C#——如何合并委托（多播委托）-蒲公英云

C#——如何合并委托（多播委托）

此示例演示如何创建多播委托。委托对象的一个有用属性在于可通过使用 + 运算符将多个对象分配到一个委托实例。多播委托包含已分配委托列表。此多播委托被调用时会依次调用列表中的委托。仅可合并类型相同的委托。

-运算符可用于从多播委托中删除组件委托。

示例

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)
    {
        Console.WriteLine($"  Hello, {s}!");
    }
    static void Goodbye(string s)
    {
        Console.WriteLine($"  Goodbye, {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!
*/