River_pod: The build method of ConsumerWidget is called 2 times

[giandifra]

Describe the bug
The build method of CounterText widget is called 2 times.

To Reproduce

class CounterText extends ConsumerWidget {
  @override
  Widget build(BuildContext context,
      T Function<T>(ProviderBase<Object, T> provider) watch) {
    final count = watch(counterState).state;
    print('update');
    return Text(count.toString());
  }
}

final counterState = StateProvider<int>((ref) => 0});

Expected behavior
The build method of CounterText widget should be called one time at start! (or I may not have understood something about how it works)

Thanks @rrousselGit for another great package

[iamarnas]

@giandifra Hi. I would say you not have understood. It rebuild once on state changes from up to down.

class CounterText extends ConsumerWidget {
  @override
  Widget build(BuildContext context, ScopedReader watch) {
    final count = watch(counterState).state;
    print('update'); // <= print once on rebuild.
    return Center(child: Text('$count')); // <= rebuild once at same time.
  }
}
 ```
`ConsumerWidget` is very useful and good alternative instead `StatefulWidget`. But if you provide multi providers to your `Widget` then I would recommend `Consumer` for better performance and put it deep as possible in your `Widget` tree.

```dart 
//  StatelessWidget....
// Here, rebuilds once only on first run to check the state.
return Scaffold(
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          // This rebuilds only when firstCounterState changes
          Consumer(builder: (context, watch, child) {
            final count = watch(firstCounterState).state;
            print('rebuilding firstCounterState');
            return Center(child: Text('$count'));
          }),
          // This rebuilds only when secondCounterState changes
          Consumer(builder: (context, watch, child) {
            final count = watch(secondCounterState).state;
            print('rebuilding secondCounterState');
            return Center(child: Text('$count'));
          }),
        ],
      ),
    );
//....

final firstCounterState = StateProvider<int>((ref) => 0);
final secondCounterState = StateProvider<int>((ref) => 0);

[giandifra]

@iamarnas I know this. I try to be more clear. This is full example.
Why print(update) is called 2 times at start?

void main() => runApp(ProviderScope(child: MyApp()));

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: CounterText(),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          context.read(counterState).state++;
        },
      ),
    );
  }
}

final counterState = StateProvider<int>((ref) => 0);

class CounterText extends ConsumerWidget {
  @override
  Widget build(BuildContext context,
      T Function<T>(ProviderBase<Object, T> provider) watch) {
    final count = watch(counterState).state;
    print('update');
    return Text(count.toString());
  }
}

[iamarnas]

@giandifra Strange. For me only once.

[giandifra]

The first print(update); is called instantly, the second after 1 second more or less.

[tbm98]

https://github.com/flutter/flutter/issues/52536#issuecomment-599127314

Flutter does not guarantee Widget.build will be called the minimum number of times possible. You should structure your application in a way that assumes build will be called on every frame - anything less is an optimization.

[rrousselGit]

@giandifra Could you share your flutter version, the platform you are using and the steps to reproduce?

I cannot reproduce this issue.

[giandifra]

Flutter 1.20.4 • channel stable • https://github.com/flutter/flutter.git
Framework • revision fba99f6cf9 (13 days ago) • 2020-09-14 15:32:52 -0700
Engine • revision d1bc06f032
Tools • Dart 2.9.2

[rrousselGit]

What about the platform? Android? Web?

[giandifra]

Ops, sorry... I tried on Android Emulator (Android 9) and Pixel 2XL (Android 10)... I saw just now that this behavior only occurs with "Hot Restart" and not in the first launch.

[rrousselGit]

I've tested using the information you gave and still cannot reproduce the issue

But in any case, if this is happening only on hot-restart, it doesn't matter really matter. So I'll close this for now