Android: some MusicXML files fail to fully render and cursor becomes unusable (works on Web)

[AndreiGorelov]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

On Android, this attached MusicXML file does not render fully, and cursor functionality is not usable because rendering fails.
The same file renders correctly in the Web target (tested on https://alphatab.net/).

score.xml

Expected Behavior

The same MusicXML should render fully on Android, and cursor behavior should work normally (including playback/user interaction scenarios), just like in Web target.

Steps To Reproduce

1. Create a simple Android app screen that hosts alphaTab
2. Enable user interaction and cursor in settings, for example:

val settings = alphaTab.Settings().apply {
            player.playerMode = PlayerMode.EnabledAutomatic
            player.enableCursor = true
            player.enableAnimatedBeatCursor = true
            player.enableUserInteraction = true
            player.scrollMode = ScrollMode.OffScreen
            display.scale = 0.8
        }

3. Load the attached MusicXML file (score.xml).
4. Observe that rendering is incomplete/fails and cursor behavior is broken on Android.

Link to jsFiddle, CodePen, Project

No response

Version and Environment

1. alphaTab version: 1.8.1
2. Platform: Android (Kotlin)
3. Devices: Android 14/16 tablet and phone

Platform

Android (Native)

Anything else?

I got stack traces from AlphaTabApiBase.onError on Android for the same file:

• NullPointerException

 0 = {StackTraceElement@34817} "alphaTab.rendering.utils.AccidentalHelper.getNoteSteps(AccidentalHelper.kt:240)"
 1 = {StackTraceElement@34818} "alphaTab.rendering.ScoreBarRenderer.getNoteSteps(ScoreBarRenderer.kt:383)"
 2 = {StackTraceElement@34819} "alphaTab.rendering.glyphs.ScoreBeatGlyph._createNoteGlyphs(ScoreBeatGlyph.kt:307)"
 3 = {StackTraceElement@34820} "alphaTab.rendering.glyphs.ScoreBeatGlyph._createGlyphs(ScoreBeatGlyph.kt:251)"
 4 = {StackTraceElement@34821} "alphaTab.rendering.glyphs.ScoreBeatGlyph.doLayout(ScoreBeatGlyph.kt:218)"
 5 = {StackTraceElement@34822} "alphaTab.rendering.glyphs.BeatContainerGlyph.doLayout(BeatContainerGlyph.kt:216)"
 6 = {StackTraceElement@34823} "alphaTab.rendering.ScoreBeatContainerGlyph.doLayout(ScoreBeatContainerGlyph.kt:99)"
 7 = {StackTraceElement@34824} "alphaTab.rendering.glyphs.MultiVoiceContainerGlyph.doLayout(MultiVoiceContainerGlyph.kt:335)"
 8 = {StackTraceElement@34825} "alphaTab.rendering.BarRendererBase.createBeatGlyphs(BarRendererBase.kt:641)"
 9 = {StackTraceElement@34826} "alphaTab.rendering.BarRendererBase.doLayout(BarRendererBase.kt:444)"
 10 = {StackTraceElement@34827} "alphaTab.rendering.LineBarRenderer.doLayout(LineBarRenderer.kt:111)"
 11 = {StackTraceElement@34828} "alphaTab.rendering.staves.RenderStaff.addBar(RenderStaff.kt:244)"
 12 = {StackTraceElement@34829} "alphaTab.rendering.staves.StaffSystem.addBars(StaffSystem.kt:232)"
 13 = {StackTraceElement@34830} "alphaTab.rendering.layout.VerticalLayoutBase._createStaffSystem(VerticalLayoutBase.kt:426)"
 14 = {StackTraceElement@34831} "alphaTab.rendering.layout.VerticalLayoutBase._layoutAndRenderScore(VerticalLayoutBase.kt:315)"
 15 = {StackTraceElement@34832} "alphaTab.rendering.layout.VerticalLayoutBase.doLayoutAndRender(VerticalLayoutBase.kt:75)"
 16 = {StackTraceElement@34833} "alphaTab.rendering.layout.ScoreLayout.layoutAndRender(ScoreLayout.kt:143)"
 17 = {StackTraceElement@34834} "alphaTab.rendering.ScoreRenderer._layoutAndRender(ScoreRenderer.kt:279)"
 18 = {StackTraceElement@34835} "alphaTab.rendering.ScoreRenderer.render(ScoreRenderer.kt:244)"
 19 = {StackTraceElement@34836} "alphaTab.rendering.ScoreRenderer.renderScore(ScoreRenderer.kt:153)"
 20 = {StackTraceElement@34837} "alphaTab.rendering.ScoreRendererWrapper.renderScore(ScoreRendererWrapper.kt:159)"
 21 = {StackTraceElement@34838} "alphaTab.AlphaTabApiBase.render(AlphaTabApiBase.kt:556)"
 22 = {StackTraceElement@34839} "alphaTab.AlphaTabApiBase._internalRenderTracks(AlphaTabApiBase.kt:429)"
 23 = {StackTraceElement@34840} "alphaTab.AlphaTabApiBase.renderScore(AlphaTabApiBase.kt:386)"
 24 = {StackTraceElement@34841} "alphaTab.AlphaTabApiBase.renderScore$default(AlphaTabApiBase.kt:348)"
 25 = {StackTraceElement@34842} "alphaTab.AlphaTabView.renderTracks(AlphaTabView.kt:115)"
 26 = {StackTraceElement@34843} "alphaTab.AlphaTabView.setTracks(AlphaTabView.kt:29)"

