委托,深入浅出才是王道

[来源] 达内    [编辑] 达内   [时间]2012-09-14

委托和事件在 .NET Framework 中的应用非常广泛,较好的理解委托和事件对很多人来说可能并不容易

委托和事件在 .NET Framework 中的应用非常广泛,较好的理解委托和事件对很多人来说可能并不容易。它们像一道坎儿,过了这个坎儿的人,觉得真是太容易了,而没有过去的人每次见到委托和事件就觉得心里模糊,浑身不自在。下面就通过简洁的语言和通俗的例子来讲一下什么是委托、如何实现委托,如何实现委托,以及事件的使用与处理。

< div style="background-color: rgb(245, 245, 245); font-family: 'Courier New'; font-size: 12px; border: 1px solid rgb(204, 204, 204); padding: 5px; overflow: auto; margin: 5px 0px; color: rgb(0, 0, 0); font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; " class="cnblogs_code"> View Code
< p style="margin: 5px auto; text-indent: 0px; color: rgb(0, 0, 0); font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "> 以上代码定义一个pepole类,实现讲中文和英语的方法,通过枚举类型控制说那种语言,这样是很好。但是细想一下,这个方法的扩展性还是太差了,如果以后我们需要再添加法语、德语,就不得不反复修改枚举和SpeakOperate()方法以适应新的需求。

< p style="margin: 5px auto; text-indent: 0px; color: rgb(0, 0, 0); font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; ">那么,有没有更好的解决方案呢?

< p style="margin: 5px auto; text-indent: 0px; color: rgb(0, 0, 0); font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; ">可能你已经想到了,我们可以使用委托。

< h4 style="color: rgb(0, 0, 0); font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; font-style: normal; font-variant: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; ">引入委托 < p style="margin: 5px auto; text-indent: 0px; color: rgb(0, 0, 0); font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; ">我们先来看看SpeakOperate()方法的声明:

< div style="background-color: rgb(245, 245, 245); font-family: 'Courier New'; font-size: 12px; border: 1px solid rgb(204, 204, 204); padding: 5px; overflow: auto; margin: 5px 0px; color: rgb(0, 0, 0); font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; " class="cnblogs_code">
public
 void SpeakOperate(string name, Language lang)
< p style="margin: 5px auto; text-indent: 0px; color: rgb(0, 0, 0); font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "> 可以看到,我们需要传入两个参数,然后根据枚举类型判断用哪个方法进行处理。我们假设SpeakOperate()方法可以接收一个参数变量,这个参数变量可以代表一个方法,我们只需要传入方法名然后执行相应方法,对了,这就是委托!

< p style="margin: 5px auto; text-indent: 0px; color: rgb(0, 0, 0); font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; ">      在C#中,定义委托的语法是:

< div style="background-color: rgb(245, 245, 245); font-family: 'Courier New'; font-size: 12px; border: 1px solid rgb(204, 204, 204); padding: 5px; overflow: auto; margin: 5px 0px; color: rgb(0, 0, 0); font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; " class="cnblogs_code">
delegate
 void SpeakDelegate(string name);
< p style="margin: 5px auto; text-indent: 0px; color: rgb(0, 0, 0); font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; ">delegate关键字用于声明一个引用类型,该类型可用于封装命名方法和匿名方法。

< p style="margin: 5px auto; text-indent: 0px; color: rgb(0, 0, 0); font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; ">下面用委托来改造一下这个demo,只需定义一个委托,然后更改SpeakOperate()方法即可:

< div style="background-color: rgb(245, 245, 245); font-family: 'Courier New'; font-size: 12px; border: 1px solid rgb(204, 204, 204); padding: 5px; overflow: auto; margin: 5px 0px; color: rgb(0, 0, 0); font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; " class="cnblogs_code">
public
 delegate void
 SpeakDelegate(string name); 
public

 void SpeakOperate(string


 name, SpeakDelegate speak_method) {     speak_method(name); }
< p style="margin: 5px auto; text-indent: 0px; color: rgb(0, 0, 0); font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; ">Main函数中的调用如下:

< div style="background-color: rgb(245, 245, 245); font-family: 'Courier New'; font-size: 12px; border: 1px solid rgb(204, 204, 204); padding: 5px; overflow: auto; margin: 5px 0px; color: rgb(0, 0, 0); font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; " class="cnblogs_code">
复制代码
static
 void Main(string


[] args) {     PepoleClass pc = new PepoleClass();     pc.SpeakOperate(
@"张三
", pc.SpeakChinese);     pc.SpeakOperate(
@"

张三"
, pc.SpeakEnglish);     Console.ReadLine(); }
复制代码
< h4 style="color: rgb(0, 0, 0); font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; font-style: normal; font-variant: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; ">总结: < p style="margin: 5px auto; text-indent: 0px; color: rgb(0, 0, 0); font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "> 委托是一种特殊的对象类型,它定义了方法的类型,是的可以将方法当作另一个方法的参数来进行传递,其特殊之处在于,我们以前定义的所有对象都包含数据,而委托包含的只是方法的地址。这种方法动态地赋值给参数的做法,可以避免在程序中大量使用if…else、switch语句,同时使得程序既有更好的扩展性。

< p style="margin: 5px auto; text-indent: 0px; color: rgb(0, 0, 0); font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19px; orphans: 2; text-align: -webkit-auto; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; ">多播委托,请听下回分解

资源下载