委托(1)

委托本质上是一种类型跟int、float、string一样，int、float、string可以作为参数传递，声明了委托之后方法也可以像int、float、string一样作为参数传递。

委托一般以EventHandler结尾。

委托的简单使用

public delegate string SayHiEventHandler(string name);
public class DelegateHelper
{
public void SimpleDelegate()
{
//完整形式
SayHiEventHandler sayHi = new SayHiEventHandler(SayHiByChinese);
//隐式调用委托
string result = sayHi("蝈蝈");
Console.WriteLine("result=" + result);
sayHi = new SayHiEventHandler(SayHiByEnglish);
//显示调用委托sayHi.Invoke("guoguo");等价于sayHi("guoguo");
result = sayHi.Invoke("guoguo");
Console.WriteLine("result=" + result);

//简写形式
SayHiEventHandler sayHiSimple = SayHiByChinese;
result = sayHiSimple("蝈蝈");
Console.WriteLine("result=" + result);
sayHiSimple = SayHiByEnglish;
result = sayHiSimple.Invoke("guoguo");
Console.WriteLine("result=" + result);
}

public string SayHiByEnglish(string name)
{
Console.WriteLine("Hello：" + name);
return "success";
}
public string SayHiByChinese(string name)
{
Console.WriteLine("你好：" + name);
return "成功";
}
}

运行结果如下：

委托链

委托只能操作与之定义的返回值类型、参数类型、个数都一样的方法。

public delegate string SayHiEventHandler(string name);
public class DelegateHelper
{
public void DelegateLink()
{
SayHiEventHandler sayHi = SayHiByChinese;
sayHi += SayHiByEnglish;
//此时调用委托链sayHi("蝈蝈")相当于连续执行SayHiByChinese("蝈蝈");SayHiByEnglish("蝈蝈");
string result = sayHi("蝈蝈");
//result是最后一个方法SayHiByEnglish方法的返回值
Console.WriteLine("result=" + result);
Console.WriteLine("---------------");
//委托链能加也能减
sayHi -= SayHiByEnglish;
result = sayHi("蝈蝈");
//result是SayHiByChinese方法的返回值
Console.WriteLine("result=" + result);
Console.WriteLine("---------------");
}
}

运行结果如下：

传递委托类型参数

当方法需要委托类型的参数时，传递过去的方法的返回值类型、参数个数、类型必须与委托完全一致。

//Program.cs文件代码
class Program
{
static void Main(string[] args)
{
new DelegateHelper().SayHi("蝈蝈",new DelegateHelper().SayHiByChinese);
new DelegateHelper().SayHi("guoguo", new DelegateHelper().SayHiByEnglish);
Console.ReadKey();
}
}
//DelegateHelper.cs文件代码
public delegate string SayHiEventHandler(string name);
public class DelegateHelper
{
public void SayHi(string name,SayHiEventHandler sayHi)
{
sayHi(name);
}
}

运行结果如下：