Exception thrown when ScrollPosition pixels != null

[sometime-rock]

Logs

I/flutter (27216): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (27216): The following assertion was thrown while finalizing the widget tree:
I/flutter (27216): 'package:flutter/src/widgets/scroll_position.dart': Failed assertion: line 687 pos 12: 'pixels !=
I/flutter (27216): null': is not true.

[shihaohong]

Could you share some context as to when this is happening? I believe it may be related to #18756, which I'm currently working on a fix for

[shihaohong]

(Also, please follow the guidelines on information to share when submitting issues, it really helps with quickly identifying and solving the issue ^_^)

[no-response]

Without additional information, we are unfortunately not sure how to resolve this issue. We are therefore reluctantly going to close this bug for now. Please don't hesitate to comment on the bug if you have any more information for us; we will reopen it right away!
Thanks for your contribution.

[keronei]

A beginner here.
Had the same issue with an app I have been working on, here is the actual stack trace:

══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════ I/flutter ( 3338): The following assertion was thrown while finalizing the widget tree: I/flutter ( 3338): 'package:flutter/src/widgets/scroll_position.dart': Failed assertion: line 687 pos 12: 'pixels != I/flutter ( 3338): null': is not true. I/flutter ( 3338): Either the assertion indicates an error in the framework itself, or we should provide substantially I/flutter ( 3338): more information in this error message to help you determine and fix the underlying cause. I/flutter ( 3338): In either case, please report this assertion by filing a bug on GitHub: I/flutter ( 3338): https://github.com/flutter/flutter/issues/new?template=BUG.md I/flutter ( 3338): When the exception was thrown, this was the stack: I/flutter ( 3338): #2 ScrollPosition.dispose (package:flutter/src/widgets/scroll_position.dart:687:12) I/flutter ( 3338): #3 ScrollPositionWithSingleContext.dispose (package:flutter/src/widgets/scroll_position_with_single_context.dart:257:11) I/flutter ( 3338): #4 ScrollableState.dispose (package:flutter/src/widgets/scrollable.dart:367:14) I/flutter ( 3338): #5 StatefulElement.unmount (package:flutter/src/widgets/framework.dart:3921:12) I/flutter ( 3338): #6 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1696:13) I/flutter ( 3338): #7 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #8 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #9 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #10 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #11 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #12 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #13 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #14 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #15 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #16 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #17 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #18 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #19 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #20 MultiChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4970:16) I/flutter ( 3338): #21 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #22 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #23 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #24 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #25 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #26 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #27 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #28 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #29 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #30 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #31 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #32 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #33 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #34 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #35 MultiChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4970:16) I/flutter ( 3338): #36 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #37 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #38 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #39 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #40 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #41 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #42 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #43 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #44 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #45 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #46 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #47 SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4869:14) I/flutter ( 3338): #48 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #49 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #50 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #51 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #52 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #53 SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4869:14) I/flutter ( 3338): #54 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #55 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #56 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #57 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #58 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #59 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #60 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #61 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #62 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #63 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #64 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #65 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #66 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #67 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #68 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #69 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #70 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #71 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #72 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #73 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1694:7) I/flutter ( 3338): #74 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3775:14) I/flutter ( 3338): #75 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1692:13) I/flutter ( 3338): #76 ListIterable.forEach (dart:_internal/iterable.dart:39:13) I/flutter ( 3338): #77 _InactiveElements._unmountAll (package:flutter/src/widgets/framework.dart:1705:25) I/flutter ( 3338): #78 BuildOwner.finalizeTree.<anonymous closure> (package:flutter/src/widgets/framework.dart:2363:27) I/flutter ( 3338): #79 BuildOwner.lockState (package:flutter/src/widgets/framework.dart:2195:15) I/flutter ( 3338): #80 BuildOwner.finalizeTree (package:flutter/src/widgets/framework.dart:2362:7) I/flutter ( 3338): #81 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:702:18) I/flutter ( 3338): #82 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:275:5) I/flutter ( 3338): #83 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1012:15) I/flutter ( 3338): #84 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:952:9) I/flutter ( 3338): #85 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.scheduleWarmUpFrame.<anonymous closure> (package:flutter/src/scheduler/binding.dart:773:7) I/flutter ( 3338): #94 _Timer._runTimers (dart:isolate-patch/timer_impl.dart:382:19) I/flutter ( 3338): #95 _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:416:5) I/flutter ( 3338): #96 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:171:12) I/flutter ( 3338): (elided 10 frames from class _AssertionError, package dart:async, and package dart:async-patch) I/flutter ( 3338): ════════════════════════════════════════════════════════════════════════════════════════════════════

The app doesn't crash but this trace is seen from the run console. I filtered the tree from children up and closed on something that did resulted in the crash not happening again.

In my scenario, my app had two events that needed to run during the first launch and marked as complete, this were the introduction pages and location setup. In the main.dart file, I had two variables:

bool isFirstRun = true;
bool isFirstRunIntro = true;

While painting the MaterialApp, I'd do it conditionally:

home: isFirstRunIntro
                ? MySplashScreen()
                : isFirstRun
                    ? StartUp(model: _model) //sets up user location
                    : Scaffold(
                        body: ...

Then on the model, I had a function that persisted the values in sharedprefs and would look up on them by overriding the initState on the same file.
The function getting the values returned something like:
return {'loc' :settings.getBool("hasRun"), 'hasRunIntro' : settings.getBool("hasRunIntro")};
Once the results were in, I'd call another function to update the variables like this:

setUp(Map<String, dynamic> stat) {
  if (stat['loc'] == null) {
    setState(() {
      isFirstRun = true;
    });
  } else {
    setState(() {
      isFirstRun = false;
    });
  }
  if (stat['hasRunIntro'] == null) {
    setState(() {
      isFirstRunIntro = true;
    });
  } else {
    setState(() {
      isFirstRunIntro = false;
    });
  }
}

Assuming that if the app was running for the first time, the values would obviously return null and the next time, it would have a true(Because I did set them to true after every segment was completed->intro & location setup).

I realised that defaulting the values to true(of variables), would mean that every other time the app starts, it would start playing the intro just before the result from sharedprefs arrives, which in my opinion, allowed a short window period that rendered null pixels(in some way) while switching to homepage after realising that the intro should not come to stage - withdrawing it just before it's painted.

My solution was to default the variables to false , then when the results would come in, it would do setState with 'false' results which means there's no windows for null pixels.

I tried to use a FutureBuilder but it seems to take a while to get the results and display while switching tabs, which resulted in a black screen for half a second every time I switch tabs.

In summary, by initialising the variables to true, everything seems to work jus fine.

bool isFirstRun = true;
bool isFirstRunIntro = true;

[github-actions]

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.