Flutter / Firebase 项目 - 是否“未处理的异常：空检查运算符用于空值”导致黑屏？

Question

我正在使用 firebase 开发一个 flutter 项目。我目前正在使用模拟 iPhone 在 MacBook 上进行开发（以防万一）。我可以运行我的应用程序，但是当这样做时它只是一个永远不会消失的白色空白屏幕，知道这发生在 Chrome 和模拟 Android 设备也是。查看 run window，我可以看到错误显示如下：

Launching lib/main.dart on iPhone 13 in debug mode...
Running Xcode build...
Xcode build done.                                           28.4s
Debug service listening on ws://127.0.0.1:61474/fF4XR-ozS5s=/ws
Syncing files to device iPhone 13...
[VERBOSE-2:ui_dart_state.cc(209)] Unhandled Exception: Null check operator used on a null value
#0      MethodChannel.binaryMessenger (package:flutter/src/services/platform_channel.dart:121:86)
#1      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:146:36)
#2      MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:329:12)
#3      MethodChannel.invokeListMethod (package:flutter/src/services/platform_channel.dart:342:41)
#4      MethodChannelFirebase._initializeCore (package:firebase_core_platform_interface/src/method_channel/method_channel_firebase.dart:31:37)
#5      MethodChannelFirebase.initializeApp (package:firebase_core_platform_interface/src/method_channel/method_channel_firebase.dart:73:13)
#6      Firebase.initializeApp (package:firebase_core/src/firebase.dart:42:47)
#7      main (package:we_rise/main.dart:8:18)
#8      _runMainZoned.<anonymous closure>.<anonymous closure> (dart:ui/hooks.dart:145:25)
#9      _rootRun (dart:async/zon<…>

因为我还是个新手，所以我不能完全理解哪里出了问题，或者我在这里看到的是什么。请在下面找到我的 main.dart 文件代码：

import 'package:firebase_core/firebase_core.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'database_config.dart';
import 'launch_page.dart';

void main() async {
  await Firebase.initializeApp(
    options: FirebaseOptions(
        apiKey: "foo",//"apiKey",
        appId: "foo",//"appId",
        messagingSenderId: "foo",//"messagingSenderId",
        projectId: "foo"),//"projectId"),
  );
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    SystemChrome.setPreferredOrientations(
      [DeviceOrientation.portraitUp, DeviceOrientation.portraitDown],
    );
    return MaterialApp(
      theme: ThemeData(
        brightness: Brightness.light,
        fontFamily: 'BookmanOldStyle',
      ),
      home: LaunchPage(),
    );
  }
}

我希望这是有用的。我真的不明白为什么它在应用程序加载时向我显示空白屏幕。我还阅读了，但我不认为我在我的代码中使用了 null 检查运算符。感谢任何帮助、建议和批评。

编辑：添加了颤振医生输出

flutter doctor 输出：

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 2.5.3, on macOS 12.0.1 21A559 darwin-arm, locale en-GB)
[✓] Android toolchain - develop for Android devices (Android SDK version 31.0.0)
[✓] Xcode - develop for iOS and macOS
[✓] Chrome - develop for the web
[✓] Android Studio (version 2020.3)
[✓] Connected device (2 available)

• No issues found!

flutter doctor -v 输出：

flutter doctor -v
[✓] Flutter (Channel stable, 2.5.3, on macOS 12.0.1 21A559 darwin-arm, locale en-GB)
    • Flutter version 2.5.3 at /Users/me/Documents/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 18116933e7 (3 months ago), 2021-10-15 10:46:35 -0700
    • Engine revision d3ea636dc5
    • Dart version 2.14.4

[✓] Android toolchain - develop for Android devices (Android SDK version 31.0.0)
    • Android SDK at /Users/me/Library/Android/sdk
    • Platform android-31, build-tools 31.0.0
    • Java binary at: /Applications/Android Studio.app/Contents/jre/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 13.2.1, Build version 13C100
    • CocoaPods version 1.11.2

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2020.3)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
       https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
       https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)

[✓] Connected device (2 available)
    • iPhone 13 (mobile) • C0D4EC95-07AF-46AB-A35E-F2B9F4437875 • ios            • com.apple.CoreSimulator.SimRuntime.iOS-15-2 (simulator)
    • Chrome (web)       • chrome                               • web-javascript • Google Chrome 97.0.4692.71

• No issues found!

Answer 1

您应该添加

WidgetsFlutterBinding.ensureInitialized()

到 Firebase 初始化之前的主函数。

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

  await Firebase.initializeApp(
    options: FirebaseOptions(
        apiKey: "foo",//"apiKey",
        appId: "foo",//"appId",
        messagingSenderId: "foo",//"messagingSenderId",
        projectId: "foo"),//"projectId"),
  );
  await DatabaseConfig.initFirebase();
  runApp(MyApp());
}

Answer 2

我认为其中之一应该有效。

确保您已正确初始化 firebase，即采取正确的步骤将 firebase 与您的项目集成。
在Firebase.initializeApp-
中添加一个名字

`等待Firebase.initializeApp(

name: "SecondaryApp",//**Add this line**
options: FirebaseOptions(
    apiKey: "foo",//"apiKey",
    appId: "foo",//"appId",
    messagingSenderId: "foo",//"messagingSenderId",
    projectId: "foo"),

);`

Answer 3

最好尝试“flutter 升级”，因为 2.5.3 不再是最新的稳定版本，它们现在是 2.8.1。然后确保您遵循了 each of the platform setup sections listed here.

下的所有说明（不折不扣）

如果您不得不运行在任何时候“彻底清理”或删除您的构建文件夹，请确保检查它们是否包含上面 link 中指定的必需包含。我在原文中看到 post 你说 flutterfire 在你的任何平台上都不工作，对我来说这表明库可能没有在每个平台的构建文件夹下完全配置。

Answer 4

对于所有遇到这个问题的人，对我有用的是在 Windows 版本上创建一个新项目（我正在使用 android studio）并在那里重新制作程序，您甚至可以复制和粘贴大部分内容。

在我看来，主要问题是我在 MacOS 上开发时没有 iPhone，因此，当它链接到我的开发者资料时，我无法运行 .

Flutter / Firebase 项目 - 是否“未处理的异常：空检查运算符用于空值”导致黑屏？

Flutter / Firebase project - Is `Unhandled Exception: Null check operator used on a null value` causing a blank screen?

null

android

ios

firebase

flutter