I’m a little new to flutter. I have two DropdownButtons. The second depends on the selection of the first.
The data of the first I retrieve from the database. It poses no problem. Mais le second n’affiche aucune donnée bien que la liste de ses données ne soit pas vide.
First DropdownButton

Province?  maProvince;
Ville? ville;
List<Ville> villes = [];
FutureBuilder<List<Province>>(
    future: dbHelper.allProvinces(),
    builder: (context,snapshot){
    if(snapshot.connectionState == ConnectionState.waiting){
         return CircularProgressIndicator();
    }else if(snapshot.hasError){
         return Text("Erreur du chargement des provinces.");
    }else if (!snapshot.hasData || snapshot.data!.isEmpty){
         return Text("Aucune province trouvée.");
    }else{
         List<Province> provinces = snapshot.data!;
         return DropdownButtonFormField<Province>(
                  value: maProvince,
                  decoration: InputDecoration(
                     labelText: "Choisir une province",
                     border: OutlineInputBorder(),
                  ),
                  items: provinces.map((province){
                    return DropdownMenuItem<Province>(
                       value: province,
                       child: Text((province.nomProvince))
                    );
                  }).toList(),
                  onChanged: (province) async{
                      final choises = await dbHelper.citiesOfAProvince(province!.id);
                      setState(() {
                         maProvince = province!;
                         villes = choises;
                         ville = choises[0];
                      });
                  },
                             
                );
           }
        }
    )

The variable villes,I use to load data of my second dropdownButton contains the data when I select an element from the first, but But no items are displayed.
Second DropdownButton

DropdownButtonHideUnderline(
   child: ButtonTheme(
      child: DropdownButtonFormField<Ville>(
               value: ville,
               onChanged: (Ville? newValue) async{
                    setState((){
                    ville = newValue!;});
               },
               
               items: villes.map((ville){
                   return DropdownMenuItem<Ville>(
                        child: Text(ville.nom_ville),
                        value: ville
                    );
              }).toList(),
         )
     )
 )

What am I not doing well?
Help please !