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Hi, I created a PR to optimize the memory footprint of event handler properties and simplify the code: https: //github. com/openjdk/jfx/pull/2088 I'd like to hear everyone's opinions. ## Summary This PR moves the event handler properties</div>
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<div dir="ltr"><div dir="ltr">Hi,<br><div><br></div><div>I created a PR to optimize the memory footprint of event handler properties and simplify the code: <a href="https://github.com/openjdk/jfx/pull/2088">https://github.com/openjdk/jfx/pull/2088</a></div><div>I'd like to hear everyone's opinions.</div><div><br></div><div>## Summary<br><br>This PR moves the event handler properties of `Node` and its subclasses to `EventHandlerManager` for storage.<br><br>## Goals<br><br>- More lazy allocation of property objects.<br>- Simplify the way to define event handler properties.<br>- Maintain consistency between the actual event handler value and the property value.<br><br>## Motivation<br><br>In JavaFX, many controls define event handler properties.<br><br>For example, `ButtonBase` defines an `onAction` property:<br><br>```java<br>public final ObjectProperty<EventHandler<ActionEvent>> onActionProperty() { return onAction; }<br><br>public final void setOnAction(EventHandler<ActionEvent> value) { onActionProperty().set(value); }<br><br>public final EventHandler<ActionEvent> getOnAction() { return onActionProperty().get(); }<br><br>private ObjectProperty<EventHandler<ActionEvent>> onAction = new ObjectPropertyBase<>() {<br> @Override protected void invalidated() {<br> setEventHandler(ActionEvent.ACTION, get());<br> }<br><br> @Override<br> public Object getBean() {<br> return ButtonBase.this;<br> }<br><br> @Override<br> public String getName() {<br> return "onAction";<br> }<br>};<br>```<br><br>However, there are several issues with defining properties in this way.<br><br>### Unnecessary allocation of `ObjectProperty` objects<br><br>Users often call the `setOnAction` method to set the event handler, but rarely call `onActionProperty()` to add listeners or bind it to other values.<br><br>The actual effect of `setOnAction` is to call `EventHandlerManager#setEventHandler(...)` to install the event handler in the `EventHandlerManager`, and the installed event handler can also be retrieved by calling `EventHandlerManager#getEventHandler(...)`.<br><br>Therefore, allocating the `ObjectProperty` object before the user explicitly calls `onActionProperty()` wastes memory and serves no real purpose. Most of these objects can be optimized away.<br><br>### The property value and EventHandlerManager may be out of sync<br><br>Consider the following code:<br><br>```java<br>EventHandler<ActionEvent> handler = event -> IO.println("On Action");<br><br>var button = new Button() {<br> {<br> setOnAction(handler);<br> setEventHandler(ActionEvent.ACTION, null);<br> }<br>};<br><br>assert button.getOnAction() == handler;<br><br>button.fire(); // Nothing happened<br>```<br><br>As you can see, the handler obtained by `getOnAction()` may not be triggered, <br>because the value of the `onActionProperty()` property is actually not associated with the handler stored in the `EventHandlerManager`. <br>Users can override the value of `onActionProperty()` by calling `setEventHandler(...)`, which may lead to unexpected behavior.<br><br>### Defining event handler properties is verbose and cumbersome<br><br>Each time a user defines an event handler property, they need to declare a subclass of `ObjectPropertyBase` and repeat some boilerplate code.<br>This is cumbersome to write and prone to errors.<br><br>## Description<br><br>This PR adds the following APIs to the `Node` class:<br><br>```java<br>protected final <T extends Event> EventHandler<? super T> getEventHandler(<br> final EventType<T> eventType) {<br> return getInternalEventDispatcher().getEventHandlerManager().getEventHandler(eventType);<br>}<br> <br>protected final <T extends Event> ObjectProperty<EventHandler<? super T>> eventHandlerProperty(<br> final EventType<T> eventType,<br> final String name) {<br> return getInternalEventDispatcher().getEventHandlerManager()<br> .eventHandlerProperty(eventType, name);<br>}<br>```<br><br>After this, defining event handler properties in the `Node` class and its subclasses only requires the following:<br><br>```java<br>public final void setOnMouseClicked(EventHandler<? super MouseEvent> value) {<br> setEventHandler(MouseEvent.MOUSE_CLICKED, value);<br>}<br><br>public final EventHandler<? super MouseEvent> getOnMouseClicked() {<br> return getEventHandler(MouseEvent.MOUSE_CLICKED);<br>}<br><br>public final ObjectProperty<EventHandler<? super MouseEvent>> onMouseClickedProperty() {<br> return eventHandlerProperty(MouseEvent.MOUSE_CLICKED, "onMouseClicked");<br>}<br>```<br><br>In this way, calling `setOnMouseClicked(...)` will not invoke `onMouseClickedProperty()`, and the corresponding `ObjectProperty` will not be allocated.<br>The `ObjectProperty` will only be allocated and stored inside the `EventHandlerManager` when the user explicitly calls `onMouseClickedProperty()`.<br><br>The three methods `eventHandlerProperty(...)`, `getEventHandler(...)`, and `setEventHandler(...)` follow the JavaFX property conventions.<br>Calling `setEventHandler(...)` will also trigger listeners added to `eventHandlerProperty(...)`.<br><br>## Risks and Assumptions<br><br>This PR adds `getEventHandler(...)` and `eventHandlerProperty(...)` methods to the `Node` class. <br>If a user defines methods with the same signatures in a subclass of `Node`,<br>the subclass will fail JVM verification.<br><br>This PR changes the behavior of the `Node#setEventHandler(...)` method.<br>Now it's behavior is equivalent to `node.eventHandlerProperty(...).set(...)`. <br>Calling it will affect the corresponding property value, trigger listeners added to the property, and throw an exception if the property is bound.<br><br></div></div>
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