A Widget that subscribes/cancels to a Stream and dispatch the events to the supplied listen function.

stream_listener_widget.dart

/*
MIT License
Copyright (c) 2020 Ronaldo Pace
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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 */

import 'dart:async';

import 'package:flutter/widgets.dart';

/// A widget that subscribes/cancels to a Stream
/// and dispatch the events to the supplied [listen] function.
///
/// Different from StreamBuilder,
/// this widget does not re-built when a stream event happen.
///
/// This is useful for events coming from the block
/// that does not change the UI state of the widget,
///
/// Example, Navigation:
///
/// return StreamListener<String>(
///   child: myUi,
///   stream: bloc.navigation
///   listen: (data) { Navigator.pushNamed(context, data) }
/// );
class StreamListener<T> extends StatefulWidget {
  const StreamListener({
    Key key,
    @required this.child,
    @required this.stream,
    @required this.listen,
  }) : super(key: key);

  final Widget child;
  final Stream<T> stream;
  final void Function(T) listen;

  @override
  State<StatefulWidget> createState() {
    return _StreamListenerState<T>(child, stream, listen);
  }
}

class _StreamListenerState<T> extends State<StreamListener> {
  _StreamListenerState(this._child, this._stream, this._listen);

  Widget _child;
  Stream<T> _stream;
  void Function(T) _listen;
  StreamSubscription<T> _subscription;

  @override
  void initState() {
    _subscribe();
    super.initState();
  }

  void _subscribe() {
    _subscription?.cancel();
    _subscription = _stream.listen(_listen);
  }

  void _dispose() {
    _subscription?.cancel();
    _subscription = null;
  }

  @override
  void didUpdateWidget(StreamListener<T> oldWidget) {
    super.didUpdateWidget(oldWidget);
    _dispose();
    _child = widget.child;
    _stream = widget.stream;
    _listen = widget.listen;
    _subscribe();
  }

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

  @override
  Widget build(BuildContext context) {
    return _child;
  }
}