使用路由时对空值使用的空检查运算符

问题描述

我正在重构我的应用以支持使用 this guide 的本地化。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'),);
        }

当我尝试在 iOS 上运行它时会产生以下错误：

======== 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)
...
====================================================================================================

我为此应用使用了 flutter_platform_widgets，并且已经尝试了以下操作：

运行Android版本，看看是否会发生同样的情况：大致相同，只是材质包抛出错误而不是cupertino
用静态文本替换本地化的标题，但结果是一样的

看起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 并使用 home 时，它工作正常 - 但显然没有本地化。那么，我在这里错过了什么？

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!

解决方法

@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 仍在加载或引发错误，我会展示一个带有 home 属性集的简单应用程序 - 这就是问题所在。现在我更改了它，以便应用程序始终相同，但加载和错误状态由导航处理。

flutter-localizations flutter-navigation flutter-routes