事件简单例子

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace EventTest
{
    /// <summary>
    /// 事件订阅者类
    /// </summary>
    class Program
    {
        static void Main(string[] args)
        {
            Counter c = new Counter(new Random().Next(10));
            c.ThresholdReached += c_ThresholdReached;  // 订阅事件（注册事件）

            Console.WriteLine("press 'a' key to increase total");
            while(Console.ReadKey(true).KeyChar=='a')
            {
                Console.WriteLine("adding one");
                c.Add(1);
            }
            Console.ReadLine();
        }

        static void c_ThresholdReached(object sender, CounterEventArgs e) // 事件处理程序
        {
            Console.WriteLine("The threshold was reached And Value is {0}.",e.total);
            //Environment.Exit(0);
        }
    }

    /// <summary>
    /// 事件数据类
    /// </summary>
    public class CounterEventArgs : EventArgs
    {
        public int total;
        public CounterEventArgs(int passedTotal)
        {
            total = passedTotal;
        }
    }

    /// <summary>
    /// 事件发布者类 
    /// </summary>
    /// <remarks>
    /// 功能：实现total值的不断增加。达到阈值时触发事件给出达到阈值的提示。
    /// </remarks>
    public class Counter
    {
        public event EventHandler<CounterEventArgs> ThresholdReached;  // 声明事件

        private int total;
        private int threshold;
        public Counter(int passedThreshold)
        {
            threshold = passedThreshold;
        }

        public void Add(int x)
        {
            total += x;
            if (total >= threshold) // 在每次增加值之后判断是否触发事件
            {
                CounterEventArgs cEArgs = new CounterEventArgs(total);
                OnThresholdReached(cEArgs); // 传递事件数据给事件处理程序
            }
        }

        protected virtual void OnThresholdReached(CounterEventArgs e) // 触发事件
        {
            EventHandler<CounterEventArgs> handler = ThresholdReached;
            if (handler != null)
            {
                handler(this, e);
            }
        }
    }
}