Exception while scrolling through TabBar navigation

[sahil311289]

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flutter: ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
flutter: The following assertion was thrown while finalizing the widget tree:
flutter: 'package:flutter/src/widgets/scroll_position.dart': Failed assertion: line 657 pos 12: 'pixels !=
flutter: null': is not true.
flutter:
flutter: Either the assertion indicates an error in the framework itself, or we should provide substantially
flutter: more information in this error message to help you determine and fix the underlying cause.
flutter: In either case, please report this assertion by filing a bug on GitHub:
flutter:   https://github.com/flutter/flutter/issues/new
flutter:
flutter: When the exception was thrown, this was the stack:
flutter: #2      ScrollPosition.dispose (package:flutter/src/widgets/scroll_position.dart)
flutter: #3      ScrollPositionWithSingleContext.dispose (package:flutter/src/widgets/scroll_position_with_single_context.dart:255:11)
flutter: #4      ScrollableState.dispose (package:flutter/src/widgets/scrollable.dart:324:14)
flutter: #5      StatefulElement.unmount (package:flutter/src/widgets/framework.dart:3821:12)
flutter: #6      _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1697:13)
flutter: #7      _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #8      ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #9      _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #10     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #11     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #12     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #13     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #14     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #15     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #16     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #17     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #18     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #19     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #20     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #21     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #22     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #23     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #24     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #25     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #26     MultiChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4742:16)
flutter: #27     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #28     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #29     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #30     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #31     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #32     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #33     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #34     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #35     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #36     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #37     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #38     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #39     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #40     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #41     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #42     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #43     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #44     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #45     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #46     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #47     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #48     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #49     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #50     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #51     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #52     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #53     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #54     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #55     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #56     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #57     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #58     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #59     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #60     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #61     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #62     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #63     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #64     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #65     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #66     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #67     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #68     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #69     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #70     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #71     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #72     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #73     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #74     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #75     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #76     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #77     MultiChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4742:16)
flutter: #78     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #79     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #80     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #81     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #82     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #83     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #84     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #85     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #86     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #87     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #88     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #89     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #90     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #91     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #92     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #93     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #94     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #95     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #96     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #97     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #98     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #99     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #100    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #101    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #102    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #103    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #104    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #105    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #106    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #107    SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #108    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #109    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #110    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #111    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #112    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #113    SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #114    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #115    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #116    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #117    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #118    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #119    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #120    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #121    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #122    SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #123    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #124    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #125    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #126    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #127    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #128    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #129    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #130    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #131    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #132    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #133    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #134    MultiChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4742:16)
flutter: #135    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #136    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #137    _TheatreElement.visitChildren (package:flutter/src/widgets/overlay.dart:465:14)
flutter: #138    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #139    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #140    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #141    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #142    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #143    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #144    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #145    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #146    SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #147    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #148    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #149    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #150    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #151    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #152    SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #153    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #154    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #155    SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #156    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #157    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #158    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #159    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #160    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #161    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #162    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #163    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #164    SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #165    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #166    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #167    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #168    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #169    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #170    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #171    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #172    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #173    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #174    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #175    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #176    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #177    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #178    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #179    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #180    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #181    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #182    SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #183    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #184    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #185    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #186    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #187    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #188    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #189    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #190    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #191    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #192    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #193    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #194    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #195    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #196    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #197    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #198    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #199    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #200    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #201    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #202    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #203    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #204    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #205    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #206    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #207    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #208    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #209    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #210    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #211    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #212    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #213    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #214    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #215    SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
flutter: #216    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #217    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #218    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #219    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #220    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #221    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #222    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #223    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
flutter: #224    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
flutter: #225    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
flutter: #226    ListIterable.forEach (dart:_internal/iterable.dart:39:13)
flutter: #227    _InactiveElements._unmountAll (package:flutter/src/widgets/framework.dart:1706:25)
flutter: #228    BuildOwner.finalizeTree.<anonymous closure> (package:flutter/src/widgets/framework.dart:2328:27)
flutter: #229    BuildOwner.lockState (package:flutter/src/widgets/framework.dart:2160:15)
flutter: #230    BuildOwner.finalizeTree (package:flutter/src/widgets/framework.dart:2327:7)
flutter: #231    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:628:18)
flutter: #232    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:208:5)
flutter: #233    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
flutter: #234    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
flutter: #235    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5)
flutter: #236    _invoke (dart:ui/hooks.dart:120:13)
flutter: #237    _drawFrame (dart:ui/hooks.dart:109:3)
flutter: (elided 2 frames from class _AssertionError)
flutter: ════════════════════════════════════════════════════════════════════════════════════════════════════

