Node.lookupAll behaves differently before Scene is shown

[Scott Palmer]

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@16bca2d9[styleClass=split-pane]]
After showing:
Found 3 SpitPanes: [SplitPane@16bca2d9[styleClass=split-pane], 
SplitPane@7078ef3c[styleClass=split-pane], 
SplitPane@56a29626[styleClass=split-pane]]


Regards,

Scott