为什么我的应用程序没有在简单的计数器中通过 ProviderListener？

Question

我正在测试 riverpod，但它不起作用。

我只想拥有典型的计数器，当它达到 2 时，它会转到另一个屏幕。计数器工作但不启动第二个屏幕或通过 ProviderListener。

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',
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

final _counterProvider = StateNotifierProvider<CounterStateNotifier>((ref) {
  return CounterStateNotifier();
});

class CounterStateNotifier extends StateNotifier<int> {
  CounterStateNotifier([int count]) : super(count ?? 0);

  void increment() {
    state++;
  }
}

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

  final String title;

  @override
  Widget build(BuildContext context, ScopedReader watch) {
    final int _counter = watch(_counterProvider.state);
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: ProviderListener<StateNotifier<int>>(
        provider: _counterProvider,
        onChange: (context, _counter) {
          if (_counter == 2) {
            Navigator.pushReplacement(
              context,
              MaterialPageRoute(
                builder: (BuildContext context) => ScondScreen(),
              ),
            );
          }
        },
        child: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                'You have pushed the button this many times:',
              ),
              Text(
                '$_counter',
                style: Theme.of(context).textTheme.headline4,
              ),
            ],
          ),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          context.read(_counterProvider).increment();
        },
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

我还没有找到 ProviderListener 示例来指导我。

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Answer 1

因为我个人在尝试帮助发现这个新事物之前并没有使用它。

在这里我可以看到： https://riverpod.dev/docs/concepts/reading#providerlistener

那个代码是

Widget build(BuildContext context) {
  return ProviderListener<StateController<int>>(
    provider: counterProvider,
    onChange: (context, counter) {
      if (counter.state == 5) {
        showDialog(...);
      }
    },
    child: Whatever(),
  );
}

不同之处在于，在示例中有 counter.state == variable，而在您的示例中有 counter == variable，但如果 onChange 甚至没有触发，情况可能就是这样

ProviderListener<StateController<int>>

在你的情况下，它基于 stateNotifier 而不是控制器（我猜它不一样）

ProviderListener<StateNotifier<int>>

Answer 2

已解决更改为 ChangeNotifier:

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,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

final _counterProvider = ChangeNotifierProvider<CounterChangeNotifier>((ref) {
  return CounterChangeNotifier();
});

class CounterChangeNotifier extends ChangeNotifier {
  CounterChangeNotifier([this.count = 0]);

  int count;

  void increment() {
    count++;
    notifyListeners();
  }
}

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

  final String title;

  @override
  Widget build(BuildContext context, ScopedReader watch) {
    final counter = watch(_counterProvider);
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: ProviderListener<CounterChangeNotifier>(
        provider: _counterProvider,
        onChange: (context, counter) {
          if (counter.count == 2) {
            Navigator.push(
              context,
              MaterialPageRoute<ScondScreen>(
                builder: (_) => ScondScreen(),
              ),
            );
          }
        },
        child: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                'You have pushed the button this many times:',
              ),
              Text(
                '${counter.count}',
                style: Theme.of(context).textTheme.headline4,
              ),
            ],
          ),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          context.read(_counterProvider).increment();
          //counter.state++;
        },
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

为什么我的应用程序没有在简单的计数器中通过 ProviderListener？

Why my app does not go through ProviderListener in a simple counter?

flutter

state

counter

state-management

riverpod