[escamoteur]

Please add your flutter doctor -v output

seems to be the same as #18763

[ajinasokan]

I have the same issue. Heres my flutter doctor output:

[✓] Flutter (Channel beta, v0.5.1, on Mac OS X 10.13.3 17D102, locale en-IN)
    • Flutter version 0.5.1 at /Users/ajinasokan/flutter
    • Framework revision c7ea3ca377 (4 weeks ago), 2018-05-29 21:07:33 +0200
    • Engine revision 1ed25ca7b7
    • Dart version 2.0.0-dev.58.0.flutter-f981f09760

[✓] Android toolchain - develop for Android devices (Android SDK 27.0.3)
    • Android SDK at /Users/ajinasokan/Library/Android/sdk
    • Android NDK at /Users/ajinasokan/Library/Android/sdk/ndk-bundle
    • Platform android-27, build-tools 27.0.3
    • ANDROID_HOME = /Users/ajinasokan/Library/Android/sdk
    • 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-1024-b01)
    • All Android licenses accepted.

[✓] iOS toolchain - develop for iOS devices (Xcode 9.2)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 9.2, Build version 9C40b
    • ios-deploy 1.9.2
    • CocoaPods version 1.5.2

[✓] Android Studio (version 3.1)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin version 25.0.1
    • Dart plugin version 173.4700
    • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b01)

[✓] VS Code (version 1.24.1)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 2.12.2

[✓] Connected devices (1 available)
    • iPhone 6 • 25B46C9F-DB64-460B-9108-F85437197F3D • ios • iOS 11.2 (simulator)

• No issues found!

[sahil311289]

Issue appears when I click on a TabBar (bottomNavigationBar with a child as TabBar in this case) in a random sequence. Sequentially clicking has no issues. But if I click 3rd tab after clicking 6th, it gives an exception. I hope the screenshot's message is helpful.

[escamoteur]

Please add your flutter doctor -v output, the code of this page fenced in ```Dart above and ``` below the code and the output of the debug view when this exception occurs, Thanks

[sahil311289]

