C#中的委托和事件

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;namespace Study_05_Observer设计模式
{// 计数器public class Counter{int x;int y;//声明委托public delegate void CountEventHandler(object sender, CountEventArgs e);public event CountEventHandler Counted;// 为Observer传递感兴趣的参数public class CountEventArgs : EventArgs{public readonly int x;public readonly int y;public CountEventArgs(int x, int y){this.x = x;this.y = y;}}// 调用此函数，就会通知Observer，Observer会执行注册进Counted事件的方法protected virtual void OnCounted(CountEventArgs e){if (Counted != null)Counted(this, e);}public void Count(){for (int m = 0; m < 21; ++m){y = m;for (int n = 0; n < 21; ++n){x = n;CountEventArgs e = new CountEventArgs(x, y);OnCounted(e);}Console.WriteLine();}}}// 绘图器public delegate bool Condition(int x, int y); // 绘图条件public class Drawer{public event Condition condition;public Drawer(Condition condition) { this.condition = condition; }public void DrawType(object sender, EventArgs e){Counter.CountEventArgs args = e as Counter.CountEventArgs;if (condition(args.x,args.y))Console.Write("0");elseConsole.Write(" ");}}class Program{static bool Condition_1(int x, int y){if (Math.Pow(x - 10, 2) + Math.Pow(y - 10, 2) < 80)return false;elsereturn true;}static void Main(string[] args){Drawer drawer = new Drawer(Condition_1);Counter counter = new Counter();counter.Counted += drawer.DrawType;counter.Count();Console.ReadKey();}}
}

本例中Counter差数器遍历x,y坐标，Drawer负责按条件进行绘图。首先初始化Drawer，添加条件。把画图功能注册入查数器查数事件，每次查数时触发画图。