VirtualScrollPane causes exception during initial layout "java.util.NoSuchElementException: Cell ## is not visible"

[swpalmer]

Expected Behavior

Scroll bars for my CodeArea

Actual Behavior

Exception in Application start method
java.lang.reflect.InvocationTargetException
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:564)
	at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:464)
	at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:363)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:564)
	at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1071)
Caused by: java.lang.RuntimeException: Exception in Application start method
	at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:900)
	at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication$2(LauncherImpl.java:195)
	at java.base/java.lang.Thread.run(Thread.java:832)
Caused by: java.util.NoSuchElementException: Cell 2 is not visible
	at org.fxmisc.flowless.CellPositioner.getVisibleCell(CellPositioner.java:37)
	at org.fxmisc.flowless.Navigator.distanceFromGround(Navigator.java:373)
	at org.fxmisc.flowless.Navigator.fillViewportFrom(Navigator.java:333)
	at org.fxmisc.flowless.Navigator.visit(Navigator.java:131)
	at org.fxmisc.flowless.StartOffStart.accept(TargetPosition.java:85)
	at org.fxmisc.flowless.Navigator.layoutChildren(Navigator.java:80)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1207)
	at org.fxmisc.flowless.VirtualFlow.layoutChildren(VirtualFlow.java:257)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1207)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Scene.doLayoutPass(Scene.java:576)
	at javafx.graphics/javafx.scene.Scene.preferredSize(Scene.java:1750)
	at javafx.graphics/javafx.scene.Scene$2.preferredSize(Scene.java:393)
	at javafx.graphics/com.sun.javafx.scene.SceneHelper.preferredSize(SceneHelper.java:66)
	at javafx.graphics/javafx.stage.Window$12.invalidated(Window.java:1086)
	at javafx.base/javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:110)
	at javafx.base/javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:145)
	at javafx.graphics/javafx.stage.Window.setShowing(Window.java:1174)
	at javafx.graphics/javafx.stage.Window.show(Window.java:1189)
	at javafx.graphics/javafx.stage.Stage.show(Stage.java:273)

Reproducible Demo

This example gives a slightly different exception during layout. The horizontal scrollbar is misplaced and the layout is broken. In my full application the exception happens earlier - there is no initial layout, the start method fails and the app exits. If I remove the VirtualScrollPane the issue goes away. I'm having a a hard time making a small example that gives the exact error above.

public class Bug extends Application {

 public static void main(String [] args) {
     launch(args);
 }

 public void start(Stage stage) {
        CodeArea editor = new CodeArea();

        try {
            // Use the path of some file that doesn't fit in the view
            editor.appendText(Files.readString(Path.of("\\pick\\a\\file\\Bug.java")));
        } catch (IOException ex) {
            System.err.println("Crap..." + ex);
        }
        editor.setParagraphGraphicFactory(LineNumberFactory.get(editor));
        editor.setLineHighlighterOn(true);

        Region wrapper = new Pane(new VirtualizedScrollPane<>(editor));
        editor.prefWidthProperty().bind(wrapper.widthProperty());
        editor.prefHeightProperty().bind(wrapper.heightProperty());

        Tab tab = new Tab("Editor", wrapper);
        TabPane tabs = new TabPane(tab);
        SplitPane splitter = new SplitPane(new Label("placeholder"), tabs);
        BorderPane bp = new BorderPane(splitter);

        Scene scene = new Scene(bp);
        stage.setScene(scene);
        stage.setWidth(800);
        stage.setHeight(600);
        stage.setTitle("VirtualScrollPane Layout Issue");
        stage.show();
    }

}

Environment info:

• RichTextFX Version: 0.10.5
• Operating System: Windows 10 Pro 64-bit
• Java version: openjdk version "15.0.1" 2020-10-20 OpenJDK Runtime Environment Zulu15.28+51-CA (build 15.0.1+9) OpenJDK 64-Bit Server VM Zulu15.28+51-CA (build 15.0.1+9, mixed mode, sharing) ("JDK FX" version)

---

Current Workarounds

Have not been able to get VirtualScrollPane to work without issues. Scrolling works via trackpad without it though.

[Jugen]

If I'm not mistaken a clunky workaround is to only add the VirtualizedScrollPane to the Scene after the Stage is shown.

