stream memory caching example for flutter/dart

readme.md

swift-jungle-8148

Created with <3 with dartpad.dev.

main.dart

import 'dart:async';
import 'dart:math';

/// {@template cache_client}
/// An in-memory cache client.
/// {@endtemplate}
class CacheClient {
  /// {@macro cache_client}
  CacheClient() : _cache = <String, Object>{};

  final Map<String, Object> _cache;

  final _cacheUpdatesController =
      StreamController<Map<String, Object>>.broadcast();

  /// Stream of cache updates, emitted whenever the cache is modified.
  Stream<Map<String, Object>> get cacheUpdates =>
      _cacheUpdatesController.stream;

  /// Writes the provide [key], [value] pair to the in-memory cache.
  void write<T extends Object>({required String key, required T value}) {
    if (_cache[key] != value) {
      _cacheUpdatesController.add(_cache); // Emit a cache update event
    }
    _cache[key] = value;
  }

  /// Looks up the value for the provided [key].
  /// Defaults to `null` if no value exists for the provided key.
  T? read<T extends Object>({required String key}) {
    final value = _cache[key];
    if (value is T) return value;
    return null;
  }

  /// dispose the internal stream controller
  void dispose() {
    _cacheUpdatesController.close();
  }
}

class Account {
  const Account({required this.id, this.name});

  final String id;
  final int? name;

  static const empty = Account(id: '');
}

class AuthRepository {
  AuthRepository() {
    Stream<int> watchCounter() async* {
      while (true) {
        await Future.delayed(const Duration(seconds: 1));
        yield Random().nextInt(10000);
      }
    }

    watchCounter().listen(
      (event) => _cache.write(
        key: userCacheKey,
        value: Account(id: '1', name: event),
      ),
    );
  }

  final CacheClient _cache = CacheClient();

  static const userCacheKey = '__user_cache_key__';

  Stream<Account> get user {
    return _cache.cacheUpdates
        .where((cache) => cache.containsKey(userCacheKey))
        .map((cache) => cache[userCacheKey] as Account? ?? Account.empty);
  }

  void updateCache() {
    _cache.write(
        key: userCacheKey,
        value: Account(id: '1', name: Random().nextInt(1000)));
  }
}

void main() {
  final authRepo = AuthRepository();

  authRepo.user.listen((event) => print(event.name));

  for (var i = 0; i < 10; i++) {
    Future.delayed(Duration(seconds: i), () => authRepo.updateCache());
  }
}