Flutter DropdownButton get value from SharedPreferences - flutter

Question

So I making an app in which I have DropdownButton. I want to get the value parameter from SharedPreferences. But SharedPreferences.getInstance returns Future, not String. How could I return a String instead of Future?
This is a function for reading from SharedPreferences
_read() async {
final prefs = await SharedPreferences.getInstance();
final key = 'cur_r';
final value = prefs.getString(key) ?? "";
print('read: $value');
return value;
}
Here is the dropdown Button code:
body: Center(
child: DropdownButton<String>(
value: __read(),
onChanged: (String newValue) {
setState(() {
dropdownValue = newValue;
_save(newValue);
_read();
});
},
items: ['one', 'two', 'three']
.map<DropdownMenuItem<String>>((String value) {
return DropdownMenuItem<String>(
value: value,
child: Text(value),
);
}).toList(),
),
),

Answer 1

This is a better approach of doing it.
class HomePage extends StatefulWidget {
#override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
// make all of them instance variable
String dropdownValue;
SharedPreferences prefs;
final _key = 'cur_r';
#override
void initState() {
super.initState();
_read(); // read in initState
}
_read() async {
prefs = await SharedPreferences.getInstance();
setState(() {
dropdownValue = prefs.getString(_key) ?? "one"; // get the value
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text("")),
body: Center(
child: DropdownButton<String>(
value: dropdownValue,
onChanged: (String newValue) {
setState(() {
dropdownValue = newValue;
});
prefs.setString(_key, dropdownValue); // save value to SharedPreference
},
items: ['one', 'two', 'three'].map<DropdownMenuItem<String>>((String value) {
return DropdownMenuItem<String>(
value: value,
child: Text(value),
);
}).toList(),
),
),
);
}
}