C# 标准事件模式示例

using System;

namespace ConsoleApp3_Test
{

    internal class Aa
    {

        static void Main(string[] args)
        {
            Stock stock = new Stock("THPW"); 
            stock.Price = 27.10M;

            //Register with the PriceChanged event
            stock.PriceChanged += stock_PriceChanged;
            stock.Price = 31.59M;
        }

        static void stock_PriceChanged(object sender, PriceChangedEventArgs e)
        {
            Console.WriteLine($"LastPrice:{e.LastPrice}\t\tNewPrice:{e.NewPrice}");

            if (e.LastPrice != 0 && (e.NewPrice - e.LastPrice) / e.LastPrice > 0.1M)
                Console.WriteLine("Alert, 10% stock price increase!");

            Console.WriteLine();
        }
    }

    public class PriceChangedEventArgs : EventArgs
    {
        public readonly decimal LastPrice;
        public readonly decimal NewPrice;

        public PriceChangedEventArgs(decimal lastPrice, decimal newPrice)
        {
            LastPrice = lastPrice;
            NewPrice = newPrice;
        }
    }

    public class Stock
    {
        string symbol;
        decimal price;
        public Stock(string symbol) { this.symbol = symbol; }

        public event EventHandler<PriceChangedEventArgs> PriceChanged;

        protected virtual void OnPriceChanged(PriceChangedEventArgs e)
        {
            PriceChanged?.Invoke(this, e);
        }

        public decimal Price
        {
            get { return price; }
            set
            {
                if (price == value) return;
                decimal oldPrice = price;
                price = value;
                OnPriceChanged(new PriceChangedEventArgs(oldPrice, price));
            }
        }
    }
}