flutter : Failed assertion: boolean expression must not be null - flutter

Question

i am tried to run my project and this error still appearing
Failed assertion: boolean expression must not be null
i was run it more than 30 times and it was worked but now it doesn't and i don't know the reason for this problem i am not change any thing in my code before the error , and i tried some solutions and it doesn't work also , so what should i do now !
this is my screen which has the problem
class _TourguideDetailesState extends State<TourguideDetailes>
with TickerProviderStateMixin {
AppProvider appProvider;
ScrollController scrollController = ScrollController(initialScrollOffset: 0);
AnimationController animationController;
#override
void initState() {
animationController = AnimationController(
duration: Duration(milliseconds: 2000), vsync: this);
animationController.forward();
super.initState();
}
#override
void dispose() {
animationController.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
appProvider = Provider.of<AppProvider>(context);
return Scaffold(
backgroundColor: AppTheme.getTheme().backgroundColor,
body: Stack(
children: <Widget>[
NestedScrollView(
controller: scrollController,
physics: NeverScrollableScrollPhysics(),
headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
return <Widget>[
SliverPersistentHeader(
pinned: true,
floating: true,
delegate: ContestTabHeader(
(MediaQuery.of(context).size.height),
appProvider.selectedTourguide,
() {
scrollController.animateTo(MediaQuery.of(context).size.height - MediaQuery.of(context).size.height / 5,
duration: Duration(milliseconds: 500), curve: Curves.fastOutSlowIn);
},
getGuideDetails(),
),
),
];
},
body: ListView(
padding: EdgeInsets.only(top: 24),
children: <Widget>[
Padding(
padding: const EdgeInsets.only(left: 24, right: 24),
child: getGuideDetails(isInList: true),
),
Padding(
padding: const EdgeInsets.all(16.0),
child: Divider(
height: 1,
),
),
Padding(
padding: const EdgeInsets.only(left: 24, right: 24),
child: Row(
children: <Widget>[
Expanded(
child: Text(
"Biography",
style: TextStyle(
fontWeight: FontWeight.w600,
fontSize: 18,
letterSpacing: 0.5,
),
),
),
],
),
),
Padding(
padding:
EdgeInsets.only(left: 24, right: 24, top: 4, bottom: 8),
child: Text(
appProvider.selectedTourguide.bio == null
? ""
: appProvider.selectedTourguide.bio,
style: TextStyle(
fontSize: 14,
color: AppTheme.getTheme().disabledColor,
),
)),
Padding(
padding: const EdgeInsets.only(left: 24, right: 24),
child: Row(
children: <Widget>[
Expanded(
child: Text(
"Native Language",
style: TextStyle(
fontWeight: FontWeight.w600,
fontSize: 18,
letterSpacing: 0.5,
),
),
),
],
),
),
Padding(
padding:
EdgeInsets.only(left: 24, right: 24, top: 4, bottom: 8),
child: Text(
appProvider.selectedTourguide.nativeLanguage == null ? "" : appProvider.selectedTourguide.nativeLanguage,
style: TextStyle(
fontSize: 14,
color: AppTheme.getTheme().disabledColor,
),
)),
Padding(
padding:
EdgeInsets.only(left: 24, right: 24, top: 4, bottom: 8),
),
SizedBox(
height: 16,
),
Padding(
padding: const EdgeInsets.only(
left: 16, right: 16, bottom: 16, top: 16),
child: Container(
height: 48,
decoration: BoxDecoration(
color: AppTheme.getTheme().primaryColor,
borderRadius: BorderRadius.all(Radius.circular(24.0)),
boxShadow: <BoxShadow>[
BoxShadow(
color: AppTheme.getTheme().dividerColor,
blurRadius: 8,
offset: Offset(4, 4),
),
],
),
child: Material(
color: Colors.transparent,
child: InkWell(
borderRadius: BorderRadius.all(Radius.circular(24.0)),
highlightColor: Colors.transparent,
onTap: () {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => BookingScreen(
index: appProvider.selectedTourguide,
),
fullscreenDialog: true,
));
},
child: Center(
child: Text(
"Book now",
style: TextStyle(
fontWeight: FontWeight.w500,
fontSize: 16,
color: Colors.white),
),
