RFR: 8290040: Provide simplified deterministic way to manage listeners [v6]

[Kevin Rushforth]

On Tue, 18 Oct 2022 05:40:59 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>> private static final Object KEY = new Object();
>> 
>> public final ReadOnlyBooleanProperty shownProperty() {
>>   Object x = getProperties().get(KEY);
>>   if (x instanceof ReadOnlyBooleanProperty p) {
>>     return p;
>>   }
>>   ReadOnlyBooleanProperty p = ... // create
>>   getProperties().put(KEY, p);
>>   return p;
>> }
>
> Thanks, I understand, what I find odd is that this would be the first property in `Node` to be stored this way.  If this was so important, then why isn't this done for other properties? There seem to be sufficient candidates for this approach to "slim" down `Node` (infrequently used properties like `Subscene`, `id`, `style`, `blendMode`).
> 
> There's even a `MiscProperties` objects which is described as "Misc Seldom Used Properties" that is created only when needed with these properties:
> 
>         private LazyBoundsProperty boundsInParent;
>         private LazyBoundsProperty boundsInLocal;
>         private BooleanProperty cache;
>         private ObjectProperty<CacheHint> cacheHint;
>         private ObjectProperty<Node> clip;
>         private ObjectProperty<Cursor> cursor;
>         private ObjectProperty<DepthTest> depthTest;
>         private BooleanProperty disable;
>         private ObjectProperty<Effect> effect;
>         private ObjectProperty<InputMethodRequests> inputMethodRequests;
>         private BooleanProperty mouseTransparent;
>         private DoubleProperty viewOrder;
> 
> Let's see what others think before I change this. It does sound like a reasonable approach though.

I don't have time to review this as I am busy with JavaOne, so this is just a quick note to say that if there is sufficient benefit to add a `shown` property to the core of JavaFX, then it should be added _as_ a property -- possibly in MiscProperties if we think it is a seldom-used property. I don't like the idea of using `getProperties` for this.

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PR: https://git.openjdk.org/jfx/pull/830