Launching lib/main.dart on LG D802 in debug mode...
Initializing gradle...
Resolving dependencies...
Running 'gradlew assembleDebug'...
registerResGeneratingTask is deprecated, use registerGeneratedFolders(FileCollection)
registerResGeneratingTask is deprecated, use registerGeneratedFolders(FileCollection)
registerResGeneratingTask is deprecated, use registerGeneratedFolders(FileCollection)
Warning: Missing asset in fonts for BadScript
Warning: Missing asset in fonts for Roboto
Warning: Missing asset in fonts for Roboto
Built build/app/outputs/apk/debug/app-debug.apk.
Installing build/app/outputs/apk/app.apk...
I/FlutterActivityDelegate( 5478): onResume setting current activity to this
Warning: Missing asset in fonts for BadScript
Warning: Missing asset in fonts for Roboto
Warning: Missing asset in fonts for Roboto
Syncing files to device LG D802...
W/ResourcesManager( 5478): Asset path '/system/framework/com.android.media.remotedisplay.jar' does not exist or contains no resources.
W/ResourcesManager( 5478): Asset path '/system/framework/com.android.location.provider.jar' does not exist or contains no resources.
V/NativeCrypto( 5478): Registering com/google/android/gms/org/conscrypt/NativeCrypto's 280 native methods...
I/art     ( 5478): Rejecting re-init on previously-failed class java.lang.Class<com.google.android.gms.org.conscrypt.Java7ExtendedSSLSession>
I/art     ( 5478): Rejecting re-init on previously-failed class java.lang.Class<com.google.android.gms.org.conscrypt.Java7ExtendedSSLSession>
I/art     ( 5478): Rejecting re-init on previously-failed class java.lang.Class<com.google.android.gms.org.conscrypt.Java8ExtendedSSLSession>
I/art     ( 5478): Rejecting re-init on previously-failed class java.lang.Class<com.google.android.gms.org.conscrypt.Java8ExtendedSSLSession>
W/System  ( 5478): Could not create com.google.android.gms.org.conscrypt.OpenSSLSocketFactoryImpl with ClassLoader dalvik.system.PathClassLoader[DexPathList[[zip file "/data/app/chat.gabhub.GabHub-2/base.apk"],nativeLibraryDirectories=[/data/app/chat.gabhub.GabHub-2/lib/arm, /vendor/lib, /system/lib]]]: com.google.android.gms.org.conscrypt.OpenSSLSocketFactoryImpl
I/ProviderInstaller( 5478): Installed default security provider GmsCore_OpenSSL
D/libc-netbsd( 5478): [getaddrinfo]: hostname=xxxxx; servname=(null); cache_mode=(null), netid=0; mark=0
D/libc-netbsd( 5478): [getaddrinfo]: ai_addrlen=0; ai_canonname=xxxxx; ai_flags=4; ai_family=0
D/libc-netbsd( 5478): [getaddrinfo]: hostname=xxxxx; servname=(null); cache_mode=(null), netid=0; mark=0
D/libc-netbsd( 5478): [getaddrinfo]: ai_addrlen=0; ai_canonname=xxxxx; ai_flags=1024; ai_family=0
I/System.out( 5478): propertyValue:false
D/libc-netbsd( 5478): [getaddrinfo]: hostname=xxxxx; servname=(null); cache_mode=(null), netid=0; mark=0
D/libc-netbsd( 5478): [getaddrinfo]: ai_addrlen=0; ai_canonname=xxxxx; ai_flags=4; ai_family=0
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/flutter ( 5478): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter ( 5478): The following assertion was thrown while finalizing the widget tree:
I/flutter ( 5478): 'package:flutter/src/widgets/scroll_position.dart': Failed assertion: line 657 pos 12: 'pixels !=
I/flutter ( 5478): null': is not true.
I/flutter ( 5478): Either the assertion indicates an error in the framework itself, or we should provide substantially
I/flutter ( 5478): more information in this error message to help you determine and fix the underlying cause.
I/flutter ( 5478): In either case, please report this assertion by filing a bug on GitHub:
I/flutter ( 5478):   https://github.com/flutter/flutter/issues/new
I/flutter ( 5478): When the exception was thrown, this was the stack:
I/flutter ( 5478): #2      ScrollPosition.dispose (package:flutter/src/widgets/scroll_position.dart)
I/flutter ( 5478): #3      ScrollPositionWithSingleContext.dispose (package:flutter/src/widgets/scroll_position_with_single_context.dart:255:11)
I/flutter ( 5478): #4      ScrollableState.dispose (package:flutter/src/widgets/scrollable.dart:324:14)
I/flutter ( 5478): #5      StatefulElement.unmount (package:flutter/src/widgets/framework.dart:3821:12)
I/flutter ( 5478): #6      _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1697:13)
I/flutter ( 5478): #7      _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #8      ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #9      _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #10     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #11     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #12     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #13     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #14     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #15     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #16     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #17     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #18     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #19     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #20     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #21     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #22     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #23     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #24     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #25     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #26     MultiChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4742:16)
I/flutter ( 5478): #27     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #28     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #29     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #30     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #31     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #32     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #33     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #34     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #35     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #36     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #37     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #38     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
I/flutter ( 5478): #39     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #40     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #41     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #42     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #43     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #44     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
I/flutter ( 5478): #45     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #46     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #47     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #48     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #49     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #50     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #51     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #52     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #53     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #54     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #55     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #56     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #57     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #58     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #59     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #60     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #61     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #62     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #63     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #64     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #65     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #66     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #67     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #68     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #69     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #70     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #71     MultiChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4742:16)
