public static void ShowSimpleObserver() { var investor = new CrazyCryptoInvestor(); var eth = new ETH(new CurrencyInfo { CurrentValue = 2200, ChangeDateTime = DateTime.Now }); eth.Attach(investor); var btc = new BTC(new CurrencyInfo { CurrentValue = 5200, ChangeDateTime = DateTime.Now }); btc.Attach(investor); eth.CurrentValue = new CurrencyInfo { CurrentValue = 2500, ChangeDateTime = DateTime.Now }; }