javafx Updating the UI using Platform.runLater


Example

Long-running operations must not be run on the JavaFX application thread, since this prevents JavaFX from updating the UI, resulting in a frozen UI.

Furthermore any change to a Node that is part of a "live" scene graph must happen on the JavaFX application thread. Platform.runLater can be used to execute those updates on the JavaFX application thread.

The following example demonstrates how to update a Text Node repeatedly from a different thread:

import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.Scene;
import javafx.scene.layout.StackPane;
import javafx.scene.text.Text;
import javafx.stage.Stage;

public class CounterApp extends Application {

    private int count = 0;
    private final Text text = new Text(Integer.toString(count));

    private void incrementCount() {
        count++;
        text.setText(Integer.toString(count));
    }

    @Override
    public void start(Stage primaryStage) {
        StackPane root = new StackPane();
        root.getChildren().add(text);

        Scene scene = new Scene(root, 200, 200);

        // longrunning operation runs on different thread
        Thread thread = new Thread(new Runnable() {

            @Override
            public void run() {
                Runnable updater = new Runnable() {

                    @Override
                    public void run() {
                        incrementCount();
                    }
                };

                while (true) {
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException ex) {
                    }

                    // UI update is run on the Application thread
                    Platform.runLater(updater);
                }
            }

        });
        // don't let thread prevent JVM shutdown
        thread.setDaemon(true);
        thread.start();

        primaryStage.setScene(scene);
        primaryStage.show();
    }

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

}