合并委托（多路广播委托）

合并委托（多路广播委托）

本示例演示如何创建多播委托。
委托对象的一个有用属性是：可以使用 + 运算符将多个对象分配给一个委托实例。
多播委托包含已分配委托的列表。
在调用多播委托时，它会按顺序调用列表中的委托。
只能合并相同类型的委托。
- 运算符可用于从多播委托中移除组件委托。

C#
using System;

// Define a custom delegate that has a string parameter and returns void.
delegate void CustomDel(string s);

class TestClass
{
// Define two methods that have the same signature as CustomDel.
static void Hello(string s)
{
System.Console.WriteLine("  Hello, {0}!", s);
}

static void Goodbye(string s)
{
System.Console.WriteLine("  Goodbye, {0}!", s);
}

static void Main()
{
// Declare instances of the custom delegate.
CustomDel hiDel, byeDel, multiDel, multiMinusHiDel;

// In this example, you can omit the custom delegate if you
// want to and use Action<string> instead.
//Action<string> hiDel, byeDel, multiDel, multiMinusHiDel;

// Create the delegate object hiDel that references the
// method Hello.
hiDel = Hello;

// Create the delegate object byeDel that references the
// method Goodbye.
byeDel = Goodbye;

// The two delegates, hiDel and byeDel, are combined to
// form multiDel.
multiDel = hiDel + byeDel;

// Remove hiDel from the multicast delegate, leaving byeDel,
// which calls only the method Goodbye.
multiMinusHiDel = multiDel - hiDel;

Console.WriteLine("Invoking delegate hiDel:");
hiDel("A");
Console.WriteLine("Invoking delegate byeDel:");
byeDel("B");
Console.WriteLine("Invoking delegate multiDel:");
multiDel("C");
Console.WriteLine("Invoking delegate multiMinusHiDel:");
multiMinusHiDel("D");
}
}
/* Output:
Invoking delegate hiDel:
Hello, A!
Invoking delegate byeDel:
Goodbye, B!
Invoking delegate multiDel:
Hello, C!
Goodbye, C!
Invoking delegate multiMinusHiDel:
Goodbye, D!
*/