无法在新页面路由小部件中访问提供者

Question

我无法访问推送到当前导航器的小部件中的提供程序：

import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart';
import 'package:provider/provider.dart';


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

class MyModel with ChangeNotifier {
  String a = 'Test1';
  String b = 'Test2';
}

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

    return MaterialApp(
        title: 'Flutter Demo',
        home: ChangeNotifierProvider(
            create: (context) => MyModel(),
            child: MyHomePage()
        )
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);

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

class _MyHomePageState extends State<MyHomePage> {

  @override
  Widget build(BuildContext context) {    

    return Consumer<MyModel>(
        builder: (context, myModel, child) =>
            Scaffold(
              appBar: AppBar(
                title: Text(myModel.a),
              ),
              floatingActionButton: FloatingActionButton(
                onPressed: () =>
                    Navigator.of(context).push(
                        PageRouteBuilder(
                            pageBuilder: (context, animation, secondaryAnimation) => Page2(),
                        ),
                    ),
                tooltip: 'Press',
                child: Icon(Icons.add),
              ),
            )
    );
  }
}

class Page2 extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    var myModel = Provider.of<MyModel>(context); // A

    return Scaffold(
              appBar: AppBar(
                title: Text(myModel.b),
              ),
            );
  }
}

我收到此错误：

The following ProviderNotFoundException was thrown building Page2(dirty):
Error: Could not find the correct Provider<MyModel> above this Navigator Widget

问题似乎是 Page2 小部件中的 BuildContext 对象与与提供者关联的 BuildContext 不同。如果我将原始上下文的引用传递给 Page2 并在 (A) 点使用它，则一切正常，但这似乎不是解决此问题的好方法。

我在这里尝试了解决方案，将其Navigator.of(context, rootNavigator: true).context用作buildPage2 方法中的上下文，但我仍然遇到相同的异常。

Answer 1

您必须在根小部件中传递提供程序，以便您可以在导航到模型不可用的另一个页面时从任何位置访问，因此您必须将提供程序传递给 MaterialApp 的父级

 import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart';
import 'package:provider/provider.dart';

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

class MyModel with ChangeNotifier {
  String a = 'Test1';
  String b = 'Test2';
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
      create: (context) => MyModel(),
      child: MaterialApp(title: 'Flutter Demo', home: MyHomePage()),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);

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

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Consumer<MyModel>(
        builder: (context2, myModel, child) => Scaffold(
              appBar: AppBar(
                title: Text(myModel.a),
              ),
              floatingActionButton: FloatingActionButton(
                onPressed: () => Navigator.of(context).push(
                  PageRouteBuilder(
                    pageBuilder: (context, animation, secondaryAnimation) =>
                        Page2(),
                  ),
                ),
                tooltip: 'Press',
                child: Icon(Icons.add),
              ),
            ));
  }
}

class Page2 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    var myModel = Provider.of<MyModel>(context); // A

    return Scaffold(
      appBar: AppBar(
        title: Text(myModel.b),
      ),
    );
  }
}