Flutter: How to read preferences at Widget startup? - dart

Question

I have been trying to read preferences at Widget startup but have been unable to find a solution.
I wish to show the users name in a TextField (which they can change) and store it in preferences so that it is shown as soon as they go back to the page.
class _MyHomePageState extends State<MyHomePage> {
TextEditingController _controller;
:
:
Future<Null> storeName(String name) async {
SharedPreferences prefs = await SharedPreferences.getInstance();
prefs.setString("name", name);
}
#override
initState() async {
super.initState();
SharedPreferences prefs = await SharedPreferences.getInstance();
_controller = new TextEditingController(text: prefs.getString("name"));
}
#override
Widget build(BuildContext context) {
:
:
return new TextField(
decoration: new InputDecoration(
hintText: "Name (optional)",
),
onChanged: (String str) {
setState(() {
_name = str;
storeName(str);
});
},
controller: _controller,
)
}
}
I got the idea for using async on initState() from :
flutter timing problems on stateful widget after API call
But the async seems to cause this error on startup :
'package:flutter/src/widgets/framework.dart': Failed assertion: line 967 pos 12:
'_debugLifecycleState == _StateLifecycle.created': is not true.
I looked for examples of FutureBuilder but cannot seem to find any which are similar to what I am trying to do.

Answer 1

I would suggest not to use the async on initState(). but you can do this in a different way by wrapping up your SharedPreferences inside another function and declaring this as async.
I have modified your code . Please check if this works. Many Thanks.
modified code:
class _MyHomePageState extends State<MyHomePage> {
TextEditingController _controller;
String _name;
Future<Null> getSharedPrefs() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
_name = prefs.getString("name");
setState(() {
_controller = new TextEditingController(text: _name);
});
}
#override
void initState() {
super.initState();
_name = "";
getSharedPrefs();
}
#override
Widget build(BuildContext context) {
return new TextField(
decoration: new InputDecoration(
hintText: "Name (optional)",
),
onChanged: (String str) {
setState(() {
_name = str;
storeName(str);
});
},
controller: _controller,
);
}
}
Let me know if this helps.
Thank you.

Answer 2

initState() is a synchronous function where you cannot mark async, as async convert that function into asynchronous.
Below code helps to load shared preference values at loading time, and used to update widgets.
#override
void initState() {
super.initState();
SharedPreferences.getInstance().then((prefValue) => {
setState(() {
_name = prefValue.getString('name')?? "";
_controller = new TextEditingController(text: _name);
})
});
}

Answer 3

Doing it at the app-level.
SharedPreferences prefs;
void main() async {
WidgetsFlutterBinding.ensureInitialized();
prefs = await SharedPreferences.getInstance();
// Rest of your code...
}

Answer 4

You can also User Timer or Future.delayed
First Create Your Method for SharedPreference
Future getId() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
id = prefs.getString("id");
}
then in your initMethod
#override
void initState() {
getId();
Timer(Duration(microseconds: 250), () {
_controller = new TextEditingController(text: id);
});
super.initState();
}