How to prevent user pressing multiple keys Javafx? - events

Question

I have a player that can move when pressing the arrow keys. I would like to prevent the user to press multiple arrows at the same time.
This what I have tried:
boolean[] pressedKeys = new boolean[4];
canvas.setOnKeyPressed(event -> {
if (!Arrays.asList(pressedKeys).contains(true)){
if (event.getCode() == KeyCode.UP){
pressedKeys[0] = true;
} else if (event.getCode() == KeyCode.RIGHT){
pressedKeys[1] = true;
} else if (event.getCode() == KeyCode.DOWN){
pressedKeys[2] = true;
} else if (event.getCode() == KeyCode.LEFT){
pressedKeys[3] = true;
}
}
});
canvas.setOnKeyReleased(event -> {
if (event.getCode() == KeyCode.UP){
pressedKeys[0] = false;
} else if (event.getCode() == KeyCode.RIGHT){
pressedKeys[1] = false;
} else if (event.getCode() == KeyCode.DOWN){
pressedKeys[2] = false;
} else if (event.getCode() == KeyCode.LEFT){
pressedKeys[3] = false;
}
});
But it does not work, here I can still press the right and the up arrows for example.
Thanks for any help

Answer 1

I'd create an event handler implementation like this:
class InputHandler implements EventHandler<KeyEvent> {
final private Set<KeyCode> activeKeys = new HashSet<>();
#Override
public void handle(KeyEvent event) {
if (activeKeys.isEmpty() && KeyEvent.KEY_PRESSED.equals(event.getEventType())) {
activeKeys.add(event.getCode());
} else if (KeyEvent.KEY_RELEASED.equals(event.getEventType())) {
activeKeys.remove(event.getCode());
}
}
public Set<KeyCode> getActiveKeys() {
return Collections.unmodifiableSet(activeKeys);
}
}
The check activeKeys.isEmpty() ensures that we don't register a new keypress until a prior key is released.
A single value for the activeKey could be used instead of the activeKeys HashSet, I just adapted this from a prior solution which works in a more general case.
To use it:
InputHandler inputHandler = new InputHandler();
scene.setOnKeyPressed(inputHandler);
scene.setOnKeyReleased(inputHandler);
Then, if it is something like a game where the input is checked on each frame update of an AnimationTimer, in the update method you can check the current active keys for the frame and action them, like this:
private AnimationTimer createGameLoop() {
return new AnimationTimer() {
public void handle(long now) {
update(now, inputHandler.getActiveKeys());
if (isGameOver()) {
this.stop();
}
}
};
I am not sure if your chosen strategy will result in a desirable user experience, you will need to try it out and see how well it works in your application.

Answer 2

I found a solution, thanks to #kleopatra
This is what I made:
boolean pressedKeys = false, releasedKeys = true;
canvas.setOnKeyPressed(event -> {
if (releasedKeys){
// Code goes here
pressedKeys = true;
releasedKeys = false;
}
});
canvas.setOnKeyReleased(event -> {
if (pressedKeys){
pressedKeys = false;
releasedKeys = true;
}
});
Like this, its not possible to press multiple keys at one time