dart - 为什么 "Navigator operation requested with a context that does not include a Navigator"

Question

我知道如何解决问题，但不知道为什么会这样:

我有一个有 2 个屏幕的应用:

这个 main.dart:

import 'package:flutter/material.dart';
import 'HomeActivity.dart';

void main() {
  runApp(App());
}

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new HomeActivity();
  }
}

HomeActivity.Dart:

import 'package:flutter/material.dart';
import 'AddGameActivity.dart';

class HomeActivity extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new Scaffold(
        appBar: AppBar(title: new Text("Home")),
        floatingActionButton: FloatingActionButton(
            onPressed: () => Navigator.push(context, new MaterialPageRoute(builder: (context) => new AddGameActivity())),
            child: new Icon(Icons.add))),
    );
  }

所以这里我有一个带有 FAB 按钮的屏幕，可以将我导航到 AddGameActivity，当我按下 FAB 按钮时，这是错误消息:

navigator operation requested with a context that does not include a Navigator

现在为了解决这个问题，我将 MaterialApp 添加到 main.dart 并将其从 HomeActivity.dart 中删除，如下所示:

主 Dart :

import 'package:flutter/material.dart';
import 'HomeActivity.dart';

void main() {
  runApp(App());
}

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(home: HomeActivity());
    }
}

首页事件:

import 'package:flutter/material.dart';
import 'AddGameActivity.dart';

class HomeActivity extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        appBar: AppBar(title: new Text("Home")),
        floatingActionButton: FloatingActionButton(
            onPressed: () => Navigator.push(context, new MaterialPageRoute(builder: (context) => new AddGameActivity())),
            child: new Icon(Icons.add)));
  }
}

在这种情况下，当我在 main.dart 中添加 Material 应用程序时，它可以正常工作，没有任何问题。

所以我的问题是为什么会这样？在这两种方式中，我都有一个 Material 应用程序，其中有一个 Scaffold !

Answer 1

如评论中所述，此问题似乎与这篇文章重复:"Navigator operation requested with a context that does not include a Navigator"

之所以报错是因为Navigator无法从MaterialApp访问Navigator。要解决此问题，您可以声明 MaterialApp 并初始化 HomeActivity - 就像您正在做的那样，或者您可以在 HomeActivity 中初始化 MaterialApp 之后添加一个 Builder。

import 'package:flutter/material.dart';

void main() {
  runApp(App());
}

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return HomeActivity();
  }
}

class HomeActivity extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      // call Builder to access Navigator from MaterialApp
      home: Builder(
        builder: (context) => Scaffold(
            appBar: AppBar(title: Text("Home")),
            floatingActionButton: FloatingActionButton(
                onPressed: () => Navigator.push(
                    context,
                    new MaterialPageRoute(
                        builder: (context) => AddGameActivity())),
                child: new Icon(Icons.add))),
      ),
    );
  }
}

class AddGameActivity extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
          appBar: AppBar(title: Text("AddGame")),
          floatingActionButton: FloatingActionButton(
              onPressed: () => Navigator.push(
                  context,
                  new MaterialPageRoute(
                      builder: (context) => new AddGameActivity())),
              child: new Icon(Icons.add)));
  }
}