未處理的異常：輸入“未來”<QuerySnapshot> &#39; 不是 &#39;QuerySnapshot&#39; 類型的子類型

Question

未處理的異常：類型 'Future' 不是使用 firebase 的 flutter googlesignin 中類型 'QuerySnapshot' 的子類型。這一行有問題：final QuerySnapshot result=FirebaseFirestore.instance.collection('users').where('id',isEqualTo : user.uid).get();

它用於使用 firebase 登錄谷歌

import 'package:shared_preferences/shared_preferences.dart';
import 'package:fluttertoast/fluttertoast.dart';
import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_core/firebase_core.dart';
import 'home.dart';

import 'package:flutter_auth_buttons/flutter_auth_buttons.dart';
import 'package:flutter_signin_button/flutter_signin_button.dart';
class Login extends StatefulWidget {
  @override
  _LoginState createState() => _LoginState();
}

class _LoginState extends State<Login> {
  final FirebaseAuth firebaseAuth = FirebaseAuth.instance;
  final GoogleSignIn googleSignIn = new GoogleSignIn();
  SharedPreferences preferences;
  bool loading = false;
  bool isLogedIn = false;

  @override
  void initState() {
    super.initState();
    isSignedIn();
  }

  void isSignedIn() async {
    setState(() {
      loading = true;
    });
    preferences = await SharedPreferences.getInstance();
    isLogedIn = await googleSignIn.isSignedIn();
    if (isLogedIn) {
      Navigator.pushReplacement(
          context, MaterialPageRoute(builder: (context) => HomePage()));
    }
    setState(() {
      loading = false;
    });
  }

  Future<Null> handleSignIn() async{
    preferences = await SharedPreferences.getInstance();
    final GoogleSignInAccount googleUser = await googleSignIn.signIn();
    final GoogleSignInAuthentication googleSignInAuthentication = await googleUser.authentication;
    AuthCredential credential = GoogleAuthProvider.credential(idToken: googleSignInAuthentication.idToken, accessToken: googleSignInAuthentication.accessToken);
    //final UserCredential userCredential = await firebaseAuth.signInWithCredential(credential);
    //final User user = userCredential.user;
    User user = (await firebaseAuth.signInWithCredential(credential)).user;```


  if(user!=null)
      {
         final QuerySnapshot result=FirebaseFirestore.instance.collection('users').where('id',isEqualTo: user.uid).get();
         List<DocumentSnapshot> documents= result.docs;
        if(documents.length==0)
          {
            //insert user to collection
             FirebaseFirestore.instance.collection('users').doc(user.uid).set({
                "id":user.uid,
             "username":user.displayName,
             "photourl":user.photoURL});
             await preferences.setString("id", user.uid);
             await preferences.setString("username", user.displayName);
             await preferences.setString("photourl", user.photoURL);
          }
        else{
         // await preferences.setString("id",documents[0].data['id']);
          //await preferences.setString("photourl",documents[0]['photourl']);
          //await preferences.setString("username",documents[0]['username']);
          await preferences.setString("id", documents[0].data()['id']);
          await preferences.setString("username", documents[0].data()['username']);
          await preferences.setString("photourl", documents[0].data()['photoUrl']);

        }
        Fluttertoast.showToast(msg: "Login Was successful");
        setState(() {
          loading=false;
        });
        Navigator.push(context, MaterialPageRoute(builder: (context)=>HomePage()));
      }else{
      Fluttertoast.showToast(msg: "Login Failed");
      setState(() {
        loading=false;
      });
    }
  }
    @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stack(
        children:<Widget> [
          Center(
            child: FlatButton(
              color: Colors.red,
          onPressed: (){handleSignIn();},child: Text("sigin",style: TextStyle(color: Colors.white),),

      )
            ),
      Visibility(
        visible: loading ?? true,

          child: Center(
        child: Container(
      alignment: Alignment.center,
      color: Colors.white.withOpacity(0.8),
          child: CircularProgressIndicator(
            valueColor: AlwaysStoppedAnimation<Color>(Colors.red),
          ),

        )

      )
          )
        ],
      ),
    );
  }


}```

Answer 1

get()返回Future<QuerySnapshot> ，因此您需要執行以下操作：

final QuerySnapshot result= await FirebaseFirestore.instance.collection('users').where('id',isEqualTo: user.uid).get();

https://dart.dev/codelabs/async-await