Populate TreeView and display status messages

Question

I'm trying to populate my TreeView and update the text of status label before and after the populating.

my code looks something like this:

public void populateTreeView() {
    // start message
    this.label.setText("Process started...");

    // populate the TreeView, this takes several minutes

    // finish message
    this.label.setText("Done!");
}

It's not working as I expected. I tried put each of the the 3 main sections of this method in Platform.runLater() and that didn't work, too. The app just freezes for some seconds and then I see the populated TreeView and the "Done" text.

How can I get this behavior?

Thanks in advance

You should populate the TreeView in a background thread. [Check this post](https://stackoverflow.com/a/30250308/1759128) on how to correctly write JavaFX program for long running tasks. — ItachiUchiha, Aug 26 '18 at 10:43

score 1 · Accepted Answer · answered Aug 26 '18 at 17:32

You will need to execute the loading method in a background Thread. Basically, the interface that you create and all of its events are executed on the JavaFX Application Thread (JFXAT).

These events are generally executed one at a time, so if you run a long process on this Thread, the UI will appear to be frozen until that process is completed.

While there are several ways to create background tasks in JavaFX, below is a simple demo application that uses a Task to do so.

The example code is commented throughout to explain what we are doing. The example uses a ListView instead of a TreeView, just for simplicity, but the concept is the same regardless.

This example shows a basic interface with a ListView and a Button to start the loading process. At the bottom is a Label that will keep the user updated on the current step in the Task's process.

import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.concurrent.Task;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.ListView;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

import java.util.ArrayList;
import java.util.List;

public class Main extends Application {

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

    @Override
    public void start(Stage primaryStage) {

        // Just a simple interface
        VBox root = new VBox(5);
        root.setPadding(new Insets(10));
        root.setAlignment(Pos.CENTER);

        // Create the list view
        ListView<String> listView = new ListView<>();
        listView.setPrefHeight(200);

        // Status label
        Label lblStatus = new Label();

        // Here we will create a new Task that will run in the background
        Task<List<String>> loadDataTask = new Task<List<String>>() {

            // We override the call() method; this is the code that is run when the task is started. When the Task
            // is completed, it will return a new List of Strings
            @Override
            protected List<String> call() throws Exception {

                // Tasks have a messageProperty that allows us to keep the UI informed. We will bind this value to
                // our Label later
                updateMessage("Loading data ...");

                // Generate some sample data
                List<String> listOfItems = new ArrayList<>();
                listOfItems.add("One");
                listOfItems.add("Two");
                listOfItems.add("Three");
                listOfItems.add("Four");
                listOfItems.add("Five");

                // Simulate a long-running task by pausing the thread for 10 seconds
                Thread.sleep(10000);

                // Now we can update the messageProperty again and return the completed data List
                updateMessage("Finished!");

                return listOfItems;
            }
        };

        // We can now tell our application what to do once the Task has finished (either successfully or failure)
        loadDataTask.setOnFailed(wse -> {
            // This is called if an exception is thrown during the execution of the Task
            // We will just print the Exception in this sample
            loadDataTask.getException().printStackTrace();
        });

        // The Task completed successfully so lets now bind the List to our ListView
        loadDataTask.setOnSucceeded(wse -> {
            listView.setItems(FXCollections.observableArrayList(loadDataTask.getValue()));
        });

        // Now that we've defined our background Task and what to do when it's completed, let's create a button
        // that allows us to start the task.
        Button button = new Button("Load Data");
        button.setOnAction(e -> {

            // Let's bind our Label to the Task's messageProperty. This will cause the Label to update automatically
            // whenever the Task calls the updateMessage() method.
            lblStatus.textProperty().bind(loadDataTask.messageProperty());

            // Now let's start the Task on a background Thread. This will cause the rest of the UI to remain
            // responsive.
            new Thread(loadDataTask).start();
        });

        // Add the controles to the Scene
        root.getChildren().addAll(
                button,
                listView,
                new Label("Status:"),
                lblStatus);

        primaryStage.setScene(new Scene(root));

        primaryStage.show();
    }
}

When the button is clicked, the background Task is executed, the Label is updated to show "Loading data ..." and the long-running task begins.

When the Task finishes, the ListView gets updated with the data and the Label will show `Finished!"

Thank you so much for the detailed explanation! It was very helpful! — Ori Netanel Ben-Zaken, Aug 28 '18 at 07:06

Populate TreeView and display status messages

1 Answers1