RFR: 8294809: ListenerHelper for managing and disconnecting listeners [v9]

[Ajit Ghaisas]

On Fri, 4 Nov 2022 20:30:53 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> Introduction
>> 
>> There is a number of places where various listeners (strong as well as weak) are added, to be later disconnected in one go. For example, Skin implementations use dispose() method to clean up the listeners installed in the corresponding Control (sometimes using LambdaMultiplePropertyChangeListenerHandler class).
>> 
>> This pattern is also used by app developers, but there is no public utility class to do that, so every one must invent their own, see for instance
>> https://github.com/andy-goryachev/FxTextEditor/blob/master/src/goryachev/fx/FxDisconnector.java
>> 
>> Proposal
>> 
>> It might be beneficial to create a class (ListenerHelper, feel free to suggest a better name) which:
>> 
>> - provides convenient methods like addChangeListener, addInvalidationListener, addWeakChangeListener, etc.
>> - keeps track of the listeners and the corresponding ObservableValues
>> - provides a single disconnect() method to remove all the listeners in one go.
>> - optionally, it should be possible to add a lambda (Runnable) to a group of properties
>> - optionally, there should be a boolean flag to fire the lambda immediately
>> - strongly suggest implementing an IDisconnectable functional interface with a single disconnect() method
>> 
>> Make it Public Later
>> 
>> Initially, I think we could place the new class in package com.sun.javafx.scene.control; to be made publicly accessible later.
>> 
>> Where It Will Be Useful
>> 
>> [JDK-8294589](https://bugs.openjdk.org/browse/JDK-8294589) "MenuBarSkin: memory leak when changing skin"
>> and other skins, as a replacement for LambdaMultiplePropertyChangeListenerHandler.
>> 
>> https://github.com/openjdk/jfx/pull/908#:~:text=19%20hours%20ago-,8295175%3A%20SplitPaneSkinSkin%3A%20memory%20leak%20when%20changing%20skin%20%23911,-Draft
>> 
>> https://github.com/openjdk/jfx/pull/914
>
> Andy Goryachev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 24 additional commits since the last revision:
> 
>  - 8294809: review comments
>  - Merge remote-tracking branch 'origin/master' into 8294809.listener.helper
>  - 8294809: whitespace
>  - 8294809: no public api
>  - 8294809: map change listener
>  - Merge remote-tracking branch 'origin/master' into 8294809.listener.helper
>  - 8294809: generics
>  - 8294809: is alive
>  - Revert "8294809: removed weak listeners support"
>    
>    This reverts commit 2df4a85db638d76cacaf6c54ba669cdb3dd91a18.
>  - 8294809: removed weak listeners support
>  - ... and 14 more: https://git.openjdk.org/jfx/compare/fa19443d...470f42c1

modules/javafx.controls/src/main/java/com/sun/javafx/scene/control/ListenerHelper.java line 70:

> 68:  * </ul>
> 69:  */
> 70: public class ListenerHelper implements IDisconnectable {

This class is mixing two things- 
1. Managing listeners in a generic way - by providing ability to add & removeAll (via disconnect())
2. Trying to cater to *Skin specific requirement

Ideally, (2) above should be done separately. I mean, the class  ListenerHelper should not use `SkinBase`.
What do you think?

modules/javafx.controls/src/main/java/com/sun/javafx/scene/control/ListenerHelper.java line 87:

> 85: 
> 86:     public static ListenerHelper get(SkinBase<?> skin) {
> 87:         return accessor.apply(skin);

`accessor` can be `null` and needs to be checked.

modules/javafx.controls/src/test/java/test/javafx/scene/control/TestListenerHelper.java line 94:

> 92: 
> 93:     @Test
> 94:     public void testChangeListener_MultipleProperties() {

Should we address a hypothetical use case where the `ListenerHelper` has added a ChangeListener for 2 properties as done in this test case and wants to remove only ChangeListener for p1?
currently `h.disconnet()` removes ChangeListener of both the properties.

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PR: https://git.openjdk.org/jfx/pull/908