),
),
),
),
),
SizedBox(
height: MediaQuery.of(context).padding.bottom,
),
],
),
),
Padding(
padding: EdgeInsets.only(top: MediaQuery.of(context).padding.top),
child: Container(
height: AppBar().preferredSize.height,
child: Row(
children: <Widget>[
SizedBox(
height: AppBar().preferredSize.height,
child: Padding(
padding: EdgeInsets.only(top: 8, left: 8),
child: Container(
width: AppBar().preferredSize.height - 8,
height: AppBar().preferredSize.height - 8,
decoration: BoxDecoration(color: AppTheme.getTheme().disabledColor.withOpacity(0.4), shape: BoxShape.circle),
child: Material(
color: Colors.transparent,
child: InkWell(
borderRadius: BorderRadius.all(
Radius.circular(32.0),
),
onTap: () {
if (scrollController.offset != 0.0) {
scrollController.animateTo(0.0, duration: Duration(milliseconds: 500), curve: Curves.easeInOutQuad);
} else {
Navigator.pop(context);
}
},
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Icon(Icons.arrow_back, color: AppTheme.getTheme().backgroundColor),
),
),
),
),
),
),
Expanded(
child: SizedBox(),
),
],
),
),
)
],
),
);
}
Widget getGuideDetails({bool isInList = false}) {
return Row(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.end,
children: <Widget>[
Expanded(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(
appProvider.selectedTourguide.name,
textAlign: TextAlign.left,
style: TextStyle(
fontWeight: FontWeight.w600,
fontSize: 22,
color: isInList == null
? AppTheme.getTheme().textTheme.body1.color
: Colors.white,
),
),
Row(
crossAxisAlignment: CrossAxisAlignment.center,
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
Text(
appProvider.selectedTourguide.address,
style: TextStyle(
fontSize: 14,
color: isInList == null
? AppTheme.getTheme().disabledColor.withOpacity(0.5)
: Colors.white,
),
),
SizedBox(
width: 4,
),
Icon(
FontAwesomeIcons.mapMarkerAlt,
size: 12,
color: AppTheme.getTheme().primaryColor,
),
],
),
isInList == null
? SizedBox()
: Padding(
padding: const EdgeInsets.only(top: 4),
child: Row(
children: <Widget>[
Text(
" ${appProvider.selectedTourguide.review} Reviews",
style: TextStyle(
fontSize: 14,
color: isInList
? AppTheme.getTheme().disabledColor
: Colors.white,
),
),
],
),
),
],
),
),
Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.end,
children: <Widget>[
Row(
children: <Widget>[
Text(
appProvider.selectedTourguide.tariffValue= null ? '' : appProvider.selectedTourguide.tariffValue,
textAlign: TextAlign.left,
style: TextStyle(
fontWeight: FontWeight.w600,
fontSize: 22,
color: isInList == null
? AppTheme.getTheme().textTheme.body1.color
: Colors.white,
),
),
Text(
appProvider.selectedTourguide.currency= null ? '' : appProvider.selectedTourguide.currency,
textAlign: TextAlign.left,
style: TextStyle(
fontWeight: FontWeight.w600,
fontSize: 22,
color: isInList == null
? AppTheme.getTheme().textTheme.body1.color
: Colors.white,
),
),
],
),
Text(
"/per hour",
style: TextStyle(
fontSize: 14,
color: isInList == null
? AppTheme.getTheme().disabledColor.withOpacity(0.5)
: Colors.white,
),
),
],
),
],
);
}
}
class ContestTabHeader extends SliverPersistentHeaderDelegate {
final Widget ui;
final VoidCallback callback;
final TourGuide tourguideData;
final double heightValue;
ContestTabHeader(
this.heightValue,
this.tourguideData,
this.callback,
this.ui,
);
#override
Widget build(BuildContext context, double shrinkOffset, bool overlapsContent) {
var minValue = (shrinkOffset < heightValue - heightValue / 5? shrinkOffset: heightValue / 5);
return Container(
height: heightValue - minValue,
decoration: BoxDecoration(
color: AppTheme.getTheme().primaryColor,
boxShadow: <BoxShadow>[
BoxShadow(
color: AppTheme.getTheme().dividerColor,
blurRadius: 8,
offset: Offset(4, 4),
),
],
),
child: Stack(
alignment: Alignment.bottomCenter,
children: <Widget>[
Positioned(
bottom: 0,
left: 0,
right: 0,
top: 0,
child: Container(
