Failed assertion in scrollable.dart ('_drag == null': is not true.)

Steps to Reproduce

Just had this happen once when scrolling in the gallery app home screen (Flutter unmodified TOT sycned to cbfed19) with TalkBack on (was scrolling with 2 fingers).
The scroll was not responding and I had this crash in the log.

Couldn't reproduce this again.

Logs

E/flutter ( 3509): [ERROR:topaz/lib/tonic/logging/dart_error.cc(16)] Unhandled exception:
E/flutter ( 3509): 'package:flutter/src/widgets/scrollable.dart': Failed assertion: line 437: '_drag == null': is not true.
E/flutter ( 3509): #0      _AssertionError._doThrowNew (dart:core-patch/dart:core/errors_patch.dart:37)
E/flutter ( 3509): #1      _AssertionError._throwNew (dart:core-patch/dart:core/errors_patch.dart:33)
E/flutter ( 3509): #2      ScrollableState._handleDragDown (package:flutter/src/widgets/scrollable.dart:437)
E/flutter ( 3509): #3      RawGestureDetectorState._handleSemanticsVerticalDragUpdate (package:flutter/src/widgets/gesture_detector.dart:674)
E/flutter ( 3509): #4      RenderSemanticsGestureHandler._performSemanticScrollUp (package:flutter/src/rendering/proxy_box.dart:3129)
E/flutter ( 3509): #5      SemanticsOwner.performAction (package:flutter/src/rendering/semantics.dart:865)
E/flutter ( 3509): #6      BindingBase&SchedulerBinding&GestureBinding&ServicesBinding&RendererBinding._handleSemanticsAction (package:flutter/src/rendering/binding.dart:188)
E/flutter ( 3509): #7      _invoke2 (file:///b/build/slave/Linux_Engine/build/src/flutter/lib/ui/hooks.dart:129)
E/flutter ( 3509): #8      _dispatchSemanticsAction (file:///b/build/slave/Linux_Engine/build/src/flutter/lib/ui/hooks.dart:77)

Run flutter analyze and attach any output of that command also.

Analyzing 1277 files...
No analyzer warnings! (ran in 37.8s; 13 public members lack documentation)

Flutter Doctor

$ flutter doctor
[✓] Flutter (on Linux, locale en_US.UTF-8, channel master)
    • Flutter at /usr/local/google/home/amirha/git/flutter
    • Framework revision cbfed1960f (2 hours ago), 2017-10-25 07:18:09 -0700
    • Engine revision ec19da1c80
    • Tools Dart version 1.25.0-dev.11.0

[✓] Android toolchain - develop for Android devices (Android SDK 26.0.2)
    • Android SDK at /usr/local/google/home/amirha/Android/Sdk
    • Platform android-26, build-tools 26.0.2
    • Java binary at: /usr/local/google/home/amirha/progs/android-studio/jre/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)

[✓] Android Studio (version 2.3)
    • Android Studio at /opt/android-studio-with-blaze-2.3
    • Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)

[✓] Android Studio (version 2.3)
    • Android Studio at /usr/local/google/home/amirha/progs/android-studio
    • Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)

[✓] IntelliJ IDEA Community Edition (version 2017.2)
    • Flutter plugin version 18.0
    • Dart plugin version 172.4155.35

[✓] Connected devices
    • Pixel • FA6890301419 • android-arm • Android 8.1.0 (API 27)

Looks stale. Is this still relevant?

I don't know, it happened once, I guess we can close and re-open if we see it again.

I have the same problem，how to solve it

[✓] Flutter (Channel stable, v1.5.4-hotfix.2, on Mac OS X 10.14.4 18E226, locale zh-Hans-CN)
• Flutter version 1.5.4-hotfix.2 at /Users/hongka-liming/Downloads/flutter
• Framework revision 7a4c334 (7 weeks ago), 2019-04-29 11:05:24 -0700
• Engine revision 52c7a1e
• Dart version 2.3.0 (build 2.3.0-dev.0.5 a1668566e5)

[✓] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
• Android SDK at /Users/hongka-liming/Library/Android/sdk
• Android NDK location not configured (optional; useful for native profiling support)
• Platform android-28, build-tools 28.0.3
• Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1343-b01)
• All Android licenses accepted.

[!] iOS toolchain - develop for iOS devices (Xcode 10.2.1)
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 10.2.1, Build version 10E1001
✗ libimobiledevice and ideviceinstaller are not installed. To install with Brew, run:
brew update
brew install --HEAD usbmuxd
brew link usbmuxd
brew install --HEAD libimobiledevice
brew install ideviceinstaller
✗ ios-deploy not installed. To install:
brew install ios-deploy
✗ Brew can be used to install tools for iOS device development.
Download brew at https://brew.sh/.

