Node.lookupAll behaves differently before Scene is shown

[Scott Palmer]

That’s interesting.  It leads me to wonder what is the expected result from a call to lookupAll in various scenarios.  If, after the window was showing, the SplitPane divider is pushed all the way to one size such that the skin can potentially choose to leave the hidden child out of the scene graph, presumable the current lookupAll implementation would then fail to find it again.

I think that either that’s a bug, or it needs to be made clearer in the documentation that non-rendered child nodes may not be found.  I personally lean toward “bug”, as I think any Node reachable through a parent Node’s public API to access child nodes should be found via Node.lookupAll.  I suppose you could argue that Scene.lookup is searching the scene graph in a more literal sense and wouldn’t find some Nodes.

The docs for Scene.lookup say:
	"Looks for any node within the scene graph based on the specified CSS selector.”

The docs for Node.lookup say:
	"Finds this Node, or the first sub-node, based on the given CSS selector”

The docs for Node.lookupAll say:
	"Finds all Nodes, including this one and any children, which match the given CSS selector."

It doesn’t mention the scene graph or if the node is currently being rendered in a visible portion of the scene.  It explicitly states “any children”.

So I’m saying it’s a bug.


Scott

> On Dec 24, 2022, at 3:34 AM, John Hendrikx <john.hendrikx at gmail.com> wrote:
> 
> Hi,
> 
> In this case, this is because SplitPane doesn't actually add its split items as children -- only its Skin does this.  Skins are AFAIK installed after a CSS pass.
> 
> In the split pane case, I guess a Skin could choose to completely leave out a child if its splitter completely hides it (ie, dragged all the way to the left or right if allowed).
> 
> This may be another case where it may make sense to have both a document graph (logical graph) and a scene graph as Michael Strauss mentioned here: https://mail.openjdk.org/pipermail/openjfx-dev/2022-June/034417.html
> 
> I doubt this is documented anywhere at all, it's one of those things that doesn't work quite right in JavaFX before a Scene is displayed.
> 
> --John
> 
> On 23/12/2022 23:49, Scott Palmer wrote:
>> I just want to make sure this is not expected behaviour. I don’t think so, the documentation for lookupAll doesn’t mention anything related, but maybe I missed something somewhere else.
>> 
>> I was just coding something to query the Scene for all SplitPanes and save/restore the divider positions for when my application is exiting and launching and came across this issue.
>> My UI is fully constructed (at least in terms of all the SplitPanes in the scene graph) before it is shown.
>> 
>> This  code:
>> 
>> 	window.getScene().getRoot().lookupAll(".split-pane")
>> 
>> returns a different number of Nodes if I call it before showing the window versus after showing the window.  Specifically, if I call it before showing the window it appears to only return the first SplitPane found in the scene graph, but calling it in an event handler for the window shown event I get all three.
>> 
>> This can be demonstrated with the following program:
>> 
>> 
>> import javafx.application.Application;
>> import javafx.scene.Scene;
>> import javafx.scene.control.SplitPane;
>> import javafx.scene.control.TextArea;
>> import javafx.scene.layout.BorderPane;
>> import javafx.stage.Stage;
>> import javafx.stage.Window;
>> 
>> public class LookupAll extends Application {
>>     Window mainWindow;
>>     
>>     public static void main(String[] args) {
>>         launch(args);
>>     }
>>     
>>     @Override
>>     public void start(Stage primaryStage) throws Exception {
>>         var bp = new BorderPane(new SplitPane(new TextArea(),new SplitPane(new TextArea(),new SplitPane(new TextArea()))));
>>         var scene = new Scene(bp);
>>         primaryStage.setScene(scene);
>>         mainWindow = primaryStage;
>>         System.out.println("Before showing:");
>>         countSplitPanes();
>>         primaryStage.setOnShown(we -> {
>>             System.out.println("After showing:");
>>             countSplitPanes();
>>         });
>>         primaryStage.show();
>>     }
>>     
>>     private void countSplitPanes() {
>>         var splitPanes = mainWindow.getScene().getRoot().lookupAll(".split-pane");
>>         System.out.printf("Found %d SpitPanes: %s\n",splitPanes.size(), splitPanes);
>>     }
>> }
>> 
>> 
>> 
>> Before showing:
>> Found 1 SpitPanes: [SplitPane at 16bca2d9[styleClass=split-pane]]
>> After showing:
>> Found 3 SpitPanes: [SplitPane at 16bca2d9[styleClass=split-pane], SplitPane at 7078ef3c[styleClass=split-pane], SplitPane at 56a29626[styleClass=split-pane]]
>> 
>> 
>> Regards,
>> 
>> Scott
>> 

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