错误：未为类型'DocumentSnapshot'定义运算符'[]'

Question

代码运行正常，但是当我更新依赖项时，开始出现以下错误：

1. 错误：未为类型'DocumentSnapshot'定义运算符'[]'
2. 错误：表达式不能求值为函数，因此无法调用它。 （invocation_of_non_function_expression

这是代码：

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:fluttertoast/fluttertoast.dart';
import 'package:google_sign_in/google_sign_in.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:za/pages/signup.dart';
import 'home.dart';


class Login extends StatefulWidget {
  @override
  _LoginState createState() => _LoginState();
}

class _LoginState extends State<Login> {
  final GoogleSignIn googleSignIn = new GoogleSignIn();
  final FirebaseAuth firebaseAuth = FirebaseAuth.instance;
  final _formKey = GlobalKey<FormState>();
  TextEditingController _emailTextController = TextEditingController();
  TextEditingController _passwordTextController = TextEditingController();
  SharedPreferences preferences;
  bool loading = false;
  bool islogedin = false;
  bool hidepass = true;

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

  void isSignedIn() async {
    setState(() {
      loading = true;
    });


    await firebaseAuth.currentUser().then((user){
      if (user!=null){
        setState(() => islogedin= true);
      }
    });
    if (islogedin == true) {
      Navigator.pushReplacement(
          context, MaterialPageRoute(builder: (context) => HomePage()));
    }
    setState(() {
      loading = false;
    });
  }

  Future handleSignIn() async {
    preferences = await SharedPreferences.getInstance();
    setState(() {
      loading = true;
    });

    final GoogleSignInAccount googleUser = await googleSignIn.signIn();
    final GoogleSignInAuthentication googleAuth =
        await googleUser.authentication;

    final AuthCredential credential = GoogleAuthProvider.getCredential(
      accessToken: googleAuth.accessToken,
      idToken: googleAuth.idToken,
    );
    User firebaseUser =
        (await firebaseAuth.signInWithCredential(credential)).user;

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

      Fluttertoast.showToast(msg: "Login failed");
    }
  }

Answer 1

1. DocumentSnapshot没有[]运算符，正如错误明确指出的那样。它具有data字段。

替换此代码：

    await preferences.setString("id", documents[0]['id']);
    await preferences.setString("username", documents[0]['username']);
    await preferences.setString("photoUrl", documents[0]['photoUrl']);

与此：

    await preferences.setString("id", documents[0].data['id']);
    await preferences.setString("username", documents[0].data['username']);
    await preferences.setString("photoUrl", documents[0].data['photoUrl']);

1. 根据消息来源：

  /// Returns the current [User] if they are currently signed-in, or `null` if
  /// not.
  ///
  /// You should not use this getter to determine the users current state,
  /// instead use [authStateChanges], [idTokenChanges] or [userChanges] to
  /// subscribe to updates.
  User get currentUser {
    if (_delegate.currentUser != null) {
      return User._(this, _delegate.currentUser);
    }

    return null;
  }

Answer 2

尝试await preferences.setString("username", documents[0].data()['username']);

顺便说一句，您是否更新了Firebase软件包？如果是，请点击此链接以检查更新的更改https://firebase.flutter.dev/docs/migration/

Answer 3

固定1，我更改了

await preferences.setString("id", documents[0]['id']);
await preferences.setString("username", documents[0]['username']);
await preferences.setString("photoUrl", documents[0]['photoUrl']);

到

await preferences.setString("id", documents[0].data()['id']);
await preferences.setString("username", documents[0].data()['username']);
await preferences.setString("photoUrl", documents[0].data()['photoUrl']);

显然，现在可以通过 data（）方法来通过 data 获取器获取快照数据。

我只剩下错误 在

上

await firebaseAuth.currentUser().then((user){
      if (user!=null){
        setState(() => islogedin= true);
      } 

根据文档（https://firebase.flutter.dev/docs/migration/），现在可以通过currentUser getter同步通过currentUser（）访问当前用户。