Run logic after window is shown - javafx

Question

I have a small program which gets called by another program, downloads/renames some files and closes itself afterwards. I want to show the user the progress with some simple text. My problem is, that the logic of the code runs before the view is completely shown. The window is visible but the content (in this case the sample text) is not.
I have already tried setOnShown() (as seen in my example) or setOnShowning(). I also tried not using a fxml file for the layout. But nothing seems to work.
public void start(Stage primaryStage) throws Exception {
HBox root = new HBox();
Text t = new Text();
t.setText("sample Text");
root.getChildren().add(t);
Scene scene = new Scene(root, 300, 275);
primaryStage.setTitle("FXML Welcome");
primaryStage.setScene(scene);
primaryStage.setOnShown(e -> {
updaterLogic(); //do some work
});
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
public void updaterLogic(){
try {
Thread.sleep(10 * 1000);
} catch (Exception e) {
e.printStackTrace();
}
}
I want the view to be completed before running the actual logic. How can i archieve this?

Answer 1

To execute something after a window has been shown you can:
Listen for a WindowEvent.WINDOW_SHOWN event.
See Window.onShown and Window.addEventHandler
Listen to the Window.showing property and react when it changes to true.
Put the code after the call to show().
But not showAndWait() as that method doesn't return until the window is closed (and is illegal to call on the primary stage).
However, how to do this is not your problem (you're already using onShown). Your problem is caused by how you execute the "updater logic". Inside your updaterLogic() method you are calling Thread.sleep (simulating work). Since event handlers are executed on the JavaFX Application Thread that causes said thread to block. While the FX thread is blocked it can't do anything related to the GUI (e.g. layout passes, trigger rendering pulses, process user events, etc...)—thus the frozen window with no content rendered.
Move the "updater logic" onto a background thread so that the FX thread remains free to do its work. For general information about concurrency in Java, see Lesson: Concurrency and the java.util.concurrent package. For JavaFX specifics, see Concurrency in JavaFX, the javafx.concurrent package, and Platform.runLater(Runnable).
Here are two golden rules of JavaFX:
You must never block, nor execute long running work on, the JavaFX Application Thread.
You must always access and modify a live scene graph on the JavaFX Application Thread.
This is documented by Node:
Node objects may be constructed and modified on any thread as long they are not yet attached to a Scene in a Window that is showing. An application must attach nodes to such a Scene or modify them on the JavaFX Application Thread.
Note: Some nodes, such as WebView, must be created on the FX thread; this will be documented as appropriate.