Implementation not following documentation regarding when event handler gets called

[Nir Lisker]

Didn't look too deep, but seems like a bug or incorrect doc. I don't see
such specifications in other "setOnX" methods.

On Sun, May 28, 2023 at 1:02 PM John Hendrikx <john.hendrikx at gmail.com>
wrote:

> When looking at the code for Scene#setOnKeyPressed, I noticed that it
> calls Scene#setEventHandler.  This is documented as:
>
>      /**
>       * Sets the handler to use for this event type. There can only be
> one such
>       * handler specified at a time. This handler is guaranteed to be
> called
>       * first. This is used for registering the user-defined onFoo event
>       * handlers.
>       *
>       * @param <T> the specific event class of the handler
>       * @param eventType the event type to associate with the given
> eventHandler
>       * @param eventHandler the handler to register, or null to unregister
>       * @throws NullPointerException if the event type is null
>       */
>      protected final <T extends Event> void setEventHandler(
>              final EventType<T> eventType,
>              final EventHandler<? super T> eventHandler) {
>
> Note that it specifically says "This handler is guaranteed to be called
> first."
>
> This function eventualy calls CompositeEventHandler#setEventHandler.
> This class tracks a chain of handlers, and reserves a special spot for a
> single special "eventHandler".  Yet, in its dispatchBubblingEvent
> method, it clearly calls the "special" handler LAST... see below:
>
>      public void dispatchBubblingEvent(final Event event) {
>          final T specificEvent = (T) event;
>
>          EventProcessorRecord<T> record = firstRecord;
>          while (record != null) {
>              if (record.isDisconnected()) {
>                  remove(record);
>              } else {
>                  record.handleBubblingEvent(specificEvent);
>              }
>              record = record.nextRecord;
>          }
>
>          if (eventHandler != null) {
>              eventHandler.handle(specificEvent);
>          }
>      }
>
> I've confirmed this with this small program (order of calls doesn't make
> a difference):
>
>      public static class App extends Application {
>        @Override
>        public void start(Stage primaryStage) {
>          Button button1 = new Button("111");
>
>          HBox hBox = new HBox();
>          hBox.getChildren().addAll(button1);
>          Scene scene = new Scene(hBox, 300, 300);
>
>          scene.addEventHandler(KeyEvent.KEY_PRESSED, e -> {
>            System.out.println("KeyPressedHandler " + e);
>          });
>          scene.setOnKeyPressed(e -> {
>            System.out.println("Main " + e);
>            e.consume();
>          });
>
>          primaryStage.setScene(scene);
>          primaryStage.show();
>        }
>
> Which outputs the events not in the order documented:
>
> KeyPressedHandler KeyEvent [source = javafx.scene.Scene at 36dbf594, target
> = Button at 5dd3d27e[styleClass=button]'111', eventType = KEY_PRESSED,
> consumed = false, character =  , text = f, code = F]
> Main KeyEvent [source = javafx.scene.Scene at 36dbf594, target =
> Button at 5dd3d27e[styleClass=button]'111', eventType = KEY_PRESSED,
> consumed = false, character =  , text = f, code = F]
>
> --John
>
>
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