How to reload elements after getting data from shared preferences?

Question

I am able to fetch data from shared preferences. I want to reload the data on the page after reopening the app fetching data from shared preferences. Right now, im trying to load data from shared preferences to a list which is called in the initState().

Note:- when i navigate to other page and come page to page on which data needs to be updated. The data is updated successfully. But i want to do this everytime app is opened again

class WeatherApp extends StatefulWidget {
  const WeatherApp({Key? key}) : super(key: key);
  static const String idScreen = "weather";

  @override
  _WeatherAppState createState() => _WeatherAppState();
}



class _WeatherAppState extends State<WeatherApp> {

  final preferenceService = PreferencesService();

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance!.addObserver(this);

  }

  @override
  void dispose() {
    WidgetsBinding.instance!.removeObserver(this);
    super.dispose();
  }
  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    print('state = $state');

    if (state == AppLifecycleState.resumed){
      setState(() {
        preferenceService.getData();
      });

    }

}




class PreferencesService{

void saveData(List<dynamic> data) async{
  final preferences = await SharedPreferences.getInstance();
 
  String encodedData = jsonEncode(data);

  await preferences.setString("weather_data", encodedData);

}

void getData() async{
  final preferences = await SharedPreferences.getInstance();

  var jsonData = preferences.getString("weather_data");


  if (jsonData == null){
    locationList = [];
  }
  else{
    locationList.clear();
    var dataList = json.decode(jsonData);
    for (var e in dataList) {
      locationList.add(
          WeatherModel(
            weatherId: e["weatherId"],
            cityId: e["cityId"],
            city: e["city"],
            dateTime: e["dateTime"],
            temperature: e["temperature"],
            weatherType: e["weatherType"],
            iconUrl: e["iconUrl"],
            wind: e["wind"],
            rain: e["rain"],
            humidity: e["humidity"],
          )
      );
      print("fetching Data");
      print(locationList);

  }
  }

}

}
  

Im trying to update text for which i have made another stateful widget(Text is not updating even after saving data to a global list and fetching data on resumed)

Column(
    crossAxisAlignment: CrossAxisAlignment.start,
    children: [
      Text(locationList.length != 0 ? locationList[widget.index].temperature : "--\u2103"),
      Row(
          children: [ 
SvgPicture.asset(locationList.length != 0 ? locationList[widget.index].iconUrl : "assets/rain.svg", width: 30,height: 30,color: Colors.white,),
             Text(locationList.length != 0 ? locationList[widget.index].weatherType : "Rainy",style: GoogleFonts.openSans(fontSize: 20,fontWeight: FontWeight.bold,color: Colors.white)),
                        ],
                      ),

                    ],
                  ),
                ],
              ),

Answer 1

To implement logic depending on application state you have to setup observer to application life cycle events and add the following override to your state class, in your case AppLifecycleState.resumed is the one that you need to monitor:

class _MyWidgetState extends State<MyWidget> with WidgetsBindingObserver {
  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance!.addObserver(this);
  }

  @override
  void dispose() {
    WidgetsBinding.instance!.removeObserver(this);
    super.dispose();
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    // possible values of state:
    // AppLifecycleState.inactive
    // AppLifecycleState.detached
    // AppLifecycleState.paused
    // AppLifecycleState.resumed
  }
}

Include this line in your main() function, this will ensure that you can safely use WidgetsBinding.instance!:

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(App());
}

Furthermore, there is no point calling setState from initState. initState is only called once, check here.