Question

大家好

我是使用 Riverpod 的新手，我有一个计数器应用程序，当点击 FAB 按钮时，它会将计数器增加 1。这在使用 Riverpod ChangeNotifierProvider 时效果很好。我目前遇到的问题是当我点击另一个将用户带到第二个屏幕的按钮时，在第二个屏幕中保留计数器的状态。

下面是我的代码

main.dart

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:flutter_riverpod_app/counter.dart';
import 'package:flutter_riverpod_app/second_screen.dart';

final counterProvider = ChangeNotifierProvider<Counter>((ref) => Counter());

void main() {
  runApp(ProviderScope(
    child: 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,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        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: Consumer(builder: (context, watch, _) {
          final count = watch(counterProvider);
          return Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                'You have pushed the button this many times:',
              ),
              Text(
                '${count.count}',
                style: Theme.of(context).textTheme.headline4,
              ),
              FlatButton(
                  onPressed: () {
                    Navigator.push(
                        context,
                        MaterialPageRoute(
                            builder: (BuildContext context) => SecondScreen()));
                  },
                  child: Text('Go to second screen'))
            ],
          );
        }),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => context.read(counterProvider).updateCount(),
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

second_screen.dart

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:flutter_riverpod_app/counter.dart';

final counterProvider = ChangeNotifierProvider<Counter>((ref) => Counter());

class SecondScreen extends ConsumerWidget {
  @override
  Widget build(BuildContext context, watch) {
    final counter = watch(counterProvider);
    return Scaffold(
      appBar: AppBar(
        title: Text('Second Screen'),
      ),
      body: Center(
        child: Text('${counter.count}', style: TextStyle(fontSize: 30,),),
      ),
    );
  }
}

计数器.dart

import 'package:flutter/foundation.dart';

class Counter extends ChangeNotifier {
  int count = 0;

  updateCount() {
    count++;
    notifyListeners();
  }
}

我真的不知道如何在第二个屏幕上获取计数器的状态，如果是提供程序包，我只需要在第二个屏幕上使用 Provider.of<counter>(context, listen: false).counter 就可以了显示计数器。

Answer 1

问题是您创建了两次 Provider。您只想创建一次并全局访问它。

从您的 SecondScreen 中删除 final counterProvider = ChangeNotifierProvider<Counter>((ref) => Counter());，而是从您的 FirstScreen 中导入 counterProvider，它会按照您的预期运行。

使用riverpod在flutter中导航到另一个屏幕时如何保留应用程序的状态

1 个答案: