Threading and Node.lookup

[Tom Schindl]

Hi,

The problem is that the lookup system depends on the CSS-Engine (you can
pass any CSS-Selector!) to having processed the Node.

My guess is that the CSS-Engine does only processes nodes when they are
attached to the Scene (there's no reason for it to process them if they
are not attached).

Tom

Am 20.03.13 04:47, schrieb Scott Palmer:
> Yes, good point.  In that case I could delay the connection to the Scene object and instead do the lookup via the root node.  But still in this case, has a rendering pass ("pulse") happened yet on such a Scene?  Since Scene objects must be constructed and modified on the FX app thread I guess it makes sense that they would do an initial layout pass on the root node?  So perhaps John is correct.  It's late and I don't have time to construct a test case now.
> 
> Scott
> 
> 
> On 2013-03-19, at 10:35 PM, Kevin Rushforth <kevin.rushforth at oracle.com> wrote:
> 
>>> Node background = scene.lookup("#background");
>>
>> Note that this particular call references a scene, so must be done on the FX application thread. You should not touch the scene or a node that is connected to a scene on a background thread.
>>
>> -- Kevin
>>
>>
>>
>> Scott Palmer wrote:
>>>
>>> On 2013-03-19, at 8:30 PM, John Smith <John_Smith at symantec.com> wrote:
>>>   
>>>> "the node lookup function doesn't function (just returns null) until a rendering pass has been run on the scene"
>>>>     
>>>
>>>
>>> I don't think that is exactly right.  I'm sure I used the lookup method to grab nodes from a scene graph that I made with Scene Builder *prior* to showing it.
>>>
>>> Yep… I just checked my code, this doesn't return nulls:
>>>
>>> …
>>> Parent root = FXMLLoader.load(location);
>>> Scene scene = new Scene(root);
>>> Node top = scene.lookup("#top");
>>> Node background = scene.lookup("#background");
>>> …
>>>
>>> The Scene clearly was just constructed and isn't showing or part of a Stage.
>>> The only difference is that this is called on the Platform thread. So something must be happening that needs to run on the Platform thread.
>>>
>>> You are correct about the width/height stuff that requires a layout pass to have happened before you get reasonable values.
>>>
>>> Scott
>>>
>>>
>>>
>>>   
>>>> +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
>>>>>>>
>>>>>>>           
>>>>>       
>>>
>>>   
> 


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