bloc_provider.dart

import 'package:flutter/material.dart';

abstract class BlocBase {
    void dispose();
}

class BlocProvider<T extends BlocBase> extends StatefulWidget {
      BlocProvider({
        Key key,
        @required this.child,
        @required this.bloc,
      }) : super(key: key);

    final T bloc;
    final Widget child;

    @override
    _BlocProviderState<T> createState() => _BlocProviderState<T>();

    static T of<T extends BlocBase>(BuildContext context) {
        final type = _typeOf<BlocProvider<T>>();
        BlocProvider<T> provider = context.ancestorWidgetOfExactType(type);
        return provider.bloc;
    }

    static Type _typeOf<T>() => T;
}

class _BlocProviderState<T> extends State<BlocProvider<BlocBase>> {
    @override
    void dispose() {
        widget.bloc.dispose();
        super.dispose();
    }

    @override
    Widget build(BuildContext context) {
        return widget.child;
    }
}