日期：2008-6-11
學習內容：委託
遺留問題：今天的內容比較模糊，需要進一步理解
學習總結：
1. 委託
知識點一：委託聲明定義了一種類型，它用一組特定的參數以及返回類型來封裝方法。對於靜態方法，委託對象封裝要調用的方法。對於實例方法，委託對象同時封裝一個實例和該實例的一個方法。如果您有一個委託對象和一組適當的參數，則可以用這些參數調用該委託。
知識點二：委託本質是一個類（可以通過查看IL代碼證實），他是C++中函數指針的替代品；C++中函數的指針只能指向靜態的方法，而在C#中也能指向實例對象。
使用委託的代碼實例：
using System;
delegate void eatMydelegate(string food);
class Mydelegate
{
static void zsEat(string food)
{
Console.WriteLine("張三吃"+food);
}
static void lsEat(string food)
{
Console.WriteLine("李四吃"+food);
}
static void wwEat(string food)
{
Console.WriteLine("王五吃"+food);
}
static void Main ()
{
eatMydelegate zs=new eatMydelegate(zsEat);
eatMydelegate ls=new eatMydelegate(lsEat);
eatMydelegate ww=new eatMydelegate(wwEat);
zs("西瓜");
ls("西瓜");
ww("西瓜");
}
}
上述代碼中三個委託調用同一個參數（西瓜），過於繁瑣有沒有什麼解決辦法呢？委託鏈的引入
using System;
delegate void eatMydelegate(string food);
class Mydelegate
{
static void zsEat(string food)
{
Console.WriteLine("張三吃"+food);
}
static void lsEat(string food)
{
Console.WriteLine("李四吃"+food);
}
static void wwEat(string food)
{
Console.WriteLine("王五吃"+food);
}
static void Main ()
{
eatMydelegate zs=new eatMydelegate(zsEat);
eatMydelegate ls=new eatMydelegate(lsEat);
eatMydelegate ww=new eatMydelegate(wwEat);
eatMydelegate eatChain;//定義委託連
Console.WriteLine("張三，李四，王五，開座談會");
eatChain = zs + ls + ww;
eatChain("西瓜");//給委託鏈賦參數
Console.WriteLine("李四出去接電話");
eatChain -= ls;//c#重載了+=和-=運算符，因此可以創建可變的委託鏈
eatChain("香蕉");
Console.WriteLine("李四回來了");
eatChain += ls;
eatChain("橘子");
}
}
用.net framework2.0引入的新特性，匿名方法，來簡化上面的代碼
using System;
delegate void eatMydelegate(string food);
class Mydelegate
{
static void Main ()
{
eatMydelegate eatChain;
eatChain = null;
eatChain += delegate(string food) { Console.WriteLine("張三吃" + food); };//.net framework2.0引入的新特性
eatChain += delegate(string food) { Console.WriteLine("李四吃" + food); };
eatChain += delegate(string food) { Console.WriteLine("王五吃" + food); };
eatChain("香蕉");
}
}
動態方法代理：
using System;
delegate void eatMydelegate(string food);
class Man
{
private string name;
public Man(string name)
{
this.name = name;
}
public void eat(string food)
{
Console.WriteLine(name + "吃" + food);
}
}
class Party
{
static void eatTogerther(string food, params eatMydelegate[] values)
{
if (values == null)
{
Console.WriteLine("座談會結束");
}
else
{
eatMydelegate eatChain = null;
foreach (eatMydelegate ed in values)
eatChain += ed;
eatChain(food);
Console.WriteLine();
}
}
static void Main ()
{
Man ZS = new Man("張三");
Man LS = new Man("李四");
Man WW = new Man("王五");
eatMydelegate zs = new eatMydelegate(ZS.eat);
eatMydelegate ls = new eatMydelegate(LS.eat);
eatMydelegate ww = new eatMydelegate(WW.eat);
Console.WriteLine("張三，李四，王五，開座談會");
eatTogerther("西瓜",zs,ls,ww);
Console.WriteLine("李四出去接電話");
eatTogerther("香蕉",zs,ww);
Console.WriteLine("李四回來了");
eatTogerther("橘子",zs,ls,ww);
eatTogerther(null,null);
}
}