[✓] Android Studio (version 3.4)
• Android Studio at /Applications/Android Studio.app/Contents
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• Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1343-b01)

[✓] Connected device (1 available)
• COR AL00 • 6EJ7N18526001222 • android-arm64 • Android 9 (API 28)

I got this problem when inactive the scrollPhysics and touch the component who has this scroll inactivated

StreamBuilder(
            stream: bloc.places,
            initialData: [],
            builder: (context, snapshot) {
              if (snapshot.data == null) return Container();
              return StreamBuilder(
                stream: bloc.scrollable,
                initialData: true,
                builder: (context, scroll) =>
                    SingleChildScrollView(
                      controller: listScroll,
                      physics: scroll.data
                          ? NeverScrollableScrollPhysics()
                          : ClampingScrollPhysics(),
                      child: Column(
                        children: snapshot.data
                            .toList()
                            .map<Widget>((place) => _row(context, place, bloc))
                            .toList(),
                      ),
                    ),
              );
            },
          )

@amirh

@amirh @zoechi still relevant exact same issue with the exact same case as in prev example. It seems that when physics is changing, while scroll was in progress, it doesn't clear prev state of drag and hold

Code

StreamBuilder<double>(
          stream: _heightStream,
          initialData: _height.value,
          builder: (context, snapshot) {
            return Container(
              width: double.infinity,
              height: snapshot.data,
              color: Theme.of(context).canvasColor,
              child: CustomScrollView(
                controller: _scrollController,
                physics: _isOpened ? AlwaysScrollableScrollPhysics() : NeverScrollableScrollPhysics(),
                primary: false,
                slivers: widget.children,
              ),
            );
          }
        )

Exception

════════ Exception caught by gesture ═══════════════════════════════════════════════════════════════
The following assertion was thrown while handling a gesture:
'package:flutter/src/widgets/scrollable.dart': Failed assertion: line 480 pos 12: '_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=BUG.md

When the exception was thrown, this was the stack: 
#2      ScrollableState._handleDragDown (package:flutter/src/widgets/scrollable.dart:480:12)
#3      DragGestureRecognizer._checkDown.<anonymous closure> (package:flutter/src/gestures/monodrag.dart:359:44)
#4      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:182:24)
#5      DragGestureRecognizer._checkDown (package:flutter/src/gestures/monodrag.dart:359:7)
#6      DragGestureRecognizer.addAllowedPointer (package:flutter/src/gestures/monodrag.dart:236:7)
...
Handler: "onDown"
Recognizer: VerticalDragGestureRecognizer#d1f23
  start behavior: start
════════════════════════════════════════════════════════════════════════════════════════════════════

════════ (2) Exception caught by gesture ═══════════════════════════════════════════════════════════
'package:flutter/src/widgets/scrollable.dart': Failed assertion: line 489 pos 12: '_drag == null': is not true.
════════════════════════════════════════════════════════════════════════════════════════════════════

[✓] Flutter (Channel stable, v1.9.1+hotfix.5, on Mac OS X 10.15 19A602, locale
    ru-UA)
 
[✓] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
[✓] Xcode - develop for iOS and macOS (Xcode 11.1)
[✓] Android Studio (version 3.5)
[✓] Connected device (1 available)

• No issues found!

@amirh

@amirh Can we reopen this? I've been having the same issue in a very similar scenario to @TatsuUkraine while developing sliding_up_panel.

@akshathjain

@akshathjain btw, it seems flutter has built in widget that does exact same as your package

@TatsuUkraine

@TatsuUkraine yeah lol, I released my package before that was introduced (although I think that mine provides many more features)

I am seeing the same issue, I recommend that this will be reopened.

Seeing the same issue, recommended reopening this issue

Observing the same issue when attaching a ScrollController to a CustomScrollView widget.

Still having the same issue.

Same issue here

here is a code :

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

void main() {
runApp(MyApplication());
}

class MyApplication extends StatelessWidget {
@override
Widget build(BuildContext context) {
  return MaterialApp(
    home: Scaffold(
      body: TestBody(),
    ),
  );
}
}

class TestBody extends StatelessWidget {


@override
Widget build(BuildContext context) {
  ScrollController scrollController = ScrollController();
  Size screenSize = MediaQuery.of(context).size;
  return NotificationListener(
    onNotification: (Notification notification) {
      print(notification);
      if (notification is UserScrollNotification) {

        if (notification.direction == ScrollDirection.idle) {
          scrollController.animateTo(
            300,
            curve: Curves.ease,
            duration: Duration(milliseconds: 200),
          );
        }
      }
      return false;
    },
    child: ListView.builder(
      controller: scrollController,
      scrollDirection: Axis.vertical,
      itemCount: Colors.primaries.length,
      itemBuilder: (context, index) {
        return Container(
          height: screenSize.width*.3,
          margin: EdgeInsets.all(20),
          color: Colors.primaries[index],
        );
      },
    ),
  );
}
}

this is happing when you are dragging the list and after you released the drag and list scroll went to an idle state (detecting it in notification listener) than if you could start dragging the list again before the scrollController.animateTo method gets invoked you will see the error is happening

