SharedPreferences called on null flutter

Question

I build a function that is used to store the token in shared preference and then fetch data from the server when I run my app for the very first time an error appears

The following NoSuchMethodError was thrown building AdminPage(dirty, state: AdminPageState#87bcd): flutter: The method '[]' was called on null. flutter: Receiver: null flutter: Tried calling:

and then the app works fine

P.S. my code is that

Future<Map<String, dynamic>> getCards(String userid) async {
  BuildContext context;
  String jWTtoken = '';
  try {
    final SharedPreferences prefs = await SharedPreferences.getInstance();

    //  prefs = await SharedPreferences.getInstance();
    jWTtoken = prefs.getString('token');
    tokenfoo();
  } catch (e) {
    Navigator.pushReplacement(
      context,
      MaterialPageRoute(builder: (BuildContext context) => AuthPage()),
    );
  }

  final Map<String, dynamic> authData = {
    'Userid': '261',
    // 'Email':_formData['Email'],
    // 'Password':_formData['Password'],
  };

  final http.Response response = await http.post(
      'hurl',
      body: json.encode(authData),
      headers: {
        'Content-Type': 'application/json',
        'Authorization': 'Bearer ' + jWTtoken
      });

  final Map<String, dynamic> responseData = json.decode(response.body);

  if (responseData["StatusCode"] == 200) {

    null;
  
  } else if (responseData["StatusCode"] == 401) {
    print(responseData);
    Logout();
  } else {
    print(responseData);
    Logout();

    null;
  }
  return responseData;
}

anything worng with it?

and in the debug mode the error appears in this line

 final SharedPreferences prefs = await SharedPreferences.getInstance();

the error :

══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════ flutter: The following NoSuchMethodError was thrown building AdminPage(dirty, state: AdminPageState#7db9a): flutter: The method '[]' was called on null. flutter: Receiver: null flutter: Tried calling: flutter: flutter: When the exception was thrown, this was the stack: flutter:

0 Object.noSuchMethod (dart:core/runtime/libobject_patch.dart:50:5) flutter: #1

AdminPageState.build (package:idb/pages/adminpage.dart:63:39) flutter:

2 StatefulElement.build (package:flutter/src/widgets/framework.dart:3809:27) flutter: #3

ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3721:15) flutter: #4
Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5) flutter: #5 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5) flutter: #6
StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3848:11) flutter: #7
ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5) flutter: #8
Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14) flutter: #9
Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12) flutter: #10
ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16) flutter: #11
Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5) flutter: #12 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2286:33) flutter: #13
_WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:676:20) flutter: #14
_WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:219:5) flutter: #15
_WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15) flutter: #16
_WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9) flutter: #17
_WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5) flutter: #18
_invoke (dart:ui/hooks.dart:154:13) flutter: #19 _drawFrame (dart:ui/hooks.dart:143:3)

Answer 1

Possibly because jwToken is empty at initialization. Try giving jwToken a string value such as "test".

Answer 2

This is happening because you don't initialize it before use

To avoid this you should initialize await SharedPref.init(); it on a _MyAppState class in initState() method like this

class _MyAppState extends State<MyApp> {

  void initState() async {
    super.initState();
    await SharedPref.init();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      locale: _locale,
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: appThemeColor,
        accentColor: Colors.lightBlueAccent,
      ),
      home: SplashScreen(),
      builder: (BuildContext context, Widget child) {
        return child;
      },
    );
  }
}

Create a global class to use globally

class SharedPref {
  static SharedPreferences pref;
  static Future init() async {
    pref = await SharedPreferences.getInstance();
  }
}

After you can use like this

SharedPref.pref.setBool("isLogin", true);