I am getting error like this Unhandled Exception: Looking up a deactivated widget's ancestor is unsafe - flutter

Question

What I trying to do here is getting data from the 000webhost.com and passing that to my model class. That model class is being passed to the provider. Now when I try to display the information in my screen i am getting error.
In this case i have a model class called StudentData.
class StudentData {
final String rollNumber;
final String firstName;
final String lastName;
StudentData({
this.rollNumber,
this.firstName,
this.lastName,
});
}
Here I am fetching data using http package from internet.
And passing the decoded data to the StudentData class and passing that to my data_provider
import 'package:http/http.dart' as http;
void getStudentData(String currentEmail, BuildContext context) async {
final _url = 'https://aaa.000webhostapp.com/getStudentData.php';
final response = await http.post(_url, body: {'email': currentEmail});
var data = response.body;
final decodedData = jsonDecode(data);
final myRollNumber = decodedData['roll_number'];
final myFirstName = decodedData['first_name'];
final myLastName = decodedData['last_name'];
final myStudentData = StudentData(
rollNumber: myRollNumber, firstName: myFirstName, lastName: myLastName);
Provider.of<DataProvider>(context, listen: false)
.getMyStudentData(myStudentData);
}
Here is my DataProvider
class DataProvider extends ChangeNotifier {
StudentData myStudentData;
void getMyStudentData(StudentData studentData) {
myStudentData = studentData;
notifyListeners();
}
}
After that I have tried to fetch those information in my Screen
class StudentDashboard extends StatelessWidget {
#override
Widget build(BuildContext context) {
return SafeArea(
child: Scaffold(
body: Center(
child:
Text(Provider.of<DataProvider>(context).myStudentData.rollNumber),
),
),
);
}
}
Then the error be like
======== Exception caught by widgets library =======================================================
The following NoSuchMethodError was thrown building StudentDashboard(dirty, dependencies: [_InheritedProviderScope<DataProvider>]):
The getter 'rollNumber' was called on null.
Receiver: null
Tried calling: rollNumber
The relevant error-causing widget was:
StudentDashboard file:///D:/Other/App/Flutter/my_ecampus/lib/views/screens/auth_screens/login_screen.dart:62:53
When the exception was thrown, this was the stack:
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:51:5)
#1 StudentDashboard.build (package:my_ecampus/views/screens/main_screens/student_screens/student_dashboard.dart:38:69)
#2 StatelessElement.build (package:flutter/src/widgets/framework.dart:4701:28)
#3 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4627:15)
#4 Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
...
====================================================================================================
E/flutter ( 7682): [ERROR:flutter/lib/ui/ui_dart_state.cc(177)] Unhandled Exception: Looking up a deactivated widget's ancestor is unsafe.
E/flutter ( 7682): At this point the state of the widget's element tree is no longer stable.
E/flutter ( 7682): To safely refer to a widget's ancestor in its dispose() method, save a reference to the ancestor by calling dependOnInheritedWidgetOfExactType() in the widget's didChangeDependencies() method.
E/flutter ( 7682): #0 Element._debugCheckStateIsActiveForAncestorLookup.<anonymous closure> (package:flutter/src/widgets/framework.dart:3906:9)
E/flutter ( 7682): #1 Element._debugCheckStateIsActiveForAncestorLookup (package:flutter/src/widgets/framework.dart:3920:6)
E/flutter ( 7682): #2 Element.getElementForInheritedWidgetOfExactType (package:flutter/src/widgets/framework.dart:3986:12)
E/flutter ( 7682): #3 Provider._inheritedElementOf (package:provider/src/provider.dart:324:34)
E/flutter ( 7682): #4 Provider.of (package:provider/src/provider.dart:281:30)
E/flutter ( 7682): #5 getStudentData (package:my_ecampus/business_view/services/database/getData_database.dart:19:12)
E/flutter ( 7682): <asynchronous suspension>
E/flutter ( 7682): #6 LoginScreen._login (package:my_ecampus/views/screens/auth_screens/login_screen.dart:60:9)
E/flutter ( 7682): <asynchronous suspension>
E/flutter ( 7682): #7 LoginScreen.build.<anonymous closure>.<anonymous closure> (package:my_ecampus/views/screens/auth_screens/login_screen.dart:198:31)
E/flutter ( 7682): #8 _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:993:19)
E/flutter ( 7682): #9 _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:1111:38)
E/flutter ( 7682): #10 GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:183:24)
E/flutter ( 7682): #11 TapGestureRecognizer.handleTapUp (package:flutter/src/gestures/tap.dart:598:11)
E/flutter ( 7682): #12 BaseTapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:287:5)
E/flutter ( 7682): #13 BaseTapGestureRecognizer.acceptGesture (package:flutter/src/gestures/tap.dart:259:7)
E/flutter ( 7682): #14 GestureArenaManager.sweep (package:flutter/src/gestures/arena.dart:157:27)
E/flutter ( 7682): #15 GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:362:20)
E/flutter ( 7682): #16 GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:338:22)
E/flutter ( 7682): #17 RendererBinding.dispatchEvent (package:flutter/src/rendering/binding.dart:267:11)
E/flutter ( 7682): #18 GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:295:7)
E/flutter ( 7682): #19 GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:240:7)
E/flutter ( 7682): #20 GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:213:7)
E/flutter ( 7682): #21 _rootRunUnary (dart:async/zone.dart:1206:13)
E/flutter ( 7682): #22 _CustomZone.runUnary (dart:async/zone.dart:1100:19)
E/flutter ( 7682): #23 _CustomZone.runUnaryGuarded (dart:async/zone.dart:1005:7)
E/flutter ( 7682): #24 _invoke1 (dart:ui/hooks.dart:265:10)
E/flutter ( 7682): #25 _dispatchPointerDataPacket (dart:ui/hooks.dart:174:5)
E/flutter ( 7682):
This is my main class and i am using multiprovider here.
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MultiProvider(
providers: [
ChangeNotifierProvider<WidgetProvider>(
create: (context) => WidgetProvider()),
ChangeNotifierProvider<DataProvider>(
create: (context) => DataProvider()),
],
child: MaterialApp(
home: LoginScreen(),
),
);
}
}
This is where I call getStudentData function
void _login({String email, String password, BuildContext context}) async {
final loginResponse =
await loginDatabase(email: email, password: password, context: context);
if (loginResponse.isNotEmpty) {
final isStaff = email.contains(RegExp(r'.ce#srit.org$'));
if (isStaff == true) {
getStaffData(email, context);
Navigator.pushReplacement(
context, MaterialPageRoute(builder: (context) => StaffDashboard()));
} else {
getStudentData(email, context);//here is the getStudentData() function
Navigator.pushReplacement(context,
MaterialPageRoute(builder: (context) => StudentDashboard()));
}
} else {
print('Login Failed from loginDatabase(){}');
}
}

