C# delegate
一、委托
當(dāng)我們需要把方法做為參數(shù)傳遞給其他方法的時(shí)候,就需要使用委托。
因?yàn)橛袝r(shí)候,我們要操作的對(duì)象,不是針對(duì)數(shù)據(jù)進(jìn)行的,而是針對(duì)某個(gè)方法進(jìn)行的操作。
?????? 我們還是來以代碼入手
??
Codeusing?System;
namespace?gosoa.com.cn
{
????public?class?test
????{
????????public?delegate?string?GetAString();
????????public?static?void?Main()
????????{
????????????int?x=10;
????????????GetAString?firstString=new?GetAString(x.ToString);
????????????Console.WriteLine(firstString());
????????????//上句和下面這句類似。
????????????//Console.WriteLine(x.ToString());?
????????}
????}
}
?
??? 在上例中,public delegate string GetAString(); 就是聲明了一個(gè)委托(delegate),其語法和方法的定義類似,只是沒有方法體,前面要加上關(guān)鍵字 delegate 。定義一個(gè)委托,基本上是定義一個(gè)新類,所以,可以在任何定義類的地方,定義委托。
注意,在C#中,委托總是自帶一個(gè)有參數(shù)的構(gòu)造函數(shù),這就是為什么在上例中,GetAString firstString=new GetAString(x.ToString); 通過這句初始化一個(gè)新的delegate的時(shí)候,給傳遞了一個(gè)x.ToString 方法。但,在定義delegate的時(shí)候,卻沒有定義參數(shù)。
??????
在看另一個(gè)例子之前,我們先來了解下匿名方法。
?????? 匿名方法的使用,我們看個(gè)例子
?
Codeusing?System;
namespace?gosoa.com.cn
{
????public?class?test
????{
????????delegate?string?GetUrl(string?val);
????????static?void?Main(string?[]?args)
????????{
????????????string?domin="www.gosoa.com.cn";
????????????GetUrl?url=delegate(string??param)
????????????{
?????????????????param="http://"+param;
?????????????????return?param;
????????????};
????????????Console.WriteLine(url(domin));?
????????}
????}
}
?
在本例中,GetUrl url=delegate(string? param) 在這里實(shí)例化一個(gè)delegate的時(shí)候,采用了匿名的方法。本例輸出的結(jié)果是 http://www.gosoa.com.cn
?
接下來我們?cè)倏匆粋€(gè)委托的例子。?
?
Codeusing?System;
namespace?gosoa.com.cn
{
????class?NumberOpthion
????{
????????public?static?double?numOne(double?x)
????????{
????????????return?x*2;
????????}
????????public?static?double?numTwo(double?x)
????????{
????????????return?x*x;
????????}
????}
????public?class?delegateTest
????{
????????
????????delegate?double?DoubleOpration(double?x);
????????static?void?printNumber(DoubleOpration?dp,double?x)
????????{
????????????double?result=dp(x);
????????????Console.WriteLine(
????????????????"value?is?{0},?result?of?DoubleOpration?is?{1}:",x,result????
????????????);
????????}
????????static?void?Main()
????????{
?????????????DoubleOpration?doption?=new?DoubleOpration(NumberOpthion.numOne);????
?????????????printNumber(doption,1.5);
?????????????doption?=new?DoubleOpration(NumberOpthion.?numTwo);????
?????????????printNumber(doption,3.2);
????????}
????}
}
?
首先我們定義了一個(gè)NumberOpthion類。用來對(duì)數(shù)字進(jìn)行*2和2次方運(yùn)算。接著,我們定義了一個(gè)委托delegate double DoubleOpration(double x)。下面,我們定義了printNumber(DoubleOpration dp,double x) 這樣一個(gè)方法,其中一個(gè)參數(shù)就是委托。最后我們DoubleOpration doption =new DoubleOpration(NumberOpthion.numOne);實(shí)例化了一個(gè)委托,并調(diào)用了 printNumber 方法。最后的輸出結(jié)果是
Value is 0.5? result of DoubleOpration is 3;
Value is 3.2? result of DoubleOpration is 10.24;
?
在上例中,我們?nèi)绻捎媚涿椒?#xff0c;代碼就會(huì)如下:?
?
Codeusing?System;
namespace?gosoa.com.cn
{
????public?class?delegateTest
????{
????????delegate?double?DoubleOpration(double?x);
????????static?void?printNumber(DoubleOpration?dp,double?x)
????????{
????????????double?result=dp(x);
????????????Console.WriteLine(
????????????????"value?is?{0},?result?of?DoubleOpration?is?{1}:",x,result????
????????????);
????????}
????????static?void?Main()
????????{
?????????????DoubleOpration?doptionOne?=delegate(double?x){return?x*2;};
?????????????DoubleOpration?doptionTwo?=delegate(double?x){return?x*x;};
?????????????printNumber(doptionOne,1.5);
?????????????printNumber(doptionTwo,3.2);
????????}
????}
}
?
委托,還有一種情況,是多播委托。這個(gè)在以后我們應(yīng)用到的時(shí)候,會(huì)學(xué)習(xí)到。
轉(zhuǎn)載于:https://www.cnblogs.com/Alexander_2009/archive/2009/10/24/1588940.html
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