[SOLVED] How to wait for user input on JavaFX application thread without using showAndWait?

How to wait for user input on JavaFX application thread without using showAndWait?

I'd like to pause the execution of a method on the JavaFX application thread and wait until the user does interaction with the UI. It's important not to freeze the UI.

Example:

Button start = ...
Button resume = ...

start.setOnAction(evt -> {
     System.out.println("starting");
     start.setDisable(true);
     System.out.println("please press resume button.");
     pause();
     System.out.println("done");
     start.setDisable(false);
});

resume.setOnAction(evt -> resume());

How should I implement the pause() and resume() methods?
The execution of the event handler should wait at pause(); call until the user presses the resume button and the resume method is called.

Solution

You can do so by using Platform.enterNestedEventLoop to pause the execution of the event handler and Platform.exitNestedEventLoop (available since JavaFX 9) to resume the execution:

private final Object PAUSE_KEY = new Object();

private void pause() {
    Platform.enterNestedEventLoop(PAUSE_KEY);
}

private void resume() {
    Platform.exitNestedEventLoop(PAUSE_KEY, null);
}

Platform.enterNestedEventLoop returns when Platform.exitNestedEventLoop is called with the same parameter passed as first argument.