StatefulRebuilder

main.dart

import 'package:flutter/material.dart';

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

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

class MyHomePage extends StatefulWidget {
  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: MyChild(),
      floatingActionButton: FloatingActionButton(
        onPressed: () => setState(() {}),
        child: Icon(Icons.refresh),
      ),
    );
  }
}

class MyChild extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return StatefulRebuilder<int>(
      initState: (context) => 10,
      builder: (context, state, setState) {
        return Center(
          child: RaisedButton(
            child: Text('${state.value}'),
            onPressed: () => setState(() => state.value++),
          ),
        );
      },
    );
  }
}

class StatefulRebuilder<T> extends StatefulWidget {
  final T Function(BuildContext) initState;
  final Widget Function(
    BuildContext,
    StateWrapper<T> state,
    StateSetter setState,
  ) builder;

  StatefulRebuilder({
    Key key,
    @required this.initState,
    @required this.builder,
  }) : super(key: key);

  @override
  State<StatefulRebuilder<T>> createState() => _StatefulBuilderState<T>();
}

class _StatefulBuilderState<T> extends State<StatefulRebuilder<T>> {
  StateWrapper<T> _state;

  @override
  void initState() {
    super.initState();
    _state = StateWrapper(widget.initState(context));
  }

  @override
  Widget build(BuildContext context) {
    return widget.builder(context, _state, setState);
  }
}

class StateWrapper<T> {
  T value;

  StateWrapper(this.value);
}