Flutter：在无状态小部件中调用异步方法

Question

I have a Async method that I want to call in a stateless widget. While running it it says

Future dynamic Is not a sub type of widget

And then it shows the result after some seconds.How can I stop it? This is my method

    var onvalue = await Firestore.instance
        .collection("userdata")
        .document(user.uid)
        .get();
    if (onvalue.exists) {
      return Navigator.pushReplacement(context,
        MaterialPageRoute(builder: (context) => mainhomepage()),);
    }
    else {
      print("register");
      return  Navigator.pushReplacement(context,
        MaterialPageRoute(builder: (context) => Register()),);
    }
 }

And my main body

Widget build(BuildContext context) {
    var user = Provider.of<User>(context);
    //return either home or authenticate
    return MaterialApp (
        home: user != null?check(user)//Calling the function
            :app()
    );
  }

Answer 1

You can use Futurebuilder.

Widget build(BuildContext context) {
    var user = Provider.of<User>(context);
    //return either home or authenticate
    return MaterialApp (
        home: user != null?
              FutureBuilder(
              future: check(user),
              builder: (_, snapshot) {
                if (snapshot.connectionState == ConnectionState.done) {
                  return Text(snapshot.data);
                } else {
                  return CircularProgressIndicator();
                }
              },
            )
            :app()
          );
      }