RFR: 8294809: ListenerHelper for managing and disconnecting listeners [v8]

[Kevin Rushforth]

On Mon, 31 Oct 2022 16:45:51 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 incrementally with one additional commit since the last revision:
> 
>   8294809: whitespace

@arapte and @aghaisas Can you also review this? It really needs to be done in connection with one of the existing Draft PRs that will take advantage of it, such as PR #925 , since the purpose is to make it easier for skins to avoid memory leaks.

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