Flutter tried calling data receiver null - flutter

Question

the flutter code below must show a view the problem is that when I run the code and click on the button to view the view index = 1 I get the following error:
The following NoSuchMethodError was thrown during a scheduler
callback: The getter 'data' was called on null. Receiver: null Tried
calling: data
When the exception was thrown, this was the stack:
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:68:5)
#1 ThemeProvider.of (package:animated_theme_switcher/src/theme_provider.dart:27:22)
now the error appears only in the display of this view, what is it due to and how can I solve it?
ChangeView.dart
..
//Function call new view with index=1
void onItemPressed(BuildContext context, {int index}) {
switch (index) {
case 0:
break;
case 1:
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => UserScreen()
));
break;
}
}
..
User.dart
class UserScreen extends StatelessWidget {
#override
Widget build(BuildContext context) {
ScreenUtil.init(context,
height: MediaQuery.of(context).size.height,
width: MediaQuery.of(context).size.width,
allowFontScaling: true);
var profileInfo = Expanded(
child: Column(
children: <Widget>[
Container(
height: kSpacingUnit.w * 10,
width: kSpacingUnit.w * 10,
margin: EdgeInsets.only(top: kSpacingUnit.w * 3),
child: Stack(
children: <Widget>[
CircleAvatar(
radius: kSpacingUnit.w * 5,
backgroundImage: AssetImage('assets/images/avatar.png'),
),
Align(
alignment: Alignment.bottomRight,
child: Container(
height: kSpacingUnit.w * 2.5,
width: kSpacingUnit.w * 2.5,
decoration: BoxDecoration(
color: Theme.of(context).accentColor,
shape: BoxShape.circle,
),
child: Center(
heightFactor: kSpacingUnit.w * 1.5,
widthFactor: kSpacingUnit.w * 1.5,
child: Icon(
LineAwesomeIcons.pen,
color: kDarkPrimaryColor,
size: ScreenUtil().setSp(kSpacingUnit.w * 1.5),
),
),
),
),
],
),
),
SizedBox(height: kSpacingUnit.w * 2),
Text(
'Nicolas Adams',
style: kTitleTextStyle,
),
SizedBox(height: kSpacingUnit.w * 0.5),
Text(
'nicolasadams#gmail.com',
style: kCaptionTextStyle,
),
SizedBox(height: kSpacingUnit.w * 2),
Container(
height: kSpacingUnit.w * 4,
width: kSpacingUnit.w * 20,
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(kSpacingUnit.w * 3),
color: Theme.of(context).accentColor,
),
child: Center(
child: Text(
'Upgrade to PRO',
style: kButtonTextStyle,
),
),
),
],
),
);
var themeSwitcher = ThemeSwitcher(
builder: (context) {
return AnimatedCrossFade(
duration: Duration(milliseconds: 200),
crossFadeState:
ThemeProvider.of(context).brightness == Brightness.dark
? CrossFadeState.showFirst
: CrossFadeState.showSecond,
firstChild: GestureDetector(
onTap: () =>
ThemeSwitcher.of(context).changeTheme(theme: kLightTheme),
child: Icon(
LineAwesomeIcons.sun,
size: ScreenUtil().setSp(kSpacingUnit.w * 3),
),
),
secondChild: GestureDetector(
onTap: () =>
ThemeSwitcher.of(context).changeTheme(theme: kDarkTheme),
child: Icon(
LineAwesomeIcons.moon,
size: ScreenUtil().setSp(kSpacingUnit.w * 3),
),
),
);
},
);
var header = Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
SizedBox(width: kSpacingUnit.w * 3),
Icon(
LineAwesomeIcons.arrow_left,
size: ScreenUtil().setSp(kSpacingUnit.w * 3),
),
profileInfo,
themeSwitcher,
SizedBox(width: kSpacingUnit.w * 3),
],
);
return ThemeSwitchingArea(
child: Builder(
builder: (context) {
return Scaffold(
body: Column(
children: <Widget>[
SizedBox(height: kSpacingUnit.w * 5),
header,
Expanded(
child: ListView(
children: <Widget>[
UserListItem(
icon: LineAwesomeIcons.user_shield,
text: 'Privacy',
),
UserListItem(
icon: LineAwesomeIcons.history,
text: 'Purchase History',
),
UserListItem(
icon: LineAwesomeIcons.question_circle,
text: 'Help & Support',
),
UserListItem(
icon: LineAwesomeIcons.cog,
text: 'Settings',
),
UserListItem(
icon: LineAwesomeIcons.user_plus,
text: 'Invite a Friend',
),
UserListItem(
icon: LineAwesomeIcons.alternate_sign_out,
text: 'Logout',
hasNavigation: false,
),
],
),
)
],
),
);
},
),
);
}
}
UserListItem.dart
class UserListItem extends StatelessWidget {
final IconData icon;
final String text;
final bool hasNavigation;
const UserListItem({
Key key,
this.icon,
this.text,
this.hasNavigation = true,
}) : super(key: key);
#override
Widget build(BuildContext context) {
return Container(
height: kSpacingUnit.w * 5.5,
margin: EdgeInsets.symmetric(
horizontal: kSpacingUnit.w * 4,
).copyWith(
bottom: kSpacingUnit.w * 2,
),
padding: EdgeInsets.symmetric(
horizontal: kSpacingUnit.w * 2,
),
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(kSpacingUnit.w * 3),
color: Theme.of(context).backgroundColor,
),
child: Row(
children: <Widget>[
Icon(
this.icon,
size: kSpacingUnit.w * 2.5,
),
SizedBox(width: kSpacingUnit.w * 1.5),
Text(
this.text,
style: kTitleTextStyle.copyWith(
fontWeight: FontWeight.w500,
),
),
Spacer(),
if (this.hasNavigation)
Icon(
LineAwesomeIcons.angle_right,
size: kSpacingUnit.w * 2.5,
),
],
),
);
}
}

Answer 1

In your UserScreen inside ThemeSwitcher (where you pass the value in crossFadeState) use ThemeProvider like this
ThemeProvider.themeOf(context).brightness == Brightness.dark