JavaFX block MouseEvent until delayedExecutor finishes its job - javafx

Question

I'm trying to create a simple memory match game using Java 11 and JavaFX.
I have a scenario where two cards don't match. Before the non-matching cards are flipped back I'd like to have 800 milliseconds delay, so the user can see what was the second selected card. I'm using this code and it works fine:
CompletableFuture.delayedExecutor(800, TimeUnit.MILLISECONDS).execute(() -> {
firstRevealedCard.setFaceDown(); // sets an ImageView's setImage() method
secondRevealedCard.setFaceDown(); // sets an ImageView's setImage() method
firstRevealedCard = null; // sets instance variable to null
secondRevealedCcard = null; // sets instance variable to null
});
All the cards in the game are in a 4 column and 2 row GridPane.
Each cell in the grid is an ImageView set to an Image.
Each card object has a Mouse (click) event attached to it:
// Add all cards to the deck
for ( int card_ID = 1; card_ID < unique_cards+1; card_ID++ ) {
Card card1 = new Card( card_ID );
card1.setOnMouseClicked( (MouseEvent event) -> { onMouseClicked(card1); });
addCard(card1);
Card card2 = new Card( card_ID );
card2.setOnMouseClicked( (MouseEvent event) -> { onMouseClicked(card2); });
addCard( card2 );
In the code above card1 and card2 are two cards having the same picture. They're matching cards.
The cards are stored in an ArrayList. After all the cards has been added to the ArrayList, the ArrayList is shuffled.
The ArrayList store Card objects and each object has its own mouse event listener attached.
THE ISSUE: When two cards don't match, the non-matching cards need to flip back and the 800 milliseconds timeout works well using the CompletableFuture.delayedExecutor, but I want the "mouse event" to be blocked or locked until the Executor fininshes, otherwise, let's say the user clicks an other card, but the non-matching cards didn't have the chance to flip back.
First card selected - Apple
Second card selected - Banana
Two non-matching cards
Executor starts
100 milliseconds
100 milliseconds
100 milliseconds
100 milliseconds
the user clicks another card (throws an exception)
just because user clicked another card before executor finishes
100 millisecond
...
...
at 800 milliseconds
Executor finishes, cards are flipped back
Exception in thread "ForkJoinPool.commonPool-worker-3" java.lang.NullPointerException
at memorygamefx.CardDeck.lambda$onMouseClicked$0(CardDeck.java:85)
at java.base/java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1426)
at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1020)
at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)
at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)
at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:177)
I would be grateful for any suggestion. Thank you!

Answer 1

Don't use delayedExecutor for this. If you continue to do so, wrap the delayed code you invoke in Platform.runLater, so that it runs on the JavaFX thread otherwise weird stuff might happen.
Instead use a PauseTransition such as this:
PauseTransiton pause = new PauseTransition(Duration.millis(800));
Node disabledNode = scene.getRoot();
disabledNode.setDisable(true);
pause.setOnFinished(e -> {
disabledNode.setDisable(false);
// delayed code that you would like to run.
});
pause.play();
The example disables the entire scene when the pause is executing.
A binding can also be used instead, but manually setting and unsetting the disable property is probably better:
scene.getRoot().disableProperty().bind(
Bindings.equal(pause.statusProperty(), Animation.Status.RUNNING)
);
Disabling the scene will, by default, grey it out to give feedback that it is disabled. If you don't want that, you could instead add or remove a mouse event filter (please read attached link to understand this if you don't know what it is) on a scene or a hierarchy or nodes to prevent input that you don't want the app to process during the pause.
Another thing you could do to disable mouse input, is to set the root node to mouseTransparent while the pause is running, that way mouse input will be ignored. That would be similar to defining your own filters to ignore mouse events, but much easier to implement.
Some advantage of a PauseTransition are:
Everything runs on the JavaFX thread, so you don't need to deal with multi-threading issues.
It has a rich API so it is quite flexible.
It is reusable.