flutter - Flutter Provider嵌套导航

Question

我在提供程序和导航上有问题。

我有一个带有对象列表的HomeScreen。当您单击一个对象时，我使用选项卡导航导航到DetailScreen。此DetailScreen包裹在ChangenotifierProvider中，后者提供了ViewModel
现在，当我使用Navigator.of(context).push(EditScreen)导航到另一个屏幕时，无法访问ViewModel中的EditScreen引发以下错误

════════ Exception caught by gesture ═══════════════════════════════════════════
The following ProviderNotFoundException was thrown while handling a gesture:
Error: Could not find the correct Provider<ViewModel> above this EditScreen Widget

这是我尝试实现的目标的简单概述

Home Screen
 - Detail Screen (wrapped with ChangeNotifierProvider)
   - Edit Screen
     - access provider from here

我知道是什么问题。我正在堆栈上推一个新屏幕，并且更改通知器不再可用。
我考虑过要在我的应用程序顶部创建一个详细信息存储库，该存储库包含DetailView的所有ViewModel。

我知道我可以将ChangeNotifier包裹在我的MaterialApp周围，但是我不希望那样做，或者因为我不知道我需要哪个Detail-ViewModel而不能这样做。我想要列表中的每个项目都有一个ViewModel

我真的不知道什么是解决此问题的最佳方法。谢谢大家的帮助

这是一个快速的示例应用程序:

This is a picture of the image tree

import 'package:flutter/material.dart';
import 'package:provider/provider.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(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Center(
            child: RaisedButton(
      child: Text("DetailView"),
      onPressed: () => Navigator.of(context).push(MaterialPageRoute(
          builder: (context) => ChangeNotifierProvider(
              create: (_) => ViewModel(), child: DetailScreen()))),
    )));
  }
}

class DetailScreen extends StatelessWidget {
  const DetailScreen({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Center(
      child: RaisedButton(
        child: Text("EditScreen"),
        onPressed: () => Navigator.of(context)
            .push(MaterialPageRoute(builder: (context) => EditScreen())),
      ),
    ));
  }
}

class EditScreen extends StatelessWidget {
  const EditScreen({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: RaisedButton(
            child: Text("Print"),
            onPressed: () =>
                Provider.of<ViewModel>(context, listen: false).printNumber()),
      ),
    );
  }
}

class ViewModel extends ChangeNotifier {
  printNumber() {
    print(2);
  }
}

Answer 1

为了能够跨导航访问提供者，您需要在MaterialApp之前提供它，如下所示

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

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
      create: (_) => ViewModel(),
      child: MaterialApp(
        title: 'Flutter Demo',
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: MyHomePage(),
      ),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Center(
            child: RaisedButton(
      child: Text("DetailView"),
      onPressed: () => Navigator.of(context).push(
        MaterialPageRoute(
          builder: (context) => DetailScreen(),
        ),
      ),
    )));
  }
}

class DetailScreen extends StatelessWidget {
  const DetailScreen({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Center(
      child: RaisedButton(
        child: Text("EditScreen"),
        onPressed: () => Navigator.of(context)
            .push(MaterialPageRoute(builder: (context) => EditScreen())),
      ),
    ));
  }
}

class EditScreen extends StatelessWidget {
  const EditScreen({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: RaisedButton(
            child: Text("Print"),
            onPressed: () =>
                Provider.of<ViewModel>(context, listen: false).printNumber()),
      ),
    );
  }
}

class ViewModel extends ChangeNotifier {
  printNumber() {
    print(2);
  }
}