dart - 推送新屏幕后不显示默认后退按钮

Question

我从主屏幕上推送了一个新屏幕，它导航很流畅，还显示了后退按钮，但是现在我运行了该按钮，默认按钮没有显示在我的代码中。

我所做的唯一更改是我将主文件中的路由从 taskScreen() 更改为 task()。但这是必不可少的，因为我想从我的第二个屏幕创建更多路线，因此它必须返回一个 Material App。我怎样才能恢复默认的后退按钮？

我的代码:

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: DefaultTabController(length: 2,child: MyHomePage(title: '')),
      routes: <String, WidgetBuilder>{
       "/TaskScreen": (BuildContext context) => new task(), //CHANGED HERE 
      },
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

 @override
  Widget build(BuildContext context){

   return Scaffold(

     appBar: AppBar(
    ..
     ),
     body: ...
 }
}

我的第二个屏幕

class task extends StatelessWidget{
  @override
  Widget build(BuildContext context) {

    return MaterialApp(
        title: 'Task',
        home: new taskScreen(),
        routes: <String, WidgetBuilder>{
          "/Completed": (BuildContext context) => new Completed()
        }
    );
  }
}

class taskScreen extends StatefulWidget{
  @override
  taskState createState() => new taskState();
}

class taskState extends State<taskScreen> {

  @override
  Widget build(BuildContext context) {

  Column taskScreen = Column (...)

    return Scaffold(
      appBar: AppBar(
          title: Text('Task Screen')),
      body: taskScreen,
    );
  }

}

Answer 1

类名必须以大写字符开头。您的结构有误，MaterialApp 必须只有一次。 https://dart.dev/guides/language/language-tour