Android Animation duration cannot be negative in AndroidViewContainer.transitionToX

[AndreiGorelov]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

On Android I am seeing a crash with IllegalArgumentException: "Animation duration cannot be negative". When playback is running and the beat cursor moves, or when the user interacts with the score (scrolling playback fragment to off-screen) and alphaTab triggers cursor scroll/animation, the app sometimes crashes with:

java.lang.IllegalArgumentException: Animation duration cannot be negative
at android.view.animation.Animation.setDuration(Animation.java:466)
at alphaTab.platform.android.AndroidViewContainer.transitionToX$lambda$0(AndroidViewContainer.kt:182)
at alphaTab.platform.android.AndroidViewContainer$$ExternalSyntheticLambda1.invoke(D8$$SyntheticClass:0)
at alphaTab.platform.android.AndroidUiFacade.beginInvoke$lambda$0(AndroidUiFacade.kt:348)
at alphaTab.platform.android.AndroidUiFacade$$ExternalSyntheticLambda5.run(D8$$SyntheticClass:0)
at android.os.Handler.handleCallback(Handler.java:942)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loopOnce(Looper.java:226)
at android.os.Looper.loop(Looper.java:313)
at android.app.ActivityThread.main(ActivityThread.java:8810)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:604)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1067)

Expected Behavior

Even if alphaTab computes a negative duration, the android view should not crash. The animation duration probably should be clamped to non‑negative values.

Steps To Reproduce

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

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 a MusicXML score
4. Start playback
5. Scroll the score's playing fragment to off-screen

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?

Possible Fix:
In my fork I fixed this by clamping the duration to at least 0 on the Android side AndreiGorelov@56cfdef

[Danielku15]

Clamping the duration is a good patch for this problem. Do you have the exact files available where it happens for you? I'd like to check also the root cause on how we can get negative durations there. Maybe we can handle this already in the alphaTab core areas.

[AndreiGorelov]

It doesn’t seem to depend on a specific file — the issue occurred with any of the ones I tested. I was able to reproduce it reliably by:

• starting playback with both the cursor and autoscroll enabled
• then scrolling the document during playback so that the currently played area moves outside the visible screen

Still, I’ve attached a few of the files I used for testing. Please note the file  8af43131c88cdfeaa9693e3912a120a1.mxl  — with this one, the cursor doesn’t work at all. I haven’t investigated the cause yet (I might open a separate issue later).
At the moment, I’m also investigating a possible memory leak in AndroidAudioWorker/AndroidSynthOutput with xml/mxl files and will share my findings in another issue.

scores.zip

If you’re not able to reproduce the problem, please let me know — I can try to create a minimal demo app similar to my project (it’s mostly based on your examples and documentation).

Thanks for checking this!