I/flutter ( 5478): #72     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #73     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #74     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #75     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #76     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #77     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #78     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #79     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #80     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #81     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #82     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #83     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
I/flutter ( 5478): #84     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #85     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #86     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #87     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #88     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #89     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
I/flutter ( 5478): #90     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #91     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #92     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #93     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #94     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #95     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #96     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #97     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #98     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #99     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #100    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #101    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #102    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #103    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #104    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #105    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #106    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #107    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #108    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #109    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #110    SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4642:14)
I/flutter ( 5478): #111    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #112    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #113    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #114    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #115    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #116    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #117    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #118    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter ( 5478): #119    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter ( 5478): #120    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter ( 5478): #121    ListIterable.forEach (dart:_internal/iterable.dart:39:13)
I/flutter ( 5478): #122    _InactiveElements._unmountAll (package:flutter/src/widgets/framework.dart:1706:25)
I/flutter ( 5478): #123    BuildOwner.finalizeTree.<anonymous closure> (package:flutter/src/widgets/framework.dart:2328:27)
I/flutter ( 5478): #124    BuildOwner.lockState (package:flutter/src/widgets/framework.dart:2160:15)
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/flutter ( 5478): #125    BuildOwner.finalizeTree (package:flutter/src/widgets/framework.dart:2327:7)
I/flutter ( 5478): #126    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:628:18)
I/flutter ( 5478): #127    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:208:5)
I/flutter ( 5478): #128    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
I/flutter ( 5478): #129    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
I/flutter ( 5478): #130    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5)
I/flutter ( 5478): #131    _invoke (dart:ui/hooks.dart:120:13)
I/flutter ( 5478): #132    _drawFrame (dart:ui/hooks.dart:109:3)
I/flutter ( 5478): (elided 2 frames from class _AssertionError)
I/flutter ( 5478): ════════════════════════════════════════════════════════════════════════════════════════════════════
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/widgets/scroll_position.dart': Failed assertion: line 657 pos 12: 'pixels != null': is not true.
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/widgets/scroll_position.dart': Failed assertion: line 657 pos 12: 'pixels != null': is not true.
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/widgets/scroll_position.dart': Failed assertion: line 657 pos 12: 'pixels != null': is not true.
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/ViewRootImpl( 5478): ViewRoot's KeyEvent { action=ACTION_DOWN, keyCode=KEYCODE_BACK, scanCode=0, metaState=0, flags=0x48, repeatCount=0, eventTime=250143550, downTime=250143550, deviceId=-1, source=0x101 } to com.android.internal.policy.impl.PhoneWindow$DecorView{25d05e4b V.E..... R.....I. 0,0-1080,1920}
I/ViewRootImpl( 5478): ViewRoot's KeyEvent { action=ACTION_UP, keyCode=KEYCODE_BACK, scanCode=0, metaState=0, flags=0x48, repeatCount=0, eventTime=250143627, downTime=250143550, deviceId=-1, source=0x101 } to com.android.internal.policy.impl.PhoneWindow$DecorView{25d05e4b V.E..... R.....I. 0,0-1080,1920}
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_DOWN
I/ViewRootImpl( 5478): ViewRoot's Touch Event : ACTION_UP
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/rendering/object.dart': Failed assertion: line 2775 pos 14: '_debugUltimatePreviousSiblingOf(after, equals: _firstChild)': is not true.
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/rendering/object.dart': Failed assertion: line 2775 pos 14: '_debugUltimatePreviousSiblingOf(after, equals: _firstChild)': is not true.
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/rendering/object.dart': Failed assertion: line 2775 pos 14: '_debugUltimatePreviousSiblingOf(after, equals: _firstChild)': is not true.
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/rendering/object.dart': Failed assertion: line 2775 pos 14: '_debugUltimatePreviousSiblingOf(after, equals: _firstChild)': is not true.
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3497 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3497 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3497 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3497 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3497 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3497 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3497 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3497 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
I/flutter ( 5478): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3497 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
I/flutter ( 5478): Another exception was thrown: The _ScaffoldLayout custom multichild layout delegate forgot to lay out the following children:

