Flutter- Why I can't see the data inside the Dropdown - flutter

Question

I'm new to Flutter and I can't understand why I can't see the data inside the DropDownButton even tho the lists that I use to create the DropDownButton have the data inside them. Can anyone explain to me why is this happening? The only clue I have is that the DropDownButton starts the creation before I create the list from which is taking the data.
The problem is that my dropdown list is empty.
I provide the entire code below.
Code :
import 'package:flutter/material.dart';
import 'ListOfClienti.dart';
class CreateClient extends StatefulWidget {
#override
_CreateClientState createState() => _CreateClientState();
}
class _CreateClientState extends State<CreateClient> {
String ClientCod = '';
String currentClient = '';
List<String> listNameOfClients = [];
List<DropdownMenuItem<String>> actualList2 = [];
void getClientsName() {
for (var i = 0; i <= ListDatabase.length - 1; i++) {
var name = ListDatabase[i].nome;
print(name);
listNameOfClients.add(name);
}
}
void createListWithClientName() {
for (String oneByOneClient in listNameOfClients) {
var VariableToInsert2 = DropdownMenuItem(
child: Text(oneByOneClient),
value: oneByOneClient,
);
actualList2.add(VariableToInsert2);
}
}
//Method that allows me to create the DropDownButton
DropdownButton<String> createNameMachine() {
return DropdownButton(
items: actualList2,
style: TextStyle(
color: Colors.black,
fontFamily: 'Keqima',
fontSize: 15,
),
value: currentClient,
onChanged: (clientSelected) {
setState(() {
currentClient = clientSelected;
});
},
);
}
#override
Widget build(BuildContext context) {
return Container(
color: Color(0xff757575),
child: Container(
decoration: BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.only(
topLeft: Radius.circular(20),
topRight: Radius.circular(20),
),
),
child: Column(
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Padding(
padding: EdgeInsets.all(16),
child: TextField(
decoration: InputDecoration(
border: OutlineInputBorder(),
labelText: 'Inserisci il codice cliente',
),
onChanged: (textInsideTheField) {
ClientCod = textInsideTheField;
},
),
),
Padding(
padding: EdgeInsets.all(16),
child: Row(
children: <Widget>[
FlatButton(
onPressed: () {
getClientsName();
createListWithClientName();
print(actualList2.length);
},
child: Text(
'Clienti : ',
style: TextStyle(
fontSize: 20,
fontFamily: 'Keqima',
),
),
),
SizedBox(
width: 20,
),
createNameMachine(),
],
),
),
],
),
),
);
}
}

Answer 1

To fix this problem I had to change to things :
Thing: I had to change the List from this List listNameOfClients = []; to this List listNameOfClients = [''];
I had to integrate the setState and inside to call the functions.
setState(() {
getClientsName();
createListWithClientName();
});