JavaFX从另一个线程更新UI

Question

I have a main class

    public class Main {
        public static void main(String[] args) {
            Application.launch(View.class);
            View view = new View();
            Platform.runLater(() -> view.changeTitle());
        }
    }

and a view JavaFX class

    public class View extends Application {

        Stage primaryStage;

        public View() {

        }

        @Override
        public void start(Stage primaryStage) throws Exception{
            Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
            primaryStage.setTitle("Hello World");
            primaryStage.setScene(new Scene(root, 300, 275));
            this.primaryStage = primaryStage;
            primaryStage.show();
        }

        public void changeTitle() {
           primaryStage.setTitle("YEA!");
       }
    }

I want the main class to do something in JavaFX thread but my code doesn't work. In documentation said that I can call Platform.runLater() from any thread I want. If I call Platform.runLater() from JavaFX thread (in start(), for example), everything is OK.

Answer 1

First, main(String) is blocked on Application.launch(Class) .

From Oracle Javadocs:

The launch method does not return until the application has exited, either via a call to Platform.exit or all of the application windows have been closed.

Second, you're creating a new View instance on the second line. That will NOT be same instance Application created, so your Platform.runLater wouldn't affect the launched application even if that code were reachable before it exited.