Custom Stream Builder for Flutter BLoCs

custom_stream_builder.dart

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

class CustomStreamBuilder<State> extends StatelessWidget {
  final Stream stream;
  final Widget errorWidget;
  final Widget initialWidget;
  final Widget Function(BuildContext context, State state) builder;

  CustomStreamBuilder({@required this.stream, @required this.builder, this.errorWidget, this.initialWidget});

  @override
  Widget build(BuildContext context) {
    return StreamBuilder<State>(
      stream: stream,
      builder: (context, AsyncSnapshot<State> snapshot) {
        if (snapshot.hasError) {
          return errorWidget != null ? errorWidget : _buildErrorWidget(context);
        }
        if (!snapshot.hasData) {
          return initialWidget != null ? initialWidget : _buildBlankWidget(context);
        }
        return builder(context, snapshot.data);
      },
    );
  }

  Widget _buildErrorWidget(context) {
    return Container();
  }

  Widget _buildBlankWidget(context) {
    return Container();
  }
}

screen.dart

class Screen extends StatefulWidget {
  final AppBarBloc appBarBloc;

  Screen({@required this.appBarBloc});

  @override
  _ScreenState createState() => _ScreenState();
}

class _ScreenState extends State<Screen> {
  AppBarBloc _appBarBloc;

  @override
  Widget build(BuildContext context) {
    return CustomStreamBuilder<AppBarState>(
      stream: _appBarBloc.appBarTitleStream,
      builder: (context, AppBarState state) {
        return (state is AppBarTitleLoaded) ? Text(state.title) : Container();
      },
    );
  }

  @override
  void dispose() {
    _appBarBloc.dispose();
    super.dispose();
  }
}