使用路由时在空值上使用的空检查运算符

Question

我正在重构我的应用程序以使用 this guide 支持本地化。有一次我需要从使用 home 属性切换到使用 initialRoute 和 routes。相关代码片段如下所示：

return PlatformApp(
            material: (_, platform) => MaterialAppData(theme: materialThemeData),
            cupertino: (_, platform) => CupertinoAppData(theme: cupertinoTheme),
            onGenerateTitle: (context) {
              return AppLocalizations.of(context).appTitle;
            },
            localizationsDelegates: [
              AppLocalizations.delegate,
              GlobalMaterialLocalizations.delegate,
              GlobalWidgetsLocalizations.delegate,
              GlobalCupertinoLocalizations.delegate,
            ],
            supportedLocales: [
              const Locale('de', ''),
              const Locale('en', ''),
            ],
            initialRoute: '/',
            routes: {
              '/': (context) {
                return MyHomeScreen(title: AppLocalizations.of(context).appTitle);
              },
            },
            // home:MyHomeScreen(title: 'Static Title'),
          );
        }

当我在 iOS 上尝试运行时，会产生以下错误：

======== Exception caught by widgets library =======================================================
The following _CastError was thrown building Builder(dirty):
Null check operator used on a null value

The relevant error-causing widget was: 
  CupertinoApp file:///Users/user/Development/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_platform_widgets-1.7.1/lib/src/platform_app.dart:673:14
When the exception was thrown, this was the stack: 
#0      _WidgetsAppState._onGenerateRoute.<anonymous closure> (package:flutter/src/widgets/app.dart:1196:48)
#1      CupertinoPageRoute.buildContent (package:flutter/src/cupertino/route.dart:359:55)
#2      CupertinoRouteTransitionMixin.buildPage (package:flutter/src/cupertino/route.dart:227:26)
#3      _ModalScopeState.build.<anonymous closure>.<anonymous closure> (package:flutter/src/widgets/routes.dart:840:53)
#4      Builder.build (package:flutter/src/widgets/basic.dart:7555:48)
...
====================================================================================================

我为这个应用程序使用 flutter_platform_widgets，并且我已经尝试了以下操作：

运行 Android 版本，看看是否发生同样的情况：大致相同的情况发生，只是 material 包抛出错误而不是 cupertino
用静态文本替换本地化标题，但结果是一样的

看来我遗漏了一些明显的东西（我是 Flutter 的新手）。当我注释掉 initialRoute 和 routes 并改用 home 时，它工作正常 - 但显然没有本地化。那么，我在这里缺少什么？

Flutter 医生输出：

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 2.0.6, on macOS 11.2.3 20D91 darwin-x64, locale en-CH)
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
[✓] Xcode - develop for iOS and macOS
[✓] Chrome - develop for the web
[✓] Android Studio (version 4.2)
[✓] Connected device (4 available)

• No issues found!

Answer 1

@puelo 的评论帮助我解决了这个问题。

问题是在初始化过程的早期我初始化了 Firebase 应用程序，并且根据结果我提供了不同的应用程序小部件。如果 firebase 仍在加载或抛出错误，我展示了一个简单的应用程序，其中设置了 home 属性 - 这就是问题所在。现在我更改了它，以便应用程序始终相同，但加载和错误状态是通过导航来处理的。

使用路由时在空值上使用的空检查运算符

Null check operator used on a null value when using routes

flutter

flutter-navigation

flutter-routes

flutter-localizations