Threading and Node.lookup

[John Smith]

+1 to Philipp's question.

It's always been the case that the node lookup function doesn't function (just returns null) until a rendering pass has been run on the scene.

With Philipp's sample at (https://gist.github.com/phdoerfler/5201162) , if you implemented it as an Application, placed the item to be looked up in a stage, and called lookup only *after* you called stage.show on your scene, then the lookup would work (without requiring Platform.runLater) - so some side effect of showing the scene on the stage allows nodes in the scene to be looked up.

It works the same way as trying to get the height and width of a node before it has been shown on stage - that also does not really work as you might expect because the css needs to be processed in the rendering pass to accurately determine the height and width.  I understand why height and width work the way they do, but I was never really sure why lookup doesn't just work immediately and the delayed behavior isn't documented anywhere.

Likely there is some hidden impl_ function you could use to trigger the rendering pass, after which the lookup would work.

- John

-----Original Message-----
From: openjfx-dev-bounces at openjdk.java.net [mailto:openjfx-dev-bounces at openjdk.java.net] On Behalf Of Kevin Rushforth
Sent: Tuesday, March 19, 2013 4:50 PM
To: Philipp Dörfler
Cc: openjfx-dev at openjdk.java.net List
Subject: Re: Threading and Node.lookup

One of the scene graph or FXML folks should be able to reply.

-- Kevin


Philipp Dörfler wrote:
> Ok, threading aside: Where's my mistake?
>
> https://gist.github.com/phdoerfler/5201162
>
> ~ philipp
>
> Am 20.03.2013 um 00:30 schrieb Kevin Rushforth <kevin.rushforth at oracle.com>:
>
>   
>>> As to my understanding, one only has to use Platform.runLater for accessing nodes already attached to a Scene.
>>>       
>> In general is is legal to call accessor and mutator methods on a Node not attached to a Scene from any thread. I don't specifically know whether lookup does anything that would add additional threading restrictions.
>>
>> -- Kevin
>>
>>
>> Philipp Dörfler wrote:
>>     
>>> Hi,
>>>
>>> does fooNode.lookup("#bar") have to be called using Platform.runLater if fooNode is not attached to any Scene?
>>> As to my understanding, one only has to use Platform.runLater for accessing nodes already attached to a Scene.
>>>
>>> However, fooNode.lookup seems to fail (= return null) for nodes which are not contained directly in it, but in another node (in my case: a ScrollPane), which is then contained in fooNode. The scene graph was provided by FXMLLoader.load(...).
>>>
>>> Placing those lookups in Platform.runLater suddenly causes them to work.
>>>
>>> This feels like an arcane bug to me, but I might be missing some core concepts.
>>> So - did I miss something or is this a bug?
>>>
>>> Cheers,
>>> Philipp
>>>       
>
>