Flutter correctly print map having a future map - flutter

Question

someone can help with this code?
I must print a query result inside the dropdown as List
The error flutter give me back is:
The following NoSuchMethodError was thrown building
DropDownFormField(dirty, dependencies: [_FormScope], state:
FormFieldState#e264a): Class 'Future<List>' has no
instance method '[]'. Receiver: Instance of 'Future<List>'
Tried calling: The relevant error-causing widget was:
DropDownFormField
I've tryed getAllBrockers and getAllBrockers2 way
class _AutomationAddScreen extends State<AutomationAdd> {
DataRepository _repository;
final _formKey = GlobalKey<FormState>();
String _broN = "";
Future<Map> _broMap;
Future<List> _bro;
static Future<List> getAllBrockers2(Future<List<Brockers>> l) async {
List q;
List<Brockers> b = await l;
for (var i = 0; i < b.length; i++) {
q.add(DataList(b[i].name, b[i].id));
}
return q;
}
static Future<Map> getAllBrockers(Future<List<Brockers>> l) async {
Map hBro;
Map m;
List<Brockers> b = await l;
for (var i = 0; i < b.length; i++) {
m = {"display": b[i].name, "value": b[i].id};
hBro.addAll(m);
}
return hBro;
}
#override
void initState() {
super.initState();
_repository = SqlRepository();
//_broMap = getAllBrockers(_repository.getAllBrockers());
_bro = getAllBrockers2(_repository.getAllBrockers());
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: Form(
key: _formKey,
child: ListView(
children: <Widget>[
//SELECT BROCKER
Padding(
padding: EdgeInsets.only(top: 16),
child: DropDownFormField(
titleText: 'Connessione',
hintText: 'Selezionane uno',
value: _broN,
//dataSource: [_broMap],
dataSource: [_bro],
textField: 'display',
valueField: 'value',
onChanged: (display) {
setState(() {
_broN = display.toString();
});
},
),
),
],
),
),
));
}
}
class DataList {
String display;
int value;
DataList(this.display, this.value);
#override
String toString() {
return '{ ${this.display}, ${this.value} }';
}
}

Answer 1

Instead of using Future<List> or Future<Map>, you should use List or Map. The error specifically mentions that it cannot call [] on Future<List>.
The DropdownFormField is unable to create its list of items because you have provided a Future.
You can try using the following approach -
class _AutomationAddScreen extends State<AutomationAdd> {
DataRepository _repository;
final _formKey = GlobalKey<FormState>();
String _broN = "";
Map _broMap; // New
List _bro = List<DataList>(); // New
static Future<void> getAllBrockers2() async { // New
final b = await _repository.getAllBrockers(); // New
for (var i = 0; i < b.length; i++) {
_bro.add(DataList(b[i].name, b[i].id)); // New
}
setState(() {}); // New
}
static Future<Map> getAllBrockers(Future<List<Brockers>> l) async {
Map hBro = {}; // New
Map m;
List<Brockers> b = await l;
for (var i = 0; i < b.length; i++) {
m = {"display": b[i].name, "value": b[i].id};
hBro.addAll(m);
}
return hBro;
}
#override
void initState() {
super.initState();
_repository = SqlRepository();
//_broMap = getAllBrockers(_repository.getAllBrockers());
getAllBrockers2(); // New
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: Form(
key: _formKey,
child: ListView(
children: <Widget>[
//SELECT BROCKER
Padding(
padding: EdgeInsets.only(top: 16),
child: DropDownFormField(
titleText: 'Connessione',
hintText: 'Selezionane uno',
value: _broN,
//dataSource: [_broMap],
dataSource: [_bro],
textField: 'display',
valueField: 'value',
onChanged: (display) {
setState(() {
_broN = display.toString();
});
},
),
),
],
),
),
));
}
}
class DataList {
String display;
int value;
DataList(this.display, this.value);
#override
String toString() {
return '{ ${this.display}, ${this.value} }';
}
}