Try correcting the name to the name of an existing method, or defining a method named 'fetchCity'

Question

In order to get weather information about an entered city, I Created a fetch city function as bellow :

class CityModel  {

  final String? name;
  final String? lat;
  final String? lon;
  var cityJSON;

  CityModel({
    this.name, 
    this.lat, 
    this.lon});
    String get city{
      return city;
    }
  
  Future<CityModel?>  fetchCity(String cityName) async{
  if (cityJSON == null) {
      var link ="https://raw.githubusercontent.com/dr5hn/countries-states-cities-database/master/cities.json";
      var  response =  await http.get(Uri.parse(link));
      if (response.statusCode == 200) {
          cityJSON = json.decode(response.body);
      }
  }
   for (var i = 0; i < cityJSON.length; i++) {
      if (cityJSON[i]["name"].toString().toLowerCase() == cityName.toLowerCase()) {
         return CityModel(
           name: cityJSON[i]["name"].toString(),
           lat: cityJSON[i]["latitude"].toString(),
           lon: cityJSON[i]["longitude"].toString(),
         );
      }
   }

return null;
  }
  
}

then, I tried to call it in another file as shown bellow :

 class CurrentWeather extends StatefulWidget {
     
   final Function() updateData;
   CurrentWeather(this.updateData);
   
  @override
  State<CurrentWeather> createState() => _CurrentWeatherState();
}

class _CurrentWeatherState extends State<CurrentWeather> {
  bool searchBar = false;
  bool updating = false;
  var focusNode = FocusNode();  
   
    
    @override
    Widget build(BuildContext context) {
      return  GestureDetector(
        onTap: (){
          if(searchBar)
          setState(() {
            searchBar = false;
          });
        },
        child: GlowContainer(
                height: MediaQuery.of(context).size.height - 250,
              padding: EdgeInsets.only(top: 20, left: 30, right: 30, bottom: 20),
                margin: EdgeInsets.all(2),
                glowColor: Color(0xff00A1FF).withOpacity(0.8),
                borderRadius: BorderRadius.only(
                 bottomLeft: Radius.circular(60),
                  bottomRight: Radius.circular(60), 
                ),
                color: Color(0xff00A1FF), 
                spreadRadius: 5,
                child: Column(
                  children: [ 
                    Container(

                      ///////////// If the user click the Search bar 
                      child:  searchBar?  
                      TextField(
                        focusNode: focusNode,
                        decoration: InputDecoration(
                          border: OutlineInputBorder(borderRadius: BorderRadius.circular(10),),
                          fillColor: Color(0xff030317),
                          filled: true,
                          hintText: "Enter a city Name",
                        ),
                        textInputAction: TextInputAction.search,
                        onSubmitted: (value) async{
            //My call is here //////////
                     CityModel temp  = await fetchCity(value);
                          if (temp == null) {
                              showDialog(
                                context: context, 
                                builder: (BuildContext context){
                                  return AlertDialog(
                                    backgroundColor: Color(0xff030317),
                                    title: Text("City not found "),
                                    content: Text("Please check the city name"),
                                    actions: [
                                      TextButton(
                                        onPressed: (){
                                          Navigator.of(context).pop();
                                        },
                                         child: Text("ok")),
                                    ],
                                  );
                                }
                                );
                                searchBar = false;
                                return;
                          }

                           city = temp.city;
                           lat = temp.lat!;
                           lon = temp.lon!;
                           updating = true;
                            setState(() {
                              
                            });
                            widget.updateData;
                            searchBar = false;
                            updating = false;
                            setState(() {
                              
                            });
                        },
                      )
                      : Row(
                        mainAxisAlignment: MainAxisAlignment.spaceBetween,
                        children: [
                          Icon(CupertinoIcons.square_grid_2x2,
                          color: Colors.white,
                          ),
                          Row(
                            children: [
                            Icon(CupertinoIcons.map_fill, color: Colors.white,),
                            GestureDetector(
                              onTap: (){
                                searchBar = true;
                                setState(() {
                                  
                                });
                                focusNode.requestFocus();
                              },
                              child: Text("" + city, style: TextStyle(
                                fontWeight: FontWeight.bold,
                                fontSize: 30,
                              ),
                              ),
                            ),
                            ],
                          ),
                           Icon(Icons.more_vert, color: Colors.white,),
                        ],
                      ),
                    ),
                    Container(
                      margin: EdgeInsets.only(top: 10),
                      padding: EdgeInsets.all(10),
                      decoration: BoxDecoration(
                        border: Border.all(width: 0.2, color: Colors.white),
                        borderRadius: BorderRadius.circular(30),
                      ),
                      child: Text(
                        updating ? 'updating' : 'updated', style: TextStyle(
                        fontWeight: FontWeight.bold,
                      ),
                      ),
                    ),
                    
                    Container(
                       height: 300, 
                      
                           child: Stack(
                            children: [
                              Image(
                                width:200 ,
                                height:200 ,
                                image: AssetImage(currentTemp!.image!),
                                fit: BoxFit.fill,
                                ),
                                SizedBox(height: 10,),
                                Positioned(
                                  bottom: 0,
                                  right: 0,
                                  left: 0,
                                  child:Center(
                                    child: Column(
                                      children: [
                                         GlowText(currentTemp!.current!.toString(), 
                                         style: TextStyle(
                                           
                                           fontSize: 100,
                                           fontWeight: FontWeight.bold,
                                         ),
                                         ), 
                                         Text(currentTemp!.name!, 
                                         style: TextStyle(fontSize: 20,),
                                         ),
                                          Text(currentTemp!.day!, 
                                         style: TextStyle(fontSize: 18,),
                                         ),
                                      ],
                                    ),
                                  ),
                                   ),
                            ],
                             ),
                        ),
                       Divider(color: Colors.white,),
                       SizedBox(height: 5,),
                       ExtraWeather(currentTemp!),
                  ],
                ),
            
         
        ),
      );
    }
}

I'm getting this error:

The method 'fetchCity' isn't defined for the type '_CurrentWeatherState'. Try correcting the name to the name of an existing method, or defining a method named 'fetchCity'. in Advance thank you for your help

Answer 1

Since you declared your method inside CityModel you have to create an instance of it to call fetchCity.

final CityModel cityModel = CityModel();
final CityModel? city = awaitfetchCity('MyCity');

If you don't want to create an instance of CityModel you can either make fetchCity a global method or a static.

static Future<CityModel?>  fetchCity(String cityName) async{ ... }

// Call the method
final CityModel? city = await CityModel.fetchCity('MyCity');