[sahil311289]

/Users/sahil/flutterDevelopment/flutter/bin/flutter --no-color doctor
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel beta, v0.5.1, on Mac OS X 10.13.5 17F77, locale en-IN)
[!] Android toolchain - develop for Android devices (Android SDK 28.0.0-rc1)
    ✗ Android license status unknown.
[✓] iOS toolchain - develop for iOS devices (Xcode 9.4.1)
[✓] Android Studio (version 3.1)
[✓] IntelliJ IDEA Community Edition (version 2018.1.5)
[✓] VS Code (version 1.23.1)
[✓] Connected devices (1 available)

! Doctor found issues in 1 category.

[sahil311289]

import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart';
import 'bottom_navigation.dart';
import 'theme.dart';
import 'register.dart';

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'GabHub',
      theme: defaultTargetPlatform == TargetPlatform.android ? tealTheme
          : iOSTheme,
      home: new BottomNavBar(),
    );
  }
}

[sahil311289]

import 'package:flutter/material.dart';
import 'live_chat_tab_base.dart';
import 'posts_tab_base.dart';
import 'events_tab_base.dart';
import 'universities_tab_base.dart';
import 'notifications_tab_base.dart';
import 'profile_tab_base.dart';

class BottomNavBar extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      body: new BottomNav(),
    );
  }
}

class BottomNav extends StatefulWidget {
  @override
  _State createState() => _State();
}

class _State extends State<BottomNav> with SingleTickerProviderStateMixin {
  TabController bottomNavTabController;

  @override
  void initState() {
    super.initState();
    bottomNavTabController = new TabController(length: 6, vsync: this);
  }

  @override
  void dispose() {
    bottomNavTabController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      bottomNavigationBar: new Material(
        color: Theme.of(context).platform == TargetPlatform.android
            ? Theme.of(context).primaryColor
            : Theme.of(context).primaryColor.withOpacity(0.7),
        child: new TabBar(
          indicatorColor: Theme.of(context).accentColor,
          controller: bottomNavTabController,
          tabs: <Widget>[
            new Tab(
              icon: new Icon(Icons.edit, color: Theme.of(context).splashColor),
            ),
            new Tab(
              icon: new Icon(Icons.question_answer,
                  color: Theme.of(context).splashColor),
            ),
            new Tab(
              icon: new Icon(Icons.event_note,
                  color: Theme.of(context).splashColor),
            ),
            new Tab(
              icon: new Icon(Icons.account_balance,
                  color: Theme.of(context).splashColor),
            ),
            new Tab(
              icon: new Icon(Icons.notifications_active,
                  color: Theme.of(context).splashColor),
            ),
            new Tab(
              icon:
                  new Icon(Icons.person, color: Theme.of(context).splashColor),
            ),
          ],
        ),
      ),
      body: new TabBarView(
        children: <Widget>[
          new LiveChatTabBase(),
          new PostsTabBase(),
          new EventsTabBase("Events"),
          new UniversitiesTabBase("Universities"),
          new NotificationsTabBase("Notifications"),
          new ProfileTabBase("Profile"),
        ],
        controller: bottomNavTabController,
      ),
    );
  }
}

[sahil311289]

import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:flutter/cupertino.dart';
import 'dart:math';
import 'package:cloud_firestore/cloud_firestore.dart';

const jsonCodec = const JsonCodec();

class LiveChatTabBase extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      body: new ChatScreen(),
    );
  }
}

class ChatScreen extends StatefulWidget {
  @override
  State createState() => new ChatScreenState();
}

class ChatScreenState extends State<ChatScreen> with TickerProviderStateMixin {
  final List<ChatMessage> _messages = <ChatMessage>[];
  final TextEditingController _textController = new TextEditingController();
  bool _isComposing = false;

  @override
  void dispose() {
    for (ChatMessage message in _messages)
      message.animationController.dispose();
    super.dispose();
  }

