RFR: 8294809: ListenerHelper for managing and disconnecting listeners [v13]

[Kevin Rushforth]

On Wed, 23 Nov 2022 17:18:47 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: review comments

Looks OK, although I left another comment on the (now less so) redundant test.

modules/javafx.controls/src/test/java/test/javafx/scene/control/TestListenerHelper.java line 283:

> 281:         AtomicInteger ct = new AtomicInteger();
> 282: 
> 283:         h.addInvalidationListener(() -> ct.incrementAndGet(), p);

Now this is somewhat redundant with `testInvalidationListener_MultipleProperties`, since it tests the same flavor of method -- unlike `addChangeListener`, there are only two patterns for `addInvalidationListener`, not three. Although showing that it works with a single property is possibly useful (the same could be said for the ChangeListener tests), so I don't mind if you prefer to keep it.

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Marked as reviewed by kcr (Lead).

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