Answer 1

The HTTP request is sent to the provider listen: false because it can not listen. So that you can call the method. That's why I designed it from scratch for you. I hope you understand. It will probably work if you do it as I did.
import 'package:http/http.dart' as http;
Future<StudentData> _getStudentData(String currentEmail, BuildContext context)async {
final _url = 'https://aaa.000webhostapp.com/getStudentData.php';
final response = await http.post(_url, body: {'email': currentEmail});
var data = response.body;
if (data.isEmpty) return null;
final decodedData = jsonDecode(data);
final myRollNumber = decodedData['roll_number'];
final myFirstName = decodedData['first_name'];
final myLastName = decodedData['last_name'];
final myStudentData = StudentData(
rollNumber: myRollNumber, firstName: myFirstName, lastName: myLastName);
return MystudentData;
}
class DataProvider extends ChangeNotifier {
StudentData myStudentData;
void getMyStudentData(StudentData studentData) {
myStudentData = studentData;
notifyListeners();
}
}
Future getMyStudentDataAsync() async {
StudentData result = await _getStudentData();
getMyStudentData(result);
}
class StudentDashboard extends StatelessWidget {
#override
void initState() {
super.initState(); getRequest();
}
future getRequest()async{
Provider.of<DataProvider>(context, listen: false)
.getMyStudentDataAsync();
}
#override
Widget build(BuildContext context) {
DataProvider _dataProvider = Provider.of<DataProvider>(context);
return SafeArea(
child: Scaffold(
body: Center(
child:
Text( _dataProvider.myStudentData.rollNumber),
),
),
);
}
}