Updating a JavaFX status label

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>