Supposedly I have an extended application class to launch from another class

public class BasicApp extends Application {
    public static CountDownLatch instanceLatch = new CountDownLatch(1);
    public static BasicApp instance;

    public synchronized static BasicApp getInstance() {
        if(instance == null) {
            try {
                new Thread(() -> Application.launch(BasicApp.class)).start();
                instanceLatch.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        return instance;
    }

    public BasicApp () {
        instance = this;
        instanceLatch.countDown();
    }
.
.
.

And I want to create multiple instances of the same stage from another class, so I might create a list of stage

    private static List<Stage> stages;

    @Override
    public void start(Stage primaryStage) throws Exception {
        for (Stage st : stages) {
            st.show();
        }
    }
.
.
.

so I define a static method to instantiate the stage from another class

    public static Stage createStage(String data) {
        Stage stage = new Stage();
        Scene scene = new Scene(new Label(data));
        stage.setScene(scene);

        stages.add(stage);

        return stage;
    }
}

However, when I tried to launch the class and create the stage,

public class MainClass {
    public static void main (String[] args) {
        BasicApp app = getInstance();
        app.createStage("Test");
    }
}

It threw an exception that says Stage cannot be created outside the FX Application thread. java.lang.IllegalStateException: Not on FX application thread;

The app instance has no problem, yet, How do I achieve to create the instance of the same stage without getting this error?

CodePudding user response：

You can use Platform.runLater() to execute code on the FX application thread.

public class MainClass {
    public static void main (String[] args) {
        BasicApp app = getInstance();
        Platform.runLater(() -> createStage("Test"));
    }
}