我正在尝试创建一个电影详细信息应用程序，这是我的页面到目前为止的代码：
@override
Widget build(BuildContext context) {
return Scaffold(
body: CustomScrollView(
slivers: <Widget>[
SliverAppBar(
expandedHeight: _appBarHeight,
pinned: true,
flexibleSpace: FlexibleSpaceBar(
title: Text(movie.title),
background: Stack(
fit: StackFit.expand,
children: <Widget>[
Hero(
tag: movie.id,
child: Image.network(
movie.posterArtUrl,
fit: BoxFit.cover,
height: _appBarHeight,
))
],
),
),
),
SliverList(
delegate: SliverChildListDelegate(<Widget>[
RatingInfo(movie),
_buildMovieDetails(_movieDetail),
_buildMovieGenreChips(_movieDetail),
]),
)
],
),
);
}
如您所见，此页面主要由两种方法提供支持，_buildMovieDetails()并且_buildMovieGenreChips(). 这_buildMovieDetails()方法工作得很好，运行时不会返回错误。但是，当我运行该_buildMovieGenreChips()方法时会出现问题。此方法如下所示：
Widget _buildMovieGenreChips(MovieDetail movieDetail) {
if (_isLoading) {
return Center(
child: CircularProgressIndicator(),
);
}
else {
print(movieDetail.genres.toString());
}
}
}
在这个时间点，该方法只是注销movieDetail.genres，它是我创建的自定义流派对象的列表（由流派名称的字符串和流派 ID 的 int 组成）。但是，当运行此代码时，我的应用程序崩溃并返回以下堆栈跟踪：
I/flutter ( 9592): [Instance of 'Genre', Instance of 'Genre', Instance of 'Genre', Instance of 'Genre']
I/flutter ( 9592): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter ( 9592): The following assertion was thrown building _ScrollableScope:
I/flutter ( 9592): 'package:flutter/src/widgets/sliver.dart': Failed assertion: line 291 pos 12: 'child != null': is
I/flutter ( 9592): not true.
I/flutter ( 9592):
I/flutter ( 9592): Either the assertion indicates an error in the framework itself, or we should provide substantially
I/flutter ( 9592): more information in this error message to help you determine and fix the underlying cause.
I/flutter ( 9592): In either case, please report this assertion by filing a bug on GitHub:
I/flutter ( 9592): https://github.com/flutter/flutter/issues/new
I/flutter ( 9592):
I/flutter ( 9592): When the exception was thrown, this was the stack:
I/flutter ( 9592): #2 SliverChildListDelegate.build (package:flutter/src/widgets/sliver.dart)
I/flutter ( 9592): #3 SliverMultiBoxAdaptorElement._build.<anonymous closure> (package:flutter/src/widgets/sliver.dart:716:67)
I/flutter ( 9592): #4 _HashMap.putIfAbsent (dart:collection/runtime/libcollection_patch.dart:143:29)
I/flutter ( 9592): #5 SliverMultiBoxAdaptorElement._build (package:flutter/src/widgets/sliver.dart:716:26)
I/flutter ( 9592): #6 SliverMultiBoxAdaptorElement.performRebuild (package:flutter/src/widgets/sliver.dart:702:69)
I/flutter ( 9592): #7 SliverMultiBoxAdaptorElement.update (package:flutter/src/widgets/sliver.dart:671:7)
I/flutter ( 9592): #8 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #9 RenderObjectElement.updateChildren (package:flutter/src/widgets/framework.dart:4371:32)
I/flutter ( 9592): #10 MultiChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4761:17)
I/flutter ( 9592): #11 _ViewportElement.update (package:flutter/src/widgets/viewport.dart:187:11)
I/flutter ( 9592): #12 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #13 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #14 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #15 ProxyElement.update (package:flutter/src/widgets/framework.dart:3901:5)
I/flutter ( 9592): #16 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #17 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4653:14)
I/flutter ( 9592): #18 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #19 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4653:14)
I/flutter ( 9592): #20 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #21 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4653:14)
I/flutter ( 9592): #22 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #23 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4653:14)
I/flutter ( 9592): #24 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #25 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #26 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #27 StatefulElement.update (package:flutter/src/widgets/framework.dart:3791:5)
I/flutter ( 9592): #28 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #29 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4653:14)
I/flutter ( 9592): #30 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #31 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4653:14)
I/flutter ( 9592): #32 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #33 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4653:14)
I/flutter ( 9592): #34 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #35 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4653:14)
I/flutter ( 9592): #36 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #37 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #38 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #39 StatelessElement.update (package:flutter/src/widgets/framework.dart:3694:5)
I/flutter ( 9592): #40 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #41 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #42 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #43 StatefulElement.update (package:flutter/src/widgets/framework.dart:3791:5)
I/flutter ( 9592): #44 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #45 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #46 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #47 StatefulElement.update (package:flutter/src/widgets/framework.dart:3791:5)
