Assertion Error using CustomScrollView with CupertinoSliverNavigationBar (Flutter 3.29)

Steps to reproduce

When scrolling on the CupertinoSliverNavigationBar, an assertion error occurs randomly. The issue arises after performing multiple scroll gestures on the navigation bar in both directions. The following assertion errors are thrown:

'package:flutter/src/widgets/scrollable.dart': Failed assertion: line 875 pos 12: '_hold == null': is not true.
'package:flutter/src/widgets/scrollable.dart': Failed assertion: line 880 pos 12: '_hold == null || _drag == null': is not true.

Steps to Reproduce:

Run the provided code.
Scroll up or down on the navigation bar multiple times.
Observe the assertion errors in the debug console.
Attempt to scroll again—scrolling is now completely broken.

Code:

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
      ),
      home: Scaffold(
        body: CustomScrollView(
          slivers: [
            CupertinoSliverNavigationBar(
                largeTitle: Text("Example"),
            ),
          ],
        ),
      ),
    );
  }
}

Expected results

Regardless of the scrolling movement, no errors should be thrown.

Actual results

Assertion errors occur, and the scrolling state becomes unresponsive.

Code sample

Example

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
      ),
      home: Scaffold(
        body: CustomScrollView(
          slivers: [
            CupertinoSliverNavigationBar(
                largeTitle: Text("Example"),
            ),
          ],
        ),
      ),
    );
  }
}

Screenshots or Video

Screenshots / Video demonstration

413289971-3b229b1f-37b1-418d-9fbd-dc95be1ec686.mov

Logs

======== Exception caught by gesture ===============================================================
The following assertion was thrown while handling a gesture:
'package:flutter/src/widgets/scrollable.dart': Failed assertion: line 875 pos 12: '_hold == null': is not true.


Either the assertion indicates an error in the framework itself, or we should provide substantially more information in this error message to help you determine and fix the underlying cause.
In either case, please report this assertion by filing a bug on GitHub:
  https://github.com/flutter/flutter/issues/new?template=2_bug.yml

When the exception was thrown, this was the stack: 
#2      ScrollableState._handleDragStart (package:flutter/src/widgets/scrollable.dart:875:12)
#3      DragGestureRecognizer._checkStart.<anonymous closure> (package:flutter/src/gestures/monodrag.dart:849:53)
#4      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:357:24)
#5      DragGestureRecognizer._checkStart (package:flutter/src/gestures/monodrag.dart:849:7)
#6      DragGestureRecognizer._checkDrag (package:flutter/src/gestures/monodrag.dart:815:5)
#7      DragGestureRecognizer.acceptGesture (package:flutter/src/gestures/monodrag.dart:743:7)
#8      GestureArenaManager._resolveByDefault (package:flutter/src/gestures/arena.dart:275:25)
#9      GestureArenaManager._tryToResolveArena.<anonymous closure> (package:flutter/src/gestures/arena.dart:255:31)
(elided 4 frames from class _AssertionError and dart:async)
Handler: "onStart"
Recognizer: VerticalDragGestureRecognizer#42451
  start behavior: start
====================================================================================================

======== Exception caught by gesture ===============================================================
The following assertion was thrown while handling a gesture:
'package:flutter/src/widgets/scrollable.dart': Failed assertion: line 880 pos 12: '_hold == null || _drag == null': is not true.


Either the assertion indicates an error in the framework itself, or we should provide substantially more information in this error message to help you determine and fix the underlying cause.
In either case, please report this assertion by filing a bug on GitHub:
  https://github.com/flutter/flutter/issues/new?template=2_bug.yml

When the exception was thrown, this was the stack: 
#2      ScrollableState._handleDragUpdate (package:flutter/src/widgets/scrollable.dart:880:12)
#3      DragGestureRecognizer._checkUpdate.<anonymous closure> (package:flutter/src/gestures/monodrag.dart:868:55)
#4      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:357:24)
#5      DragGestureRecognizer._checkUpdate (package:flutter/src/gestures/monodrag.dart:868:7)
#6      DragGestureRecognizer.handleEvent (package:flutter/src/gestures/monodrag.dart:714:11)
#7      PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:97:12)
#8      PointerRouter._dispatchEventToRoutes.<anonymous closure> (package:flutter/src/gestures/pointer_router.dart:143:9)
#9      _LinkedHashMapMixin.forEach (dart:_compact_hash:763:13)
#10     PointerRouter._dispatchEventToRoutes (package:flutter/src/gestures/pointer_router.dart:141:18)
#11     PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:131:7)
#12     GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:530:19)
#13     GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:499:22)
#14     RendererBinding.dispatchEvent (package:flutter/src/rendering/binding.dart:460:11)
#15     GestureBinding._handlePointerEventImmediately (package:flutter/src/gestures/binding.dart:437:7)
#16     GestureBinding.handlePointerEvent (package:flutter/src/gestures/binding.dart:394:5)
#17     GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:341:7)
#18     GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:308:9)
#19     _invoke1 (dart:ui/hooks.dart:332:13)
#20     PlatformDispatcher._dispatchPointerDataPacket (dart:ui/platform_dispatcher.dart:451:7)
#21     _dispatchPointerDataPacket (dart:ui/hooks.dart:267:31)
(elided 2 frames from class _AssertionError)
Handler: "onUpdate"
Recognizer: VerticalDragGestureRecognizer#42451
  start behavior: start
====================================================================================================

Flutter Doctor output

Doctor output

[✓] Flutter (Channel stable, 3.29.0, on macOS 15.3 24D60 darwin-arm64, locale de-DE) [1.836ms]
    • Flutter version 3.29.0 on channel stable at /Users/***
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 35c388afb5 (4 days ago), 2025-02-10 12:48:41 -0800
    • Engine revision f73bfc4522
    • Dart version 3.7.0
    • DevTools version 2.42.2

#156381 (comment)

The underlying issue is that under the hood we use ScrollPosition.animateTo to snap the nav bar forward or backward when partially scrolled. But if the snap is interrupted mid-animation it throws an exception. This issue explains more.

