Dropdown not showing data flutter

Question

I am trying to show a data in dropdown menu,but i have a weird problem i can't seem to figure it out.The problem is when open the view that contained dropdown menu the api data fetch data from server,it work as excepted but the data not shows to the dropdown for first time,in debug mode when i press hot realod the data is shown to dropdown menu not when the view shows first time

Dropdown menu

                  Flexible(
                    flex: 0,
                    child: Padding(
                      padding: const EdgeInsets.all(8.0),
                      child: Container(
                        height: 45,
                        width: 300,
                        decoration: BoxDecoration(
                            color: Colors.white,
                            borderRadius: BorderRadius.circular(5),
                            border: Border.all(
                                color: Color.fromRGBO(92, 52, 76, 1))),
                        child: DropdownButton<String>(
                            isExpanded: true,
                            itemHeight: 50,
                            underline: SizedBox(),
                            value: _selectedVehicle,
                            items: vehicle_list.map((vehicle) {
                              return DropdownMenuItem<String>(
                                value: vehicle.id,
                                child: new Text(
                                  vehicle.model,
                                  style: TextStyle(
                                      fontSize: 15,
                                      color: Color.fromRGBO(
                                          92, 52, 76, 1)),
                                ),
                              );
                            }).toList(),
                            hint: Padding(
                              padding: const EdgeInsets.all(8.0),
                              child: Text("Please Select Vehicle"),
                            ),
                            onChanged: (newValues) {
                              setState(() {
                                _selectedVehicle = newValues;
                              });
                            }),
                      ),
                    ),
                  )

API

Future<String> getVehicles() async {
    vehicle_list.clear();
    Future tokens = SharedPrefrence().getToken();
    tokens.then((data) async{
      token=data;
      var response = await http.get(Urls.BASE_URL + Urls.GET_VEHICLES, headers: {
        "Authorization": "Bearer " + token,
        "Content-Type": "application/json"
      });
      if (response.statusCode == 200) {
        print("vechiles " + response.body.toString());
        Map<String, dynamic> value = json.decode(response.body);
        try {
          var data = value['data'];
          for (int i = 0; i < data.length; i++) {
            var obj = data[i];
            vehicle_list.add(VehicleModel(
                obj['id'].toString(),
                obj['user_id'].toString(),
                obj['type'].toString(),
                obj['model'],
                obj['reg_no'],
                obj['fuel_type'].toString()));
          }
        } catch (e) {
          
          print(e.toString());
        }
      } else {
        print(response.body.toString());
      }
    });
  }

intilization

List<VehicleModel> vehicle_list = [];
String _selectedVehicle;

This how i call the function

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    getVehicles();
   
  }

Hamed Rezaee · Accepted Answer · 2020-08-22 18:34:19Z

I think this will resolve your issue:

Future<String> getVehicles() async {
    vehicle_list.clear();
    Future tokens = SharedPrefrence().getToken();
    tokens.then((data) async{
      token=data;
      var response = await http.get(Urls.BASE_URL + Urls.GET_VEHICLES, headers: {
        "Authorization": "Bearer " + token,
        "Content-Type": "application/json"
      });
      if (response.statusCode == 200) {
        print("vechiles " + response.body.toString());
        Map<String, dynamic> value = json.decode(response.body);
        try {
          var data = value['data'];
          for (int i = 0; i < data.length; i++) {
            var obj = data[i];
            vehicle_list.add(VehicleModel(
                obj['id'].toString(),
                obj['user_id'].toString(),
                obj['type'].toString(),
                obj['model'],
                obj['reg_no'],
                obj['fuel_type'].toString()));
          }
          
          // add this line...
          WidgetsBinding.instance.addPostFrameCallback((_) => setState((){}));
        } catch (e) {
          
          print(e.toString());
        }
      } else {
        print(response.body.toString());
      }
    });
  }

Shri Hari L · Accepted Answer · 2020-08-22 19:24:00Z

You have call setState at the end of the function to modify the state!
Something like this,

Future<String> getVehicles() async {
    vehicle_list.clear();
    Future tokens = SharedPrefrence().getToken();
    tokens.then((data) async{
      token=data;
      var response = await http.get(Urls.BASE_URL + Urls.GET_VEHICLES, headers: {
        "Authorization": "Bearer " + token,
        "Content-Type": "application/json"
      });
      if (response.statusCode == 200) {
        print("vechiles " + response.body.toString());
        Map<String, dynamic> value = json.decode(response.body);
        try {
          var data = value['data'];
          for (int i = 0; i < data.length; i++) {
            var obj = data[i];
            vehicle_list.add(VehicleModel(
                obj['id'].toString(),
                obj['user_id'].toString(),
                obj['type'].toString(),
                obj['model'],
                obj['reg_no'],
                obj['fuel_type'].toString()));
          }
          setState(() {});
        } catch (e) {
          
          print(e.toString());
        }
      } else {
        print(response.body.toString());
      }
    });
  }

Hope that works!

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