StateBuilder to discuss

StateBuilder.dart

typedef StateBuilderCondition<State extends Object> = bool Function(State state);
typedef StateBuilderConverter<State extends Object, Result extends Object?> = Result Function(State state);
typedef StateBuilderBuilder<Result extends Object?> = Widget Function(BuildContext context, Result result);

typedef StateBuilderOnWaiting = Widget Function(BuildContext context);
typedef StateBuilderOnError = Widget Function(BuildContext context, Object? error);

class StateBuilder {
  @factory
  static _StateBuilder<State> where<State extends Object>({
    Key? key,
    State? initialData,
    required IStateObservable bloc,
    StateBuilderCondition<State>? buildWhen,
    required StateBuilderBuilder<State> builder,
    StateBuilderOnWaiting? onWaiting,
    StateBuilderOnError? onError,
    bool animate = true,
  }) =>
      _StateBuilder<State>(
        key: key,
        initialData: initialData,
        bloc: bloc.whereState<State>(),
        buildWhen: buildWhen,
        builder: builder,
        onError: onError,
        onWaiting: onWaiting,
        animate: animate,
      );

  @factory
  static _StateBuilderConvert<State, Result> whereConvert<State extends Object, Result extends Object?>({
    Key? key,
    Result? initialData,
    required IStateObservable bloc,
    StateBuilderCondition<State>? buildWhen,
    required StateBuilderConverter<State, Result> convert,
    required StateBuilderBuilder<Result> builder,
    StateBuilderOnWaiting? onWaiting,
    StateBuilderOnError? onError,
    bool animate = true,
  }) =>
      _StateBuilderConvert<State, Result>(
        key: key,
        initialData: initialData,
        bloc: bloc.whereState<State>(),
        buildWhen: buildWhen,
        convert: convert,
        builder: builder,
        onError: onError,
        onWaiting: onWaiting,
        animate: animate,
      );
}

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

  final Result? initialData;
  final StateObservable<State> bloc;
  final StateBuilderCondition<State>? buildWhen;
  final StateBuilderConverter<State, Result> convert;
  final StateBuilderBuilder<Result> builder;

  final StateBuilderOnWaiting? onWaiting;
  final StateBuilderOnError? onError;

  const _StateBuilderConvert({
    Key? key,
    this.initialData,
    required this.bloc,
    required this.builder,
    this.buildWhen,
    required this.convert,
    this.onWaiting,
    this.onError,
    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));

    return StreamBuilder(
      initialData: bloc.state is State ? convert(bloc.state) : initialData,
      stream: stream.map(convert).distinct(),
      builder: (context, AsyncSnapshot<Result> snapshot) {
        Widget result;
        if (snapshot.hasError) {
          result = onError != null //
              ? onError!(context, snapshot.error)
              : (context.tryRead<DefaultBlocErrorWidget>() ?? const SizedBox.shrink());
        } else if (snapshot.hasData) {
          final Result data = snapshot.data as Result;
          result = builder(context, data);
        } else {
          result = onWaiting != null //
              ? onWaiting!(context)
              : (context.tryRead<DefaultBlocWaitingWidget>() ?? const SizedBox.shrink());
        }

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

class _StateBuilder<State extends Object> extends StatelessWidget {
  final bool animate;

  final State? initialData;
  final StateObservable<State> bloc;
  final StateBuilderCondition<State>? buildWhen;
  final StateBuilderBuilder<State> builder;

  final StateBuilderOnWaiting? onWaiting;
  final StateBuilderOnError? onError;

  const _StateBuilder({
    Key? key,
    this.initialData,
    required this.bloc,
    required this.builder,
    this.buildWhen,
    this.onWaiting,
    this.onError,
    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));

    return StreamBuilder(
      initialData: bloc.state is State ? bloc.state : initialData,
      stream: stream.distinct(),
      builder: (context, AsyncSnapshot<State> snapshot) {
        Widget result;
        if (snapshot.hasError) {
          result = onError != null //
              ? onError!(context, snapshot.error)
              : (context.tryRead<DefaultBlocErrorWidget>() ?? const SizedBox.shrink());
        } else if (snapshot.hasData) {
          final State data = snapshot.data as State;
          result = builder(context, data);
        } else {
          result = onWaiting != null //
              ? onWaiting!(context)
              : (context.tryRead<DefaultBlocWaitingWidget>() ?? const SizedBox.shrink());
        }

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