• ClassCastException

0 = {StackTraceElement@34703} "alphaTab.model.MusicFontSymbol$Companion.fromValue(MusicFontSymbol.kt:621)"
1 = {StackTraceElement@34704} "alphaTab.rendering.LineBarRenderer._paintTupletHelper(LineBarRenderer.kt:371)"
2 = {StackTraceElement@34705} "alphaTab.rendering.LineBarRenderer.paintTuplets(LineBarRenderer.kt:224)"
3 = {StackTraceElement@34706} "alphaTab.rendering.LineBarRenderer.paintTuplets$default(LineBarRenderer.kt:216)"
4 = {StackTraceElement@34707} "alphaTab.rendering.LineBarRenderer.paintContent(LineBarRenderer.kt:137)"
5 = {StackTraceElement@34708} "alphaTab.rendering.BarRendererBase.paint(BarRendererBase.kt:560)"
6 = {StackTraceElement@34709} "alphaTab.rendering.staves.RenderStaff.paint(RenderStaff.kt:368)"
7 = {StackTraceElement@34710} "alphaTab.rendering.staves.StaffSystem.paintPartial(StaffSystem.kt:579)"
8 = {StackTraceElement@34711} "alphaTab.rendering.staves.StaffSystem.paint(StaffSystem.kt:533)"
9 = {StackTraceElement@34712} "alphaTab.rendering.layout.VerticalLayoutBase._paintSystem$lambda$0(VerticalLayoutBase.kt:344)"
10 = {StackTraceElement@34713} "alphaTab.rendering.layout.VerticalLayoutBase$$ExternalSyntheticLambda1.invoke(D8$$SyntheticClass:0)"
11 = {StackTraceElement@34714} "alphaTab.rendering.layout.ScoreLayout._internalRenderLazyPartial(ScoreLayout.kt:179)"
12 = {StackTraceElement@34715} "alphaTab.rendering.layout.ScoreLayout.renderLazyPartial(ScoreLayout.kt:190)"
13 = {StackTraceElement@34716} "alphaTab.rendering.ScoreRenderer.renderResult(ScoreRenderer.kt:195)"
14 = {StackTraceElement@34717} "alphaTab.rendering.ScoreRendererWrapper.renderResult(ScoreRendererWrapper.kt:166)"
15 = {StackTraceElement@34718} "alphaTab.platform.android.AndroidUiFacade.initialize$lambda$0(AndroidUiFacade.kt:123)"
16 = {StackTraceElement@34719} "alphaTab.platform.android.AndroidUiFacade$$ExternalSyntheticLambda6.invoke(D8$$SyntheticClass:0)"
17 = {StackTraceElement@34720} "alphaTab.platform.android.AlphaTabRenderSurface.onLayout(AlphaTabRenderSurface.kt:159)"

[AndreiGorelov]

I’ve made fixes in my fork for this issue:

• NullPointerException in  AccidentalHelper.getNoteSteps AndreiGorelov@bea62a3
  As I understand, the issue on Android stems from the processing order. I suspect my fix doesn’t address the root cause perfectly, but I couldn’t come up with a better solution yet (still getting familiar with the codebase).
• ClassCastException in LineBarRenderer._paintTupletHelper AndreiGorelov@681c64b

  From what I can tell, the attached file contains non-standard tuplets (12:27) that the previous logic didn’t account for. Additionally, Kotlin’s stricter type handling triggered the error. Unfortunately, I don’t have a musical background, so I’m not entirely confident in the quality of my fix.

[AndreiGorelov]

Maybe these non‑standard “time signatures” don’t need to be displayed at all?

How it looks now:

• https://alphatab.net/

• Android app with my fixes

• MuseScore (similar file)

• Some PDF version