  Widget _buildTextComposer() {
    return new IconTheme(
      data: new IconThemeData(
        color: Theme.of(context).accentColor,
      ),
      child: new Column(
        mainAxisSize: MainAxisSize.max,
        mainAxisAlignment: MainAxisAlignment.end,
        children: <Widget>[
          new Row(
            children: <Widget>[
              new Container(
                margin: new EdgeInsets.only(
                  left: 5.0,
                ),
                child: new IconButton(
                  icon: new Icon(
                    Icons.add_circle,
                    color: Colors.black87,
                    size: 28.0,
                  ),
                  onPressed: () => _handleAddContent(),
                ),
              ),
              new Flexible(
                child: Padding(
                  padding: new EdgeInsets.only(
                    left: 5.0,
                  ),
                  child: new TextField(
                    controller: _textController,
                    maxLines: null,
//                    maxLength: 2000,
                    onChanged: (String text) {
                      setState(() {
                        _isComposing = text.replaceAll(" ", "").length > 0;
                      });
                    },
                    decoration: new InputDecoration.collapsed(
                      hintText: "Write a message",
                      hintStyle: new TextStyle(
                        color: Colors.black87,
                      ),
                    ),
                    style: new TextStyle(
                      color: Colors.black87,
                      fontSize: 17.0,
                    ),
//                    onChanged: () => _valueChanged(_textController.text),
                  ),
                ),
              ),
              new Container(
                margin: new EdgeInsets.only(
                  right: 5.0,
                ),
                child: _isComposing
                    ? Theme.of(context).platform == TargetPlatform.android
                        ? new IconButton(
                            icon: new Icon(
                              Icons.send,
                              color: Colors.black87,
                              size: 28.0,
                            ),
                            onPressed: () =>
                                _handleSubmitted(_textController.text),
                          )
                        : new CupertinoButton(
                            child: new Text('Send'),
                            onPressed: () =>
                                _handleSubmitted(_textController.text),
                          )
                    : new IconButton(
                        icon: new Icon(
                          Icons.keyboard_voice,
                          color: Colors.black87,
                          size: 28.0,
                        ),
                        onPressed: () => _handleVoiceInput(),
                      ),
              ),
            ],
          ),
        ],
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      backgroundColor: Theme.of(context).backgroundColor,
      appBar: new AppBar(
        backgroundColor: Theme.of(context).primaryColor,
        title: new Text(
          'Live chat',
          style: new TextStyle(color: Theme.of(context).hintColor),
        ),
        elevation:
            Theme.of(context).platform == TargetPlatform.android ? 4.0 : 0.0,
      ),
      body: new Container(
          child: new Column(
            children: <Widget>[
              new Flexible(
                child:
//                new ListView.builder(
//                  padding: new EdgeInsets.all(8.0),
//                  reverse: true,
//                  itemBuilder: (_, int index) => _messages[index],
//                  itemCount: _messages.length,
//                ),

                    new StreamBuilder(
                  stream:
                      Firestore.instance.collection('live_chat').snapshots(),
                  builder: (context, snapshot) {
                    if (!snapshot.hasData) return const Text('Loading...');

                    return new ListView.builder(
                      itemCount: snapshot.data.documents.length,
                      padding: const EdgeInsets.all(8.0),
                      reverse: true,
                      itemExtent: 55.0,
                      itemBuilder: (context, index) {
                        DocumentSnapshot ds = snapshot.data.documents[index];
                        return new Text(
                          " ${ds['message']}",
                          style: TextStyle(color: Colors.white70),
                        );
                      },
                    );
                  },
                ),
              ),
              new Divider(
                height: 1.0,
              ),
              new Container(
                decoration: new BoxDecoration(
                  color: Theme.of(context).cardColor, //Colors.white70,
                ),
                child: _buildTextComposer(),
              ),
            ],
          ),
          decoration: Theme.of(context).platform == TargetPlatform.iOS
              ? new BoxDecoration(
                  border: new Border(
                    top: new BorderSide(color: Colors.grey[200]),
                  ),
                )
              : null),
    );
  }

  void _handleSubmitted(String text) {
    _textController.clear();
    setState(() {
      _isComposing = false;
    });

