Flutter Error: 'indexOf(child) > index': is not true. (StreamBuilder,PageView) - flutter

Question

I'm trying to create a screen that is contained within a pageview, that also contains a page view for part of the screen.
To acheive this I have an unlimited page view for the whole page itself, then every page has a header view, with a bottom half that has a page view with 3 possible options. I have this pretty much working, however, the pages I am using I would like a StreamBuilder... This is where the issue is caused.
class DiaryPage extends StatefulWidget {
#override
State<StatefulWidget> createState() => _DiaryPage();
}
class _DiaryPage extends State<DiaryPage> with TickerProviderStateMixin {
DiaryBloc _diaryBloc;
TabController _tabController;
PageController _pageController;
#override
void initState() {
_diaryBloc = BlocProvider.of<DiaryBloc>(context);
_diaryBloc.init();
_tabController = TabController(length: 3, vsync: this);
_pageController = PageController(initialPage: _diaryBloc.initialPage);
super.initState();
}
#override
void dispose() {
_diaryBloc.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
return Flexible(
child: PageView.builder(
controller: _pageController,
itemBuilder: (BuildContext context, int position) {
return _buildPage(_diaryBloc.getDateFromPosition(position));
},
itemCount: _diaryBloc.amountOfPages,
),
);
}
Widget _buildPage(DateTime date) {
return Column(
mainAxisSize: MainAxisSize.max,
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[_getHeader(date), _getTabBody()],
);
}
Widget _getHeader(DateTime date) {
return Card(
child: SizedBox(
width: double.infinity,
height: 125,
child: Column(
children: <Widget>[
Padding(
padding: const EdgeInsets.fromLTRB(8, 16, 8, 0),
child: Text(
'${DateFormat('EEEE').format(date)} ${date.day} ${DateFormat('MMMM').format(date)}',
style: Theme.of(context).textTheme.subtitle,
textScaleFactor: 1,
textAlign: TextAlign.center,
),
),
Row(
mainAxisSize: MainAxisSize.max,
children: <Widget>[
IconButton(
icon: const Icon(Icons.chevron_left),
onPressed: () => {
_pageController.previousPage(
duration: Duration(milliseconds: 250),
curve: Curves.ease)
},
),
const Expanded(child: LinearProgressIndicator()),
IconButton(
icon: const Icon(Icons.chevron_right),
onPressed: () => {
_pageController.nextPage(
duration: Duration(milliseconds: 250),
curve: Curves.ease)
},
),
],
),
Container(
height: 40.0,
child: DefaultTabController(
length: 3,
child: Scaffold(
backgroundColor: Colors.white,
appBar: TabBar(
controller: _tabController,
unselectedLabelColor: Colors.grey[500],
labelColor: Theme.of(context).primaryColor,
tabs: const <Widget>[
Tab(icon: Icon(Icons.pie_chart)),
Tab(icon: Icon(Icons.fastfood)),
Tab(icon: Icon(Icons.directions_run)),
],
),
),
),
),
],
),
),
);
}
Widget _getTabBody() {
return Expanded(
child: TabBarView(
controller: _tabController,
children: <Widget>[
_getOverviewScreen(),
_getFoodScreen(),
_getExerciseScreen(),
],
),
);
}
// TODO - this seems to be the issue, wtf and why
Widget _getBody() {
return Flexible(
child: StreamBuilder<Widget>(
stream: _diaryBloc.widgetStream,
initialData: _diaryBloc.buildEmptyWidget(),
builder: (BuildContext context, AsyncSnapshot<Widget> snapshot) {
return snapshot.data;
},
),
);
}
Widget _getExerciseScreen() {
return Text("Exercise Screen"); //_getBody();
}
Widget _getFoodScreen() {
return Text("Food Screen"); //_getBody();
}
Widget _getOverviewScreen() {
return _getBody();
}
}
As you can see, there are three widgets being returned as part of the sub page view, 2 of them are Text Widgets which show correctly, but the StreamBuilder, which is populated correctly with another Text Widget seems to give me the red screen of death. Any ideas?

Answer 1

Fixed the problem, it was related to the StreamBuilder being wrapped in a Flexible rather than a column. I then added column to have a mainAxisSize of max... Seemed to work.

Answer 2

For custom ListView/PageView
In my case, I wanted to clear the list of my listview. In a custom ListView/PageView, the findChildIndexCallback will find the element's index after i.e. a reordering operation, but also when you clear the list.
yourList.indexWhere()unfortunately returns -1 when it couldn't find an element. So, Make sure to return null in that case, to tell the callback that the child doesn't exist anymore.
...
findChildIndexCallback: (Key key) {
final ValueKey<String> valueKey = key as ValueKey<String>;
final data = valueKey.value;
final index = images.indexWhere((element) => element.id == data);
//important here:
if (index > 0 ) return index;
else return null;
},