RFR: 8252935: Add treeShowing listener only when needed [v4]

[Jeanette Winzenburg]

On Wed, 10 Feb 2021 14:53:20 GMT, Jeanette Winzenburg <fastegal at openjdk.org> wrote:

>> Sadly, there is no way to view just the failures -- at least not right now. What I do is open the raw log and look for "FAILED" (all caps).
>> 
>> I'll file an RFE to see whether we can produce a summary of the test failures, but I won't have time to look at it right away.
>
> thanks for the info :)

> I could extract the methods instead if you donot like me passing in `null` for the `ObservableValue`, it would then look like:
> 
> ```
>     sceneChanged(null, node.getScene());  // register chain
> 
>     sceneChanged(node.getScene(), null);  // unregister chain
> ```
> 

That's a good pattern, IMO (biased, using it in my own code)

> 
> Also I should mention that this is not Skin code in case it was missed.

No, it was not missed :)  Aside: actually, we cannot use the pattern above in skin code because we are using LambdaMultipleListenerHandler to un/register for change notification. The consumer that's registered carries only the observable, consequently its old value is not available at notification time. Which forces keeping the old value stored in the skin, if interested in changes from a "path" property.

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PR: https://git.openjdk.java.net/jfx/pull/185