Flutter - type 'Future<dynamic>' is not a subtype of type 'List<Map<String, dynamic>>'

Question

I am using mysql1: ^0.19.2 and trying to fetch some data from a database to display in a select_form_field (select_form_field: "^2.2.0"). The database table I'm fetching data from contains 2 columns: 'id' and 'name' that should go as the value and label respectively in the List<Map<String, dynamic>> that fills the select_form_field.

I've created a method in my database.dart that fetches the data, fills a List<Map<String, dynamic>> and returns it. The signature of the connect()-method looks like this Future<MySqlConnection> connect() async {...}:

getData() async {
  List<Map<String, dynamic>> items = <Map<String, dynamic>>[];
  dynamic conn = await connect();

  var results = conn.query('select * from data');

  for (var row in results) {
    items.add({'value': row[0], 'label': row[1]});
  }

  return items;
}

In my main.dart I want to initialize this List and feed it to my select_form_field:

class MyCustomFormState extends State<MyCustomForm> {
  final List<Map<String, dynamic>> _items = getData(); // <-- Exception happens here

  Widget build(BuildContext context) {

    return Form(
      key: _formKey,
      child: Column( 
        children: <Widget>[
          Container(
            child: SelectFormField(
            controller: nameController,
            hintText: "...",
            items: _items, // <-- List goes here
          ...
}

I've tried adding helper methods without an async signature from which I could initialize the list, but that didn't work. Other solutions I've found on StackOverflow don't seem to suit my problem.

Answer 1

You have to wait for the data to get from an async function. For example,

final List<Map<String, dynamic>> _items = getData();

should be

final List<Map<String, dynamic>> _items = await getData();

So final code should be

late List<Map<String, dynamic>> _items;

@override
void initState() {
  super.initState();
  _getData();
}

_getData() async {
  _items = await getData();
}