Question 76002 in Flutter Question posted in
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Flutter Shared Preferences cannot use async/await, so I must use a then

void _authKey() {
    Hmac hmacSha = new Hmac(sha256, utf8.encode("604ec80ffa552786f409590994dc89cfef040b72"));
    String hashValue = "";
    List<String> sortedKeys = _datas.keys.toList()..sort();
    sortedKeys.forEach((f) => hashValue += _datas[f]! + "+");
    print("waw");
    
    SharedPreferences.getInstance().then((prefs) => () {
      print("wow");
      String? token = prefs.getString('apitoken');

      print("the auth key is " + token.toString());

      key = hmacSha
        .convert(utf8.encode(hashValue + token.toString()))
        .toString();

    });
    
}

Why isn’t "wow" printed ? It’s never displayed in the console… But "waw" is…
So why is the SharedPreferences.getInstance().then((prefs) => () neved trigged ?

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3

Answers


  1. 0

    Because you are creating anonymous function

    (prefs) => () {

    What it should be

    .then((prefs) {
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  2. 0

    you can write like this too

    final Future<SharedPreferences> sharedPreferences = SharedPreferences.getInstance();
sharedPreferences.then((value) async => {

      Future.delayed(Duration.zero,  () {

        // code more...

      })

});

    or write like this

    sharedPreferences.then((value) async {
    
          // code more...
    
    });
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  3. 0

    Use SharedPrefs Class

    class SharedPrefs {
 static SharedPreferences _sharedPrefs;

factory SharedPrefs() => SharedPrefs._internal();

 SharedPrefs._internal();

Future<void> init() async {
_sharedPrefs ??= await SharedPreferences.getInstance();
 }
  String get username => _sharedPrefs.getString('apitoken') ?? "";
 set apitoken(String value) {
  _sharedPrefs.setString('apitoken', value);
   }
   }

    **Call init function before runApp **

    await SharedPrefs().init();
 
runApp(
MyApp(),
);

 ......
 //you can use SharedPrefs as follow
   String? token = SharedPrefs().apitoken;

  print("the auth key is " + token.toString());

    .............
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