使用命名路由时对空值使用空值检查运算符

Question

在我切换到named routes 后，我收到此错误，我的应用在使用MaterialPageRoute 时可以正常工作：

ma​​in.dart：

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(
    MultiProvider(
      providers: [
        ChangeNotifierProvider(create: (context) => ClassA()),
        ChangeNotifierProvider(
            create: (context) => ClassB()),
      ],
      child: MyApp(),
    ),
  );
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
        future: Firebase.initializeApp(),
        builder: (context, snapshot) {
          if (snapshot.hasError) {
            return ...
          }
          if (snapshot.connectionState == ConnectionState.done) {
              return MaterialApp(
                debugShowCheckedModeBanner: false,
                title: 'App Title',
                initialRoute: '/',
                routes: {
                  '/': (context) => Wrapper(),
                  'somePage/': (context) => SomePage(),
                },
              );
          }
          //else ...
          return ... ;
        });
  }
}

错误信息：

The following _CastError was thrown building Builder(dirty):
Null check operator used on a null value

The relevant error-causing widget was: 
MaterialApp file:///.../lib/main.dart:40:20
When the exception was thrown, this was the stack: 
#0      _WidgetsAppState._onGenerateRoute.<anonymous closure> (package:flutter/src/widgets/app.dart:1196:48)
#1      MaterialPageRoute.buildContent (package:flutter/src/material/page.dart:54:55)
#2      MaterialRouteTransitionMixin.buildPage (package:flutter/src/material/page.dart:107:27)
#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)

颤振医生：

Doctor summary (to see all details, run flutter doctor -v):
[√] Flutter (Channel stable, 2.0.2, on Microsoft Windows [Version 10.0.19042.867], locale en-US)
[√] Android toolchain - develop for Android devices (Android SDK version 30.0.1)
[√] Chrome - develop for the web
[√] Android Studio (version 4.1.0)
[√] VS Code (version 1.52.1)
[√] Connected device (3 available)

• No issues found!

奇怪的是，该应用程序在多次热重启后工作，然后热重启崩溃。

Answer 1

不确定“为什么”，但您必须将“根”小部件从 FutureBuilder 更改为注册命名路由的 MaterialApp。

与您具有相同的代码结构和相同的错误。我将我的 MaterialApp 作为runApp 的参数，一切都很好¯_(ツ)_/¯

Answer 2

我遇到了和你一样的情况，重新启动应用解决了这个问题。

Answer 3

您不能同时提供 initialRoute 和 '/'，

Route '/' 已经是initialRoute 去掉initialRoute就行了