添加到pubspec.yaml firebase_core: 添加到main.dart 导入的包:firebase_core / firebase_core.dart '; 无效main() async { WidgetsFlutterBinding.ensureInitialized (); 等待Firebase.initializeApp (); runApp (MyApp ()); ｝

在大多数情况下，此问题是在将项目从旧的Flutter版本升级到零安全后观察到的。应该检查以下内容:

确保在pubspecc .yaml中有firebase-core

导入firebase核心:

import 'package:firebase_core/firebase_core.dart';

在任何调用之前Init Firebase -最好在main内部。Dart，因此它在任何其他实现之前执行:

WidgetsFlutterBinding.ensureInitialized();
await Firebase.initializeApp(
  options: DefaultFirebaseOptions.currentPlatform,
);

来自官方文件。

自2020年8月17日起

所有Firebase版本都已更新，现在你必须在使用任何Firebase产品之前调用Firebase. initializeapp()，例如:

首先，所有Firebase产品现在都依赖于firebase_core版本(0.5.0+)，因此您需要将其添加到pubspec中。yaml文件:

dependencies:
  flutter:
    sdk: flutter
  firebase_core : ^0.5.0
  # cloud_firestore: ^0.14.0 other firebase dependencies

然后你必须调用Firebase.initializeApp():

第一个例子

import 'package:flutter/material.dart';

// Import the firebase_core plugin
import 'package:firebase_core/firebase_core.dart';

void main() {
  runApp(App());
}

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      // Initialize FlutterFire
      future: Firebase.initializeApp(),
      builder: (context, snapshot) {
        // Check for errors
        if (snapshot.hasError) {
          return SomethingWentWrong();
        }

        // Once complete, show your application
        if (snapshot.connectionState == ConnectionState.done) {
          return MyAwesomeApp();
        }

        // Otherwise, show something whilst waiting for initialization to complete
        return Loading();
      },
    );
  }
}

Firestore的第二个例子:

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';
import 'package:firebase_core/firebase_core.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: FirstRoute(title: 'First Route'),
    );
  }
}

class FirstRoute extends StatefulWidget {
  FirstRoute({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _FirstRouteState createState() => _FirstRouteState();
}

class _FirstRouteState extends State<FirstRoute> {
  @override
  void initState() {
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("test"),
        ),
        body: FutureBuilder(
          future: getData(),
          builder: (context, AsyncSnapshot<DocumentSnapshot> snapshot) {
            if (snapshot.connectionState == ConnectionState.done) {
              return Column(
                children: [
                  Container(
                    height: 27,
                    child: Text(
                      "Name: ${snapshot.data.data()['name']}",
                      overflow: TextOverflow.fade,
                      style: TextStyle(fontSize: 20),
                    ),
                  ),
                ],
              );
            } else if (snapshot.connectionState == ConnectionState.none) {
              return Text("No data");
            }
            return CircularProgressIndicator();
          },
        ));
  }

  Future<DocumentSnapshot> getData() async {
    await Firebase.initializeApp();
    return await FirebaseFirestore.instance
        .collection("users")
        .doc("docID")
        .get();
  }
}

第三个例子:

在initState()中初始化它，然后调用setState()，后者将调用build()方法。

  @override
  void initState() {
    super.initState();
    Firebase.initializeApp().whenComplete(() { 
      print("completed");
      setState(() {});
    });
  }

第四个例子:

在调用WidgetsFlutterBinding.ensureInitialized()后在main()方法中初始化它;

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

注意:你只需要调用initializeApp()一次

彼得的答案是完美的!但如果您的代码中仍然出现错误，并遵循Flutter Firebase代码实验室，请注意，这些教程截至2020年8月已过时，尚未更新。

你需要做很多其他的改变，比如:

将.data替换为.data() 用update替换updateData

对我来说，问题是我初始化它没有“等待”:

void main() async {
    WidgetsFlutterBinding.ensureInitialized();
    Firebase.initializeApp();

正确的做法是:

void main() async {
    WidgetsFlutterBinding.ensureInitialized();
    await Firebase.initializeApp();

自2017年8月以来，所有Firebase服务都已更新，因此在使用任何Firebase产品之前，您必须在主程序中调用Firebase. initializeapp()，例如:

如果您希望在flutter应用程序中使用firebase_core插件，则在您的pubspec中。Yaml文件添加firebase_core如下所示

dependencies:
  flutter:
    sdk: flutter
  firebase_core: ^1.19.1

然后调用Firebase.initializeApp():在你的应用中。如下所示:

import 'package:firebase_core/firebase_core.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}