c# - Simple Delegate(委托(delegate))与多播委托(delegate)

Question

我看了很多文章，但我仍然不清楚我们通常创建的普通委托(delegate)和多播委托(delegate)之间的区别。

public delegate void MyMethodHandler(object sender);
MyMethodHandler handler = new MyMethodHandler(Method1);
handler += Method2;
handler(someObject);

上面的委托(delegate) MyMethodHandler 将调用这两个方法。现在多播委托(delegate)从哪里来。我读过他们可以调用多个方法，但恐怕我对委托(delegate)的基本理解是不正确的。

Answer 1

.NET 中的委托(delegate)是多播委托(delegate)。无论您选择将零个还是一个或多个处理程序附加到它们，它们仍然是多播委托(delegate)。

This article解释得很好:

delegate void Del(string s);

class TestClass
{
    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()
    {
        Del a, b, c, d;

        // Create the delegate object a that references 
        // the method Hello:
        a = Hello;

        // Create the delegate object b that references 
        // the method Goodbye:
        b = Goodbye;

        // The two delegates, a and b, are composed to form c: 
        c = a + b;

        // Remove a from the composed delegate, leaving d, 
        // which calls only the method Goodbye:
        d = c - a;

        System.Console.WriteLine("Invoking delegate a:");
        a("A");
        System.Console.WriteLine("Invoking delegate b:");
        b("B");
        System.Console.WriteLine("Invoking delegate c:");
        c("C");
        System.Console.WriteLine("Invoking delegate d:");
        d("D");
    }
}
/* Output:
Invoking delegate a:
  Hello, A!
Invoking delegate b:
  Goodbye, B!
Invoking delegate c:
  Hello, C!
  Goodbye, C!
Invoking delegate d:
  Goodbye, D!
*/