";
changeSearchStringToIncludeOrientationDate(nextOrientationDate);
MemberClicks memberClicks = new MemberClicks();
programStatus = "retrieving profiles";
JsonArray applicantProfilesJsonArray = memberClicks.getProfiles(searchJsonArray);
programStatus = "converting profiles";
and the view looks like:
<Label text="Picks the next 30 applicants for the upcoming orientation. Applicants whose Memberclick's OrientationDate matches the next orientation date get priority, followed by those with the oldest normalized application date." wrapText="true" GridPane.columnIndex="0" GridPane.columnSpan="2" GridPane.rowIndex="0" />
<Label text="Date of next orientation:" GridPane.columnIndex="0" GridPane.rowIndex="1" />
<DatePicker fx:id="orientationDate" editable="false" GridPane.columnIndex="1" GridPane.rowIndex="1" />
<Label text="Number of applicants to pull:" GridPane.columnIndex="0" GridPane.rowIndex="2" />
<Spinner fx:id="numberOfApplicants" editable="false" GridPane.columnIndex="1" GridPane.rowIndex="2" />
<Button fx:id="pullApplicantsButton" mnemonicParsing="false" onAction="#pullApplicants" text="Pull Applicants" GridPane.columnIndex="0" GridPane.rowIndex="4" />
<Button fx:id="closeWindowButton" mnemonicParsing="false" onAction="#closeWindow" text="Close Window" GridPane.columnIndex="1" GridPane.rowIndex="4" />
<Label fx:id="statusLabel" text="" wrapText="true" GridPane.columnIndex="0" GridPane.columnSpan="2" GridPane.rowIndex="5" />

Answer 1

You can use a Task for your purpose which does all the work in a background thread so that the GUI thread will not be blocked. Here is a minimal example:
Controller Class:
package sample;
import javafx.fxml.FXML;
import javafx.scene.control.Label;
public class Controller {
#FXML
private Label statusLabel;
#FXML
public void handleStartBtnClick() {
MyTask myTask = new MyTask();
statusLabel.textProperty().bind(myTask.messageProperty());
new Thread(myTask).start();
}
}
MyTask Class:
package sample;
import javafx.concurrent.Task;
public class MyTask extends Task<Void> {
#Override
protected Void call() throws Exception {
updateMessage("starting");
// while (...) {
// do something:
// changeSearchStringToIncludeOrientationDate(nextOrientationDate);
// MemberClicks memberClicks = new MemberClicks();
Thread.sleep(1000); // just for demonstration purpose
// Update the status:
updateMessage("retrieving profiles");
Thread.sleep(1000);
// Do next step:
// ...
updateMessage("converting profiles");
Thread.sleep(1000);
// } End of while loop
return null;
}
#Override
protected void succeeded() {
updateMessage("succeeded");
}
}
FXML File:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.layout.VBox?>
<VBox xmlns="http://javafx.com/javafx/11.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
<children>
<Button onAction="#handleStartBtnClick" text="Start background task"/>
<Label fx:id="statusLabel" text="Status"/>
</children>
</VBox>