What is Multicast Delegate in C#?

A multicast delegate in C# is a special type of delegate that can hold references to multiple methods. It allows you to combine multiple methods into a single delegate object, and when the delegate is invoked, all the referenced methods are called sequentially. In other words, a multicast delegate can invoke multiple methods in one invocation.

Here are some key points about multicast delegates:

  1. Delegate Invocation:
    • When a multicast delegate is invoked, all the methods it references are invoked in the order they were added.
    • Each method’s return value is ignored except for the last method, whose return value is returned as the overall result.
  2. Syntax:
    • Multicast delegates are created using the + and - operators to combine or remove method references from the delegate.
    • You can use the += operator to add a method to a delegate and the -= operator to remove a method.
    • The delegate must be declared using the delegate keyword and the signature matching the combined method signatures.
  3. Event Handling:
    • Multicast delegates are commonly used in event handling scenarios.
    • Event handlers are added or removed from an event using the += and -= operators, respectively.
    • When an event is raised, all the registered event handlers (methods) are invoked.

Here’s an example to demonstrate the usage of a multicast delegate:

delegate void MyDelegate(string message);

class Program
{
    static void Main()
    {
        MyDelegate myDelegate = Method1;
        myDelegate += Method2;
        myDelegate += Method3;

        myDelegate("Hello, delegates!");

        // Output:
        // Method1: Hello, delegates!
        // Method2: Hello, delegates!
        // Method3: Hello, delegates!
    }

    static void Method1(string message)
    {
        Console.WriteLine("Method1: " + message);
    }

    static void Method2(string message)
    {
        Console.WriteLine("Method2: " + message);
    }

    static void Method3(string message)
    {
        Console.WriteLine("Method3: " + message);
    }
}

In this example, a multicast delegate myDelegate of type MyDelegate is created. Three methods, Method1, Method2, and Method3, are added to the delegate using the += operator. When the delegate is invoked with a message, all three methods are called sequentially, and each method appends a prefix to the message.

The output demonstrates that all three methods are invoked in the order they were added to the delegate.

It’s important to note that not all delegates support multicast. A delegate must be declared with the delegate keyword and have the appropriate signature to support multicast. If a delegate does not support multicast, adding or removing methods will replace the previous reference with the new one.

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