width: MediaQuery.of(context).size.width,
child: Image.network(
tourguideData.photo == null
? 'https://i.ytimg.com/vi/TWaReNkjTLk/maxresdefault.jpg'
: tourguideData.photo,
fit: BoxFit.cover,
),
),
),
Positioned(
bottom: MediaQuery.of(context).padding.bottom + 16,
left: 0,
right: 0,
child: Opacity(
opacity: getOpValue(minValue, heightValue / 5),
child: Column(
children: <Widget>[
Container(
padding: EdgeInsets.only(left: 24, right: 24),
child: ClipRRect(
borderRadius: BorderRadius.all(Radius.circular(24)),
child: new BackdropFilter(
filter:
new ImageFilter.blur(sigmaX: 10.0, sigmaY: 10.0),
child: Container(
color: Colors.black12,
padding: const EdgeInsets.all(4.0),
child: Column(
children: <Widget>[
SizedBox(
height: 4,
),
Padding(
padding: const EdgeInsets.only(
left: 16, right: 16, top: 8),
child: ui,
),
Padding(
padding: const EdgeInsets.only(
left: 16, right: 16, bottom: 16, top: 16),
child: Container(
height: 48,
decoration: BoxDecoration(
color: AppTheme.getTheme().primaryColor,
borderRadius:
BorderRadius.all(Radius.circular(24.0)),
boxShadow: <BoxShadow>[
BoxShadow(
color: AppTheme.getTheme().dividerColor,
blurRadius: 8,
offset: Offset(4, 4),
),
],
),
child: Material(
color: Colors.transparent,
child: InkWell(
borderRadius: BorderRadius.all(
Radius.circular(24.0)),
highlightColor: Colors.transparent,
onTap: () {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) =>
BookingScreen(),
fullscreenDialog: true,
),
);
},
child: Center(
child: Text(
"Book now",
style: TextStyle(
fontWeight: FontWeight.w500,
fontSize: 16,
color: Colors.white),
),
),
),
),
),
),
],
),
),
),
),
),
SizedBox(
height: 16,
),
Center(
child: ClipRRect(
borderRadius: BorderRadius.all(Radius.circular(24)),
child: new BackdropFilter(
filter:
new ImageFilter.blur(sigmaX: 10.0, sigmaY: 10.0),
child: Container(
color: Colors.black12,
child: Material(
color: Colors.transparent,
child: InkWell(
highlightColor: Colors.transparent,
splashColor: AppTheme.getTheme()
.primaryColor
.withOpacity(0.2),
borderRadius:
BorderRadius.all(Radius.circular(38)),
onTap: () {
try {
callback();
} catch (e) {}
},
child: Padding(
padding: const EdgeInsets.only(
left: 16, right: 16, top: 4, bottom: 4),
child: Row(
mainAxisSize: MainAxisSize.min,
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Text(
'More Details',
style: TextStyle(
color: Colors.white,
fontWeight: FontWeight.w600,
),
),
Padding(
padding: const EdgeInsets.only(top: 2),
child: Icon(
Icons.keyboard_arrow_down,
color: Colors.white,
size: 24,
),
)
],
),
),
),
),
),
),
),
),
],
),
),
)
],
),
);
}
double getOpValue(double minValue, double maxValue) {
var data = (1.0 - (minValue / maxValue));
if (data < 0.0) {
return 0.0;
} else if (data >= 0 && data <= 1) {
return data;
} else {
return 1.0;
}
}
#override
double get maxExtent => heightValue;
#override
double get minExtent => heightValue / 5;
#override
bool shouldRebuild(SliverPersistentHeaderDelegate oldDelegate) {
return true;
}
}

Answer 1

Look at the Text Widget, hope it helps. Too lazy to read the whole thing carefully. By the way, you can replace a == null ? 'whatever' : a with a ?? 'whatever'. ?? is equal with if null
Row(
children: <Widget>[
Text(
/// The problem is probably here, missing '='
appProvider.selectedTourguide.tariffValue= null ? '' : appProvider.selectedTourguide.tariffValue,
textAlign: TextAlign.left,
style: TextStyle(
fontWeight: FontWeight.w600,
fontSize: 22,
color: isInList == null
? AppTheme.getTheme().textTheme.body1.color
: Colors.white,
),
),
Text(
/// The problem is probably here, missing '='
appProvider.selectedTourguide.currency= null ? '' : appProvider.selectedTourguide.currency,
textAlign: TextAlign.left,
style: TextStyle(
fontWeight: FontWeight.w600,
fontSize: 22,
color: isInList == null
? AppTheme.getTheme().textTheme.body1.color
: Colors.white,
),
),
],
),