How to create a thread in JavaFX that will add a Label until the Stop button is clicked?

Question

Java

How to create a thread in JavaFX that will add a Label until the Stop button is clicked?
if you create something like this, then an error occurs - Not on FX application thread; currentThread = Thread-4

Thread addLabel = new Thread(new Runnable() {
            @Override
            public void run() {
                while(start) {
                    vBox.getChildren().addAll(new Label("new label"));
                }
            }
        });

Answer 1

JavaFX, like many other gui libraries, is single-threaded. When a window is created, an Event Dispatch Thread is created , inside which the event loop and event handlers will work. You should not attempt to interact with GUI elements from the main thread or any other thread - this will crash. You should not start threads inside event handlers - this will lead to a crash. If you need to change, for example, the label text from another thread, you will have to create a task for the EDT:
If you need to launch a long-running task inside a button click handler, you will have to use Task and Service :

public class Example extends Application {
    ...

    btn.setOnAction(act -> {
        Service<Void> service = new Service<Void>() {
            @Override
            protected Task<Void> createTask() {
                return new Task<Void>() {
                    @Override
                    protected Void call() throws Exception {
                        // Долгий код
                        return null;
                    }
                };
            }
        };
        service.start();
    });
}

Note

На самом деле поток обработки событий в JavaFX называется JavaFX Application Thread, но это непринципиально.

Answer 2

here it is better to use the reverse strategy.
we create a thread that thinks for a long time, and from it we somehow inform the gui thread so that it already creates a label.

Answer 3

I personally use either AnimationTimer or Platform.runLater to change UI from JavaFx thread
but mostly AnimationTimer

boolean update=false;
        AnimationTimer animationTimer=new AnimationTimer() {
            @Override
            public void handle(long now) {
                // от здесь уже процесс от JavaFx,  можешь спокойно обновлять UI
                if(update){
                    update=false;
                    // обычно у меня так выглядет
                    // TODO обновление UI
                }
            }
        };
        animationTimer.start();

for some reason, I have not used runLater anywhere yet, but I tried

Platform.runLater(new Runnable() {
            @Override
            public void run() {
                //  здесь уже поток от JavaFx
            }
        });

there are a couple more ways related to something like Task, but I haven’t tried it, because of the complexity