Flutter DropDownButton using FutureBuilder value is not updating after selecting values from DropdownItems

Question

I have been trying to code this app using Flutter and I want to make a Dropdown that displays the values received from a JSON response via provider. The response is successful from the service and correctly fetches the data. Dropdown is wrapped in a FutureBuilder, the information can be displayed without problems in the Dropdown, the problem is generated when I want to select an element, it is not updated, for this reason it is not reflected.

My code:

 List<Datum> listDatumEnterprise;
Datum _selectEnterprise;

return FutureBuilder(
    future: getInformationAdministrative.enterpriseDataGet(),
    builder: (BuildContext context, AsyncSnapshot<List<Datum>> snapshot) {
      if (snapshot.hasData) {
        listDatumEnterprise = snapshot.data;
        return CustomDropDown<Datum>(
          title: 'Selecciona empresa',
          value: _selectEnterprise,
          onChanged: (Datum datum) {
            setState(() {
              _selectEnterprise = datum;
              print(_selectEnterprise.id);
            });
          },
          dropdownMenuItemList: listDatumEnterprise?.map((Datum item) {
                return new DropdownMenuItem<Datum>(
                  child: Text(item.alias),
                  value: item,
                );
              })?.toList() ??
              [],
        );
      } else {
        return CircularProgressIndicator();
      }

Answer 1

The problem is that you are initializing _selectEnterprise inside your build , calling setState() will call build and will re-initiate the value again to empty, move Datum _selectEnterprise outside your build. Also be sure to have distinct values for the DropdownMenuItem.

Answer 2

I have wrapped my DropdownButton with StatefulBuilder. This is the only way I could change the data of DropdownButton without recalling FutureBuilder.

Demo code:

StatefulBuilder(builder: (context, setState) {
                return DropdownButton<String>(
                  borderRadius: BorderRadius.circular(
                    10,
                  ),
                  hint: Text(
                    "Your Hint",
                  ),
                  value: selectedValue, //your selected value
                  isExpanded: true,
                  items: your_list.map((String value) { //your list here
                    return DropdownMenuItem<String>(
                      value: value,
                      child: Text(value),
                    );
                  }).toList(),
                  onChanged: (value) {
                    setState(() => selectedValue = value); //your selected value
                  },
                );
              }),

Learn more from: StatefulBuilder