    // TODO: Change color to a color based on email id so that every person's color remains constant
    final String username = "sahilwad";
    List<int> ints = username.codeUnits;
    var range = new Random();

    ChatMessage message = new ChatMessage(
      text,
      ints[5] + ints[6],
      ints[2],
      ints[1] + ints[0],
      ints[3] + ints[4],
      new AnimationController(
        duration: new Duration(milliseconds: 400),
        vsync: this,
      ),
    );
    setState(() {
      _messages.insert(0, message);
    });
    message.animationController.forward();
  }

  _handleVoiceInput() {
    print('Voice input method');
  }

  _handleAddContent() {
    print('Add content clicked');
  }
}

class ChatMessage extends StatelessWidget {
  final String text;
  final int colorA;
  final int colorR;
  final int colorG;
  final int colorB;
  final AnimationController animationController;

  ChatMessage(this.text, this.colorA, this.colorR, this.colorG, this.colorB,
      this.animationController);

  @override
  Widget build(BuildContext context) {
    return new SizeTransition(
      sizeFactor: new CurvedAnimation(
        parent: animationController,
        curve: Curves.easeOut,
      ),
      axisAlignment: 0.0,
      child: new Container(
        margin: const EdgeInsets.symmetric(vertical: 7.0),
        child: new Row(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: <Widget>[
            new Container(
              margin: const EdgeInsets.only(
                right: 10.0,
              ),
              child: new Padding(
                padding: new EdgeInsets.only(top: 12.0),
                child: new CircleAvatar(
                  maxRadius: 13.0,
                  backgroundColor:
                      Color.fromARGB(colorA, colorR, colorG, colorB),
                ),
              ),
            ),
            new Expanded(
              child: new Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: <Widget>[
                  new Row(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: <Widget>[
                      new Padding(
                        padding: new EdgeInsets.only(
                          bottom: 4.0,
                          right: 35.0,
                        ),
                        child: new Text(
                          '25 June 2018, 4:11 am',
                          style: new TextStyle(
                            color: Theme.of(context).platform ==
                                    TargetPlatform.android
                                ? Colors.white70
                                : Colors.black54,
                            fontSize: 12.0,
                            letterSpacing: 0.6,
                          ),
                        ),
                      ),
                    ],
                  ),
                  new Container(
                    width: 300.0,
                    child: new Text(
                      text,
                      style: new TextStyle(
                        color:
                            Theme.of(context).platform == TargetPlatform.android
                                ? Colors.white
                                : Colors.black87,
                        letterSpacing: 0.4,
                      ),
                    ),
                  ),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }
}

[sahil311289]

import 'package:flutter/material.dart';

class NotificationsTabBase extends StatelessWidget {
  final String title;

  NotificationsTabBase(this.title);

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      backgroundColor: Theme.of(context).backgroundColor,
      appBar: new AppBar(
        title: new Text(
          title,
          style: new TextStyle(
            color: Theme.of(context).hintColor,
          ),
        ),
        elevation:
            Theme.of(context).platform == TargetPlatform.android ? 4.0 : 0.0,
        backgroundColor: Theme.of(context).primaryColor,
      ),
      body: new Container(
          child: new Center(
            child: new Text(title),
          ),
          decoration: Theme.of(context).platform == TargetPlatform.iOS
              ? new BoxDecoration(
                  border: new Border(
                    top: new BorderSide(color: Colors.grey[200]),
                  ),
                )
              : null),
    );
  }
}

[sahil311289]

1. If I comment using the live_chat tab and click on notification tab, the code breaks!
2. Typing in a TextField gets me only white space once the keyboard is up. I've seen threads for non-TabBar pages and they are still manageable but while in a TabBar, Android still gives you the option of Back icon which closes the keyboard so I was able to post content. While in iOS once the keyboard is up, I have white screen and nothing else to do since there is no back button.

Also, you may not be able to see but I have top level TabBar within Bottom TabBar on some tabs. So it's a complex structure. Please help!

As much as I wanted to keep the code private, I guess there is no other option. I have a private repo on GitHub.