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List: openjdk-openjfx-dev
Subject: Re: Implementation not following documentation regarding when event handler gets called
From: Nir Lisker <nlisker () gmail ! com>
Date: 2023-05-29 20:34:35
Message-ID: CA+0ynh_CA3BvAazrPzwbOukQNcTny=dWcA-9TkwEsrEqVLmjyA () mail ! gmail ! com
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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@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@36dbf594, target
> = Button@5dd3d27e[styleClass=button]'111', eventType = KEY_PRESSED,
> consumed = false, character = , text = f, code = F]
> Main KeyEvent [source = javafx.scene.Scene@36dbf594, target =
> Button@5dd3d27e[styleClass=button]'111', eventType = KEY_PRESSED,
> consumed = false, character = , text = f, code = F]
>
> --John
>
>
[Attachment #3 (text/html)]
<div dir="ltr">Didn't look too deep, but seems like a bug or incorrect doc. I \
don't see such specifications in other "setOnX" methods.</div><br><div \
class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, May 28, 2023 at \
1:02 PM John Hendrikx <<a \
href="mailto:john.hendrikx@gmail.com">john.hendrikx@gmail.com</a>> \
wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px \
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">When looking at the \
code for Scene#setOnKeyPressed, I noticed that it <br> calls Scene#setEventHandler. \
This is documented as:<br> <br>
/**<br>
* Sets the handler to use for this event type. There can only be <br>
one such<br>
* handler specified at a time. This handler is guaranteed to be called<br>
* first. This is used for registering the user-defined onFoo event<br>
* handlers.<br>
*<br>
* @param <T> the specific event class of the handler<br>
* @param eventType the event type to associate with the given <br>
eventHandler<br>
* @param eventHandler the handler to register, or null to unregister<br>
* @throws NullPointerException if the event type is null<br>
*/<br>
protected final <T extends Event> void setEventHandler(<br>
final EventType<T> eventType,<br>
final EventHandler<? super T> eventHandler) {<br>
<br>
Note that it specifically says "This handler is guaranteed to be called <br>
first."<br>
<br>
This function eventualy calls CompositeEventHandler#setEventHandler. <br>
This class tracks a chain of handlers, and reserves a special spot for a <br>
single special "eventHandler". Yet, in its dispatchBubblingEvent <br>
method, it clearly calls the "special" handler LAST... see below:<br>
<br>
public void dispatchBubblingEvent(final Event event) {<br>
final T specificEvent = (T) event;<br>
<br>
EventProcessorRecord<T> record = firstRecord;<br>
while (record != null) {<br>
if (record.isDisconnected()) {<br>
remove(record);<br>
} else {<br>
record.handleBubblingEvent(specificEvent);<br>
}<br>
record = record.nextRecord;<br>
}<br>
<br>
if (eventHandler != null) {<br>
eventHandler.handle(specificEvent);<br>
}<br>
}<br>
<br>
I've confirmed this with this small program (order of calls doesn't make <br>
a difference):<br>
<br>
public static class App extends Application {<br>
@Override<br>
public void start(Stage primaryStage) {<br>
Button button1 = new Button("111");<br>
<br>
HBox hBox = new HBox();<br>
hBox.getChildren().addAll(button1);<br>
Scene scene = new Scene(hBox, 300, 300);<br>
<br>
scene.addEventHandler(KeyEvent.KEY_PRESSED, e -> {<br>
System.out.println("KeyPressedHandler " + e);<br>
});<br>
scene.setOnKeyPressed(e -> {<br>
System.out.println("Main " + e);<br>
e.consume();<br>
});<br>
<br>
primaryStage.setScene(scene);<br>
primaryStage.show();<br>
}<br>
<br>
Which outputs the events not in the order documented:<br>
<br>
KeyPressedHandler KeyEvent [source = javafx.scene.Scene@36dbf594, target <br>
= Button@5dd3d27e[styleClass=button]'111', eventType = KEY_PRESSED, <br>
consumed = false, character = , text = f, code = F]<br>
Main KeyEvent [source = javafx.scene.Scene@36dbf594, target = <br>
Button@5dd3d27e[styleClass=button]'111', eventType = KEY_PRESSED, <br>
consumed = false, character = , text = f, code = F]<br>
<br>
--John<br>
<br>
</blockquote></div>
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