So i have found a workaround for my case taht is like this :


      onNotification: (Notification notification) {
        print(notification);
        if (notification is UserScrollNotification &&
            notification.direction == ScrollDirection.idle) {
          isScrollIdle = true;
          Future.delayed(Duration.zero,() {
            if (isScrollIdle == false) return;
            scrollController.animateTo(
              300,
              curve: Curves.ease,
              duration: Duration(milliseconds: 300),
            );
          });
        }
        return false;
      }

i am postponing the scrollController.animateTo until the next frame and meanwhile, I am listnening to the scroll notifications if there was any notification beside an idle state i would change the isScrollIdle to a false and i am executing the scrollController.animateTo if isScrollIdle is true
I'm not sure about this workaround and it needs more investigation but for now, it is working for me

Still having the same problem! Please reopen this issue.

@amirc901

Please reopen this issue, Because I have almost the same code as @amirc901 , this problem still exists.

Flutter 1.22.0 • channel stable • https://github.com/flutter/flutter.git
Framework • revision d408d30 (6 days ago) • 2020-09-29 11:49:17 -0700
Engine • revision 5babba6
Tools • Dart 2.10.0

Any updates?

same issue here, any updates?

animateTo using ScrollController of NestedScrollView has same issue

Same issue here

Resolví el problema gracias a TatsuUkraine.
Efectivamente esto sucede cuando el scroll está en movimiento y se escribe "neverScrollable...".
Para solucionarlo utilicé timers justo antes de activar "neverScrollable...". y usé otro timer justo después de desactivar.

I solved the problem thanks to TatsuUkraine.
Indeed this happens when the scroll is in motion and "neverScrollable ..." is written.
To fix it I used timers just before activating "neverScrollable ...". and I used another timer right after disabling.

same here

I needed to disable scrolling if calendar was expanded and needed enable scrolling ater calendar is minimized so I have found another workaround:

basically on swipe up I am moving list by 2 pixels up and adding if check atEgde

child: Listener(
                    onPointerMove: (PointerMoveEvent details) {
                      if (!_scrollController.position.atEdge &&
                          details.delta.dy < 0 &&
                          _ordersStore.calendarFormat != CalendarFormat.month) {
                        return;
                      }

                      if (_ordersStore.calendarFormat == CalendarFormat.month && _isSwipingUp(details)) {
                        _ordersStore.calendarFormat = CalendarFormat.week;
                        // Moving list up in order to be not atEdge otherways double list scroll error kicks in
                        _scrollController.animateTo(
                          2,
                          curve: Curves.ease,
                          duration: Duration(microseconds: 10),
                        );
                      }
}

also added conditional physics on ListView

physics: _ordersStore.calendarFormat == CalendarFormat.month
                                ? NeverScrollableScrollPhysics()
                                : ClampingScrollPhysics(),

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.

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Failed assertion in scrollable.dart ('_drag == null': is not true.) #12712

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Failed assertion in scrollable.dart ('_drag == null': is not true.) #12712

Description

Steps to Reproduce

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zoechi commented on Dec 3, 2018

amirh commented on Dec 3, 2018

CatEatFishs commented on Jun 17, 2019

alexviquez commented on Oct 9, 2019

TatsuUkraine commented on Oct 21, 2019

akshathjain commented on Jan 23, 2020

TatsuUkraine commented on Jan 23, 2020

akshathjain commented on Jan 23, 2020

yonatann commented on Apr 15, 2020

SouravDatta1995 commented on Jun 30, 2020

8fdafs2 commented on Jul 1, 2020

RaashVision commented on Jul 24, 2020

amirc901 commented on Jul 24, 2020

Flucadetena commented on Sep 19, 2020

gadearaujo commented on Sep 27, 2020

SF-Simon commented on Oct 5, 2020

ivan-pavliuk commented on Oct 14, 2020

albrownwood commented on Nov 14, 2020

jja08111 commented on Dec 14, 2020

mregnauld commented on Jan 10, 2021

Gcii commented on Feb 3, 2021

vytautas-pranskunas- commented on Mar 2, 2021

vytautas-pranskunas- commented on Mar 2, 2021

github-actions commented on Aug 5, 2021

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