[Jugen]

Sorry, a better workaround would be to only add/append the text to the editor AFTER the scene/stage is shown.

[swpalmer]

That does seem to work for the initial exception. However now I notice that scrolling is not as smooth, particularly in the horizontal direction, and I've seen several occurrences of this exception:

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException: Cannot invoke "org.fxmisc.richtext.model.Paragraph.length()" because "this.paragraph" is null
	at org.fxmisc.richtext.ParagraphText.getClampedCaretPosition(ParagraphText.java:319)
	at org.fxmisc.richtext.ParagraphText.getCurrentLineStartPosition(ParagraphText.java:295)
	at org.fxmisc.richtext.ParagraphBox.getCurrentLineStartPosition(ParagraphBox.java:179)
	at org.fxmisc.richtext.GenericStyledArea.getCurrentLineStartInParargraph(GenericStyledArea.java:1185)
	at org.fxmisc.richtext.GenericStyledArea.lambda$setLineHighlighterOn$36(GenericStyledArea.java:1255)
	at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:428)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
	at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$11(PlatformImpl.java:427)
	at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
	at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
	at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
	at java.base/java.lang.Thread.run(Thread.java:832)

When resizing the window, it eventually locks up the layout with this exception:

Exception in thread "JavaFX Application Thread" java.util.NoSuchElementException: No value present
	at java.base/java.util.Optional.get(Optional.java:141)
	at org.fxmisc.flowless.CellListManager.getPresentCell(CellListManager.java:65)
	at org.fxmisc.flowless.CellPositioner.getVisibleCell(CellPositioner.java:33)
	at org.fxmisc.flowless.Navigator.distanceFromGround(Navigator.java:373)
	at org.fxmisc.flowless.Navigator.fillViewportFrom(Navigator.java:333)
	at org.fxmisc.flowless.Navigator.visit(Navigator.java:131)
	at org.fxmisc.flowless.StartOffStart.accept(TargetPosition.java:85)
	at org.fxmisc.flowless.Navigator.layoutChildren(Navigator.java:80)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1207)
	at org.fxmisc.flowless.VirtualFlow.layoutChildren(VirtualFlow.java:257)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1207)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Parent.layout(Parent.java:1214)
	at javafx.graphics/javafx.scene.Scene.doLayoutPass(Scene.java:576)
	at javafx.graphics/javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:2476)
	at javafx.graphics/com.sun.javafx.tk.Toolkit.lambda$runPulse$2(Toolkit.java:413)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
	at javafx.graphics/com.sun.javafx.tk.Toolkit.runPulse(Toolkit.java:412)
	at javafx.graphics/com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:439)
	at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:563)
	at javafx.graphics/com.sun.javafx.tk.quantum.PaintCollector.liveRepaintRenderJob(PaintCollector.java:327)
	at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$ViewEventNotification.run(GlassViewEventHandler.java:883)
	at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$ViewEventNotification.run(GlassViewEventHandler.java:843)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
	at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleViewEvent$15(GlassViewEventHandler.java:924)
	at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:412)
	at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleViewEvent(GlassViewEventHandler.java:923)
	at javafx.graphics/com.sun.glass.ui.View.handleViewEvent(View.java:540)
	at javafx.graphics/com.sun.glass.ui.View.notifyResize(View.java:880)
	at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
	at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
	at java.base/java.lang.Thread.run(Thread.java:832)

[Jugen]

I think the current master version (to be released as 0.10.6 end of January) addresses the NullPointerException and maybe also the NoSuchElementException.

[Jugen]

Please test with the latest version (0.10.6) that's been released now, and give feedback if needed.

[Glavo]

Please test with the latest version (0.10.6) that's been released now, and give feedback if needed.

@Jugen I still get these confusing exceptions in 0.10.8.

[Glavo]

Ah, when I repeatedly open a file in my editor, when I use RichTextFX 0.10.8, an exception occurs probabilistically and the opening fails. Exceptions that may occur are NullPointerException, NoSuchElementException·， IndexOutOfBoundsExceptionandConcurrentModificationException`.

I just tried updating to 0.10.9 and I was surprised that these exceptions no longer occur, although this fix is not mentioned at all in the changelog. Unfortunately, I also need to be compatible with Java 8, so I can't upgrade for the time being.