您可以使用onGenerateRoute，请参见下面的代码段，工作演示和完整代码

代码段

return MaterialApp(
        title: 'Flutter Demo',theme: ThemeData(         
          primarySwatch: Colors.blue,),initialRoute: '/',onGenerateRoute: (RouteSettings settings) {
          switch (settings.name) {
            case "/":
              return MaterialPageRoute(
                  builder: (context) => MyHomePage(
                        title: "Demo",));
            case "/dialog":
              return MaterialPageRoute(
                  builder: (context) => YourDialog(),fullscreenDialog: true);
          }
        });
  }

Navigator.pushNamed(context,'/dialog');

工作演示

完整代码

import 'package:flutter/material.dart';

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',theme: ThemeData(
          // This is the theme of your application.
          //
          // Try running your application with "flutter run". You'll see the
          // application has a blue toolbar. Then,without quitting the app,try
          // changing the primarySwatch below to Colors.green and then invoke
          // "hot reload" (press "r" in the console where you ran "flutter run",// or simply save your changes to "hot reload" in a Flutter IDE).
          // Notice that the counter didn't reset back to zero; the application
          // is not restarted.
          primarySwatch: Colors.blue,fullscreenDialog: true);
          }
        });
  }
}

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

  // This widget is the home page of your application. It is stateful,meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    Navigator.pushNamed(context,'/dialog');

    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State,which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(),then the build method would not be
      // called again,and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called,for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast,so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method,and use it to set our appbar title.
        title: Text(widget.title),body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default,it sizes itself to fit its
          // children horizontally,and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console,choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio,or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,children: <Widget>[
            Text(
              'You have pushed the button this many times:',Text(
              '$_counter',style: Theme.of(context).textTheme.display1,],floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,tooltip: 'Increment',child: Icon(Icons.add),// This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

class YourDialog extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Dialog Magic'),body: Text("It's a Dialog!"),);
  }
}

在你的孩子上 使用

return Scaffold(
   appbar: Appbar(
     title: Text("Fullscreen")
   ),body: Container(
       width: MediaQuery.of(context).size.width,height: MediaQuery.of(context).size.height
   )
);