GUI update with threads error

Question

I make board game in javafx and I stumbled upon a problem. My application has Client/Server connection. Whenever server sends data about where player moved his pawn I call a fun

Answer 1

One of your other classes seems to start a thread, which is not controlled by your fx application thread. Hard to tell, which one without seeing the other classes.

Please have a look at what to consider when using background threads in a java fx application (or when using libaries, that do so), e.g. how to use Task and Platform.runLater(Runnable r). There are countless other questions about that topic on SO, that might help you.

https://docs.oracle.com/javase/8/javafx/interoperability-tutorial/concurrency.htm

Answer 2

Clearly Client.run() is being executed on a background thread, and calls Controller.movePawn(), which (via refresh()) updates the UI. You cannot update the UI on a background thread. You need to wrap the code that updates the UI in Platform.runLater(). So, it's pretty hard to tell without a complete example, but using that particular sequence of method calls as an example, it looks like you need to do

public void movePawn(int x1, int y1, int x2, int y2) {
    Platform.runLater(() -> {
        Pawn pawnTemp = game.getBoard().getField(x1, y1).getPawn();
        game.getBoard().getField(x1, y1).setPawn(null);
        game.getBoard().getField(x2, y2).setPawn(pawnTemp);

        refresh();
    });
}

There are probably similar issues throughout the code, but the bottom line is that you:

1. Must execute code that updates the UI on the FX Application Thread
2. Must not execute code that blocks (or takes an appreciable amount of time to run) on the FX Application Thread.