Question 290012 in Flutter Question posted in
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Flutter/Dart Future

class _WorterBuchState extends State<WorterBuch> with TickerProviderStateMixin {
  var wordPair= '' ;
  
@override
void initState(){

  super.initState();
  load();
}

Future<void>     load() async{
  SharedPreferences prefs = await SharedPreferences.getInstance();
  prefs.setString('key', 'value');
  wordPair =  await "key : " +  (prefs.getString('key') as String);

}
  @override
  Widget build(BuildContext context)  {
print(wordPair);

I have this class and this async function. I run the async function in the initState call but when build method runs it prints nothing. How can i solve this problem or how can i wait how the Future to finish? Can anybody please helpp

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2

Answers


  1. 0

    Future method takes some frame to fetch data, try using FutureBuilder like

      Future<String> load() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.setString('key', 'value');
    final wordPair = "key: ${prefs.getString('key')}";
    return wordPair;
  }
  late final future = load();

  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      future: future,
      builder: (context, snapshot) {
        if (snapshot.hasData) {
          final wordPair = snapshot.data ;
          return Text(wordPair??'');
        } else if (snapshot.hasError) {
          return Text('${snapshot.error}');
        }
        return const CircularProgressIndicator();
      },
    );
  }
}

    More about FutureBuilder

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  2. 0

    Running the build method cannot be delayed and this method cannot be asynchronous because that would block/delay the rendering of the UI making the app unresponsive.

    What you need to do is store the Future in the state and use FutureBuilder:

    class _WorterBuchState extends State<WorterBuch> with TickerProviderStateMixin {
Future<String>? wordPairFuture;
  
@override
void initState(){
  super.initState();
  load();
}

Future<void> load() async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  prefs.setString('key', 'value');
  wordPairFuture = "key : " + (prefs.getString('key') as String);
}
  @override
  Widget build(BuildContext context)  {
    if (wordPairFuture == null) {
      return const Placeholder(); // display some loading here
    }
    
    return FutureBuilder(
      future: wordPairFuture,
      builder: (context, snapshot) {
        // use `snapshot.hasData` to check if the `Future` is "ready"
        if (snapshot.hasData) print(snapshot.data)

        // ...
      }
    )
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