HOW TO：組合委派 (多點傳送委派) (C# 程式設計手冊)

本範例示範如何建立多點傳送委派。delegate 物件具有的一種有用屬性，就是可使用 + 運算子將多個物件指派給一個委派執行個體。多點傳送委派包含已指派委派的清單。呼叫多點傳送委派時，它會依順序叫用清單中的委派。只有相同型別的委派才能加以結合。

- 運算子可用來從多點傳送委派中移除某個元件委派。

範例

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)
    {
        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!
*/

請參閱

參考

事件 (C# 程式設計手冊)

MulticastDelegate

概念

C# 程式設計手冊