I/flutter ( 9592): #48 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #49 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #50 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #51 ProxyElement.update (package:flutter/src/widgets/framework.dart:3901:5)
I/flutter ( 9592): #52 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #53 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #54 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #55 StatelessElement.update (package:flutter/src/widgets/framework.dart:3694:5)
I/flutter ( 9592): #56 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #57 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #58 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #59 ProxyElement.update (package:flutter/src/widgets/framework.dart:3901:5)
I/flutter ( 9592): #60 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #61 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #62 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #63 ProxyElement.update (package:flutter/src/widgets/framework.dart:3901:5)
I/flutter ( 9592): #64 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #65 RenderObjectElement.updateChildren (package:flutter/src/widgets/framework.dart:4371:32)
I/flutter ( 9592): #66 MultiChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4761:17)
I/flutter ( 9592): #67 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #68 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #69 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #70 StatefulElement.update (package:flutter/src/widgets/framework.dart:3791:5)
I/flutter ( 9592): #71 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #72 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #73 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #74 ProxyElement.update (package:flutter/src/widgets/framework.dart:3901:5)
I/flutter ( 9592): #75 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #76 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #77 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #78 StatefulElement.update (package:flutter/src/widgets/framework.dart:3791:5)
I/flutter ( 9592): #79 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #80 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4653:14)
I/flutter ( 9592): #81 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #82 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #83 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #84 StatelessElement.update (package:flutter/src/widgets/framework.dart:3694:5)
I/flutter ( 9592): #85 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #86 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4653:14)
I/flutter ( 9592): #87 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #88 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #89 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #90 StatefulElement.update (package:flutter/src/widgets/framework.dart:3791:5)
I/flutter ( 9592): #91 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #92 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #93 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #94 StatefulElement.update (package:flutter/src/widgets/framework.dart:3791:5)
I/flutter ( 9592): #95 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #96 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #97 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #98 ProxyElement.update (package:flutter/src/widgets/framework.dart:3901:5)
I/flutter ( 9592): #99 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #100 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #101 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #102 ProxyElement.update (package:flutter/src/widgets/framework.dart:3901:5)
I/flutter ( 9592): #103 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #104 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #105 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #106 StatefulElement.update (package:flutter/src/widgets/framework.dart:3791:5)
I/flutter ( 9592): #107 Element.updateChild (package:flutter/src/widgets/framework.dart:2691:15)
I/flutter ( 9592): #108 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3645:16)
I/flutter ( 9592): #109 Element.rebuild (package:flutter/src/widgets/framework.dart:3487:5)
I/flutter ( 9592): #110 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2234:33)
I/flutter ( 9592): #111 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:626:20)
I/flutter ( 9592): #112 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:208:5)
I/flutter ( 9592): #113 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
I/flutter ( 9592): #114 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
I/flutter ( 9592): #115 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5)
I/flutter ( 9592): #116 _invoke (dart:ui/hooks.dart:120:13)
I/flutter ( 9592): #117 _drawFrame (dart:ui/hooks.dart:109:3)
I/flutter ( 9592): (elided 2 frames from class _AssertionError)
I/flutter ( 9592): ════════════════════════════════════════════════════════════════════════════════════════════════════
I/zygote ( 9592): Do partial code cache collection, code=30KB, data=26KB
I/zygote ( 9592): After code cache collection, code=30KB, data=26KB
I/zygote ( 9592): Increasing code cache capacity to 128KB
I/flutter ( 9592): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 4031 pos 14: '_dependents.isEmpty': is not true.
I/flutter ( 9592): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 2232 pos 16: '!_dirtyElements[index]._active || _dirtyElements[index]._debugIsInScope(context)': is not true.
如堆栈跟踪的第一行所示，我的打印语句运行良好，但我的应用程序在此之后立即崩溃，并且似乎 Flutter 的小部件库崩溃了。有没有人遇到过这个问题？