Thanks for pointing this out. How should we proceed here? I think there is a difference between an error caused by an individual implementation and an issue originating from the framework, where there is no direct way to fix it ourselves. I'm honestly not sure how we should handle this right now. The error was noticed during the review process, yet the pull request was still merged. It's also easy to reproduce and will likely occur more frequently in the future. I don’t have a workaround in mind at the moment, but I haven't examined the implementation in detail yet.

@Zelkreps

@Zelkreps, I added the extra space at the bottom, if the size of the widget is larger than the available phone height, then this issue doesn't happen, it is workaround until the issue is fixed in the framework.

I was able to replicate this on latest sdk versions (stable and master) which triggers the reported error log.

stable : 3.29.0
master : 3.30.0-1.0.pre.191

@itsatifsiddiqui

Hello. I also encountered this problem at Flutter 3.29.0 version.

@Zelkreps, I added the extra space at the bottom, if the size of the widget is larger than the available phone height, then this issue doesn't happen, it is workaround until the issue is fixed in the framework.

Tried this way but it didn't work for me. Can you please provide full code to show your solution?

The solution provided by @itsatifsiddiqui does not address the root cause of the problem and therefore does not work. The reason is addressed here #156381. To resolve this issue without downgrading the version, use CupertinoNavigationBar instead of CupertinoSliverNavigationBar.

Hello. I also encountered this problem at Flutter 3.29.0 version.

@Zelkreps, I added the extra space at the bottom, if the size of the widget is larger than the available phone height, then this issue doesn't happen, it is workaround until the issue is fixed in the framework.

Tried this way but it didn't work for me. Can you please provide full code to show your solution?

The solution provided by @itsatifsiddiqui does not address the root cause of the problem and therefore does not work. The reason is addressed here #156381. To resolve this issue without downgrading the version, use CupertinoNavigationBar instead of CupertinoSliverNavigationBar.

Yes, the solution I provided above doesn't work effectively, but what I have noticed is if there is extra space available then, chances of happening this error is low. After adding the extra space, it was not crashing that often.

I ended up using the ClampingScrollPhysics

CustomScrollView(
      physics: ClampingScrollPhysics(),
      slivers: [
            .
            .
            .
            
            //Other widgets here.
            .
            .
            .
      ],
    );

Otherway around is to add the extra space at the end. Doesn't always work. But in my testing, this error was happening more if extra spacing was not added.

CustomScrollView(
      slivers: [
        SliverList.list(children: [

            .
            .
            .
            
            //Other widgets here.
            .
            .
            .
            SizedBox(height: 500) , /// Adding this extra space reduces the chances of this exception.
          ],
        )
      ],
    );

Fix race condition causing crash when interacting with an animating s…

Hello. I also encountered this problem at Flutter 3.29.0 version.

@Zelkreps, I added the extra space at the bottom, if the size of the widget is larger than the available phone height, then this issue doesn't happen, it is workaround until the issue is fixed in the framework.

Tried this way but it didn't work for me. Can you please provide full code to show your solution?

The solution provided by @itsatifsiddiqui does not address the root cause of the problem and therefore does not work. The reason is addressed here #156381. To resolve this issue without downgrading the version, use CupertinoNavigationBar instead of CupertinoSliverNavigationBar.

Yeah, thank you. Although CupertinoNavigationBar component has a different behavior, it's still good for iOS AppBar style

Fix race condition causing crash when interacting with an animating s…

Even on Flutter 3.30.0-1.0.pre.501 • channel master •
i was still having issue with CustomScrollView and another scroll gridview widget inside it.

can't find error, already downgraded to 3.27.4, issue fixed after that

miss CupertinoNavigationBar.large btw

Fix race condition causing crash when interacting with an animating s…

[CP][Stable] Fix race condition causing crash when interacting with a…

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.

[CP][Stable] Fix race condition causing crash when interacting with a…

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Assertion Error using CustomScrollView with CupertinoSliverNavigationBar (Flutter 3.29) #163297

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Assertion Error using CustomScrollView with CupertinoSliverNavigationBar (Flutter 3.29) #163297

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victorsanni commented on Feb 14, 2025

victorsanni commented on Feb 14, 2025

bobekos commented on Feb 15, 2025

Zelkreps commented on Feb 17, 2025

itsatifsiddiqui commented on Feb 18, 2025

JosephM101 commented on Feb 18, 2025

obenkucuk commented on Feb 19, 2025

darshankawar commented on Feb 19, 2025

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Zelkreps commented on Mar 4, 2025

itsatifsiddiqui commented on Mar 4, 2025

Rollfreeze commented on Mar 5, 2025

andreykuzovlevv commented on Mar 7, 2025

github-actions commented on Mar 21, 2025

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