BlocBuilder to discuss

BlocBuilder.dart

import 'package:bloc/bloc.dart';
import 'package:flutter/material.dart';

typedef BlocBuilderCondition<State extends Object> = bool Function(State state);
typedef BlocBuilderConverter<State extends Object, Result extends Object?> = Result Function(State state);
typedef BlocBuilderBuilder<Result extends Object?> = Widget Function(BuildContext context, Result result);

class BlocBuilder<State extends Object, Result extends Object> extends StatelessWidget {
  final bool animate;

  final IStateObservable<State> bloc;
  final BlocBuilderCondition<State>? buildWhen;
  final BlocBuilderConverter<State, Result>? convert;
  final BlocBuilderBuilder<Result> builder;

  final Widget Function(BuildContext context, String error) onError;
  final Widget Function(BuildContext context) onWaiting;

  const BlocBuilder({
    Key? key,
    required this.bloc,
    required this.builder,
    this.buildWhen,
    this.convert,
    required this.onError,
    required this.onWaiting,
    this.animate = true,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final Stream<State> stream = buildWhen == null //
        ? bloc.stream
        : bloc.stream.where((state) => buildWhen!(state));

    final Stream<Result> resultStream = convert == null //
        ? stream.map((state) => state as Result)
        : stream.map((state) => convert!(state));

    final Result? state = convert == null //
        ? (bloc.state is Result ? bloc.state as Result : null)
        : convert!(bloc.state);

    return StreamBuilder(
      initialData: state,
      stream: resultStream.distinct(),
      builder: (context, AsyncSnapshot<Result> snapshot) {
        Widget result;
        if (snapshot.hasError) {
          result = onError(context, snapshot.error);
        } else if (snapshot.hasData) {
          Result data = snapshot.data!;
          result = builder(context, data);
        } else {
          result = onWaiting(context);
        }

        if (animate) return AnimatedSwitcher(duration: const Duration(milliseconds: 500), child: result);
        return result;
      },
    );
  }
}