Bug: PageController.page cannot be accessed before a PageView is built with it

[damphat]

Describe the bug
When the IntroductionScreen has been disposed, the async method _autoScroll(int? _durationInt) continues to run asynchronously.

That causes an Exception has occurred.
_AssertionError ('package:flutter/src/widgets/page_view.dart': Failed assertion: line 173 pos 7: 'positions.isNotEmpty': PageController.page cannot be accessed before a PageView is built with it.)

To Reproduce
Run the example of this package with pushReplacement() and showSkipButton = true:

    void _onIntroEnd(context) {
        Navigator.of(context).pushReplacement(
            MaterialPageRoute(builder: (_) => const HomePage()),
        );
    }
    showSkipButton: true,
    showBackButton: false,

To fix this issues _autoScroll process must be canceled in dispose()

[ghenry]

Thanks for your report. Want to send a PR?

[Macacoazul01]

Adding this here to look later, maybe it'll help with the problem.

https://stackoverflow.com/questions/17552757/is-there-any-way-to-cancel-a-dart-future

[Macacoazul01]

@damphat can you test the PR to see if it solves your problem?

[Macacoazul01]

@ghenry are you maintaining dots indicator too?

[ghenry]

Can do :)

…

On Wed, 3 May 2023, 23:43 Gianluca Bettega, ***@***.***> wrote: @ghenry <https://github.com/ghenry> are you maintaining dots indicator too? — Reply to this email directly, view it on GitHub <#175 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AABG66BX623JA6HNHKWOXITXELNP5ANCNFSM6AAAAAAXRGNDVY> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[Macacoazul01]

gonna open a breaking change PR there
There's no point of position being a double if dots are int

[Macacoazul01]

Pyozer/dots_indicator#24

[Macacoazul01]

if this update lands i'm gonna change here to int too

[damphat]

The last fix does not work; it should be simple as if (!mounted) break;

Make sure to put the statement after the async gap.

        await Future.delayed(_duration);
        if (!mounted) {
          break;
        }

[damphat]

Adding this here to look later, maybe it'll help with the problem.

https://stackoverflow.com/questions/17552757/is-there-any-way-to-cancel-a-dart-future

It seems that we can cancel the return value, but the async code still runs

[Macacoazul01]

The last fix does not work; it should be simple as if (!mounted) break;

Make sure to put the statement after the async gap.

        await Future.delayed(_duration);
        if (!mounted) {
          break;
        }

I thought of using mounted property instead of the cancel one, but wanna try the cancel for the first time. Unfortunately it didnt work...

Tks for the help!

When @ghenry approves the PR this will be fixed

[ghenry]

Approved and merged. Just awaiting perms for pub.dev.

[erixsyaiful]

is this bug not resolved yet? i still got the same bug in version 3.1.9

[damphat]

is this bug not resolved yet? i still got the same bug in version 3.1.9

@Macacoazul01 The bug has reappeared in the implementation of infinityAutoScroll. Did you forget to check if the widget is still mounted after the async gaps?

f25bbbd#diff-b01e1c7007799dbc6e79576c5c970152638818840b6e2e6e630f352ee545321c

[Macacoazul01]

[damphat]

Hi, you have moved the async gap with (await Future.delayed(...)) here:

we must check if widget state is still mounted.

The bug is here, when the thread wake up from await Future.delayed(...) it can't touch _pageController because that has been dispose by user.