How can I Initialize provider? - flutter

Question

I have implemented Provider for state management in my app. Now, I need to add some data in the class once the screen is loaded.
How I can achieve this?
stepInfo.addToList = new VaccStep(); // Need to call it one time once screen is loaded.
I have tried to call this method from initState but it's giving error!!
class AdminAddVaccination extends StatefulWidget {
#override
State createState() => new AdminAddVaccinationState();
}
class AdminAddVaccinationState extends State<AdminAddVaccination> {
#override
void initState() {
super.initState();
var stepInfo = Provider.of<StepInfo>(context); // ERROR!!
stepInfo.addToList = new VaccStep(); // ERROR!!
}
Widget build(BuildContext context) {
return new ChangeNotifierProvider(
builder: (context) => StepInfo(),
child: ScreenBody(),
);
}
}
class ScreenBody extends StatelessWidget {
#override
Widget build(BuildContext context) {
var stepInfo = Provider.of<StepInfo>(context);
return new Scaffold(
resizeToAvoidBottomPadding: false,
key: stepInfo.scaffoldKey,
body: new GestureDetector(
onTap: () {
FocusScope.of(context).requestFocus(new FocusNode());
},
child: new SafeArea(
top: true,
bottom: false,
child: new Stack(children: <Widget>[
new Opacity(
opacity: 0.04,
child: new Image.asset(
"assets/userProfile/heartBeat.png",
fit: BoxFit.cover,
height: 250.0,
),
),
new Column(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
new Container(
color: primaryGreen,
width: double.infinity,
height: 65.0,
child: new Stack(
children: <Widget>[
new Align(
alignment: Alignment.center,
child: stepInfo.loading
? JumpingText('......')
: new Container()),
new Align(
alignment: Alignment.centerLeft,
child: new Padding(
padding: EdgeInsets.only(top: 5.0, left: 20.0),
child: new InkWell(
child: new Container(
child: Icon(
Icons.arrow_back,
color: Colors.white,
size: 30.0,
),
),
onTap: () {
Navigator.pop(context);
},
),
),
),
],
),
),
new Padding(
padding: EdgeInsets.only(top: 0.0),
child: new Material(
elevation: 1.0,
color: Colors.transparent,
child: new Container(
color: borderColor,
width: double.infinity,
height: 5.0,
),
),
),
VaccName(),
],
),
ItemListing(),
AddStep(),
]),
)));
}
}
Error!! flutter: The following ProviderNotFoundError was thrown
building Builder: flutter: Error: Could not find the correct
Provider above this AdminAddVaccination Widget flutter:
flutter: To fix, please: flutter: flutter: * Ensure the
Provider is an ancestor to this AdminAddVaccination Widget
flutter: * Provide types to Provider flutter: * Provide
types to Consumer flutter: * Provide types to
Provider.of() flutter: * Always use package imports. Ex:
`import 'package:my_app/my_code.dart';

Answer 1

Simply add a constructor in your provider :
class StepInfo extends ChangeNotifier {
StepInfo() {
this.addToList = new VaccStep();
}
[...]
}

Answer 2

You must set listen:false and some delay to on initstate
Provider.of<StepInfo>(context, listen: false);
Future.delayed(Duration(milliseconds: 100)).then((_) {
stepInfo.addToList = new VaccStep();
});
same in this case or this

Answer 3

change the initState() & build() method in the AdminAddVaccination class as below:
var stepInfo;
#override
void initState() {
super.initState();
stepInfo = new StepInfo();
stepInfo.addToList = new VaccStep();
}
#override
Widget build(BuildContext context) {
return new ChangeNotifierProvider<StepInfo>(
builder: (context) => stepInfo,
child: ScreenBody(),
);
}