Flutter: Why setState(( ) { }) set data again and again
The purpose of setState is to tell the framework that a variable in the state has changed and the widget needs to be rebuilt to reflect that change. So calling setState calls the build function again, which in your case recalls your Future, which calls setState again, which triggers build and so on.
To fix this you should call the Future in initState, and use a FutureBuilder to display the data when it's ready.
Example:
class _SampleState extends State<Sample> { Firestore db = Firestore.instance; Future databaseFuture; @override void initState() { databaseFuture = db.collection('share').document('0').get() } @override Widget build(BuildContext context) { return FutureBuilder( future: databaseFuture, builder: (context, snapshot) { if(!snapshot.hasData) { return CircularProgressIndicator(); } var message = snapshot.data.data['message']; print(message); var appLink = snapshot.data.data['appLink']; return Text('$message $appLink'); } ), }}