Firebase.initializeApp() 给出错误：空值检查运算符用于空值

Posted 2023-02-22

【中文标题】Firebase.initializeApp() 给出错误：空值检查运算符用于空值

【英文标题】：Firebase.initializeApp() gives error: Null check operator used on a null value

【发布时间】：2021-09-01 17:57:34

【问题描述】：

运行这个

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

void main() async 
   await Firebase.initializeApp();
  runApp(MyApp());


class MyApp extends StatelessWidget 
  @override
  Widget build(BuildContext context) 
    return MaterialApp(
      home: ThePage(),
    );
  


class ThePage extends StatelessWidget 
  const ThePage(Key? key) : super(key: key);

  @override
  Widget build(BuildContext context) 
    return Scaffold(          
    );
  

给出用于空值的空检查运算符并指出行Firebase.initializeApp()。 我也试过flutter clean。

以及堆栈跟踪中的错误

E/flutter (31894): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: Null check operator used on a null value
E/flutter (31894): #0      MethodChannel.binaryMessenger
package:flutter/…/services/platform_channel.dart:142
E/flutter (31894): #1      MethodChannel._invokeMethod
package:flutter/…/services/platform_channel.dart:148
E/flutter (31894): #2      MethodChannel.invokeMethod
package:flutter/…/services/platform_channel.dart:331
E/flutter (31894): #3      MethodChannel.invokeListMethod
package:flutter/…/services/platform_channel.dart:344
E/flutter (31894): #4      MethodChannelFirebase._initializeCore
package:firebase_core_platform_interface/…/method_channel/method_channel_firebase.dart:30
E/flutter (31894): #5      MethodChannelFirebase.initializeApp
package:firebase_core_platform_interface/…/method_channel/method_channel_firebase.dart:77
E/flutter (31894): #6      Firebase.initializeApp
package:firebase_core/src/firebase.dart:41
E/flutter (31894): #7      main
package:firebasetests/main.dart:5
E/flutter (31894): #8      _runMainZoned.<anonymous closure>.<anonymous closure> (dart:ui/hooks.dart:142:25)
E/flutter (31894): #9      _rootRun (dart:async/zone.dart:1354:13)
E/flutter (31894): #10     _CustomZone.run (dart:async/zone.dart:1258:19)
E/flutter (31894): #11     _runZoned (dart:async/zone.dart:1789:10)
E/flutter (31894): #12     runZonedGuarded (dart:async/zone.dart:1777:12)
E/flutter (31894): #13     _runMainZoned.<anonymous closure> (dart:ui/hooks.dart:138:5)
E/flutter (31894): #14     _delayEntrypointInvocation.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:283:19)
E/flutter (31894): #15     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:184:12)

这是错误的堆栈跟踪，在 main 中删除 Firebase.initializeApp() 后它运行正常。

【参考方案1】：

在 android/app/build.gradle 中添加这一行，这对我有用

应用插件：'com.google.gms.google-services'

【参考方案2】：

使用@mkobuolys 提到的代码行。

我在 Visual Studio Code 中遇到了同样的问题，但它没有显示任何有关错误的详细信息，但 Android Studio 显示了。

如果有人感兴趣，这里是异常消息中最重要的信息：

如果您正在运行应用程序并需要访问二进制文件 runApp() 之前的 messenger 已被调用（例如，在 插件初始化），那么你需要显式调用 WidgetsFlutterBinding.ensureInitialized() 首先。如果你正在运行一个 测试，可以拨打TestWidgetsFlutterBinding.ensureInitialized() 作为测试的main() 方法中的第一行来初始化 绑定。

【参考方案3】：

您应该在主函数中添加WidgetsFlutterBinding.ensureInitialized();：

void main() async 
  WidgetsFlutterBinding.ensureInitialized(); // Add this

  await Firebase.initializeApp();
  runApp(MyApp());

对于 Firebase 初始化，需要使用 Flutter Platform Channels 访问本机代码。为此，您需要确保已初始化 Flutter 引擎绑定。