委托和事件：C#

Question

I've got a question on events and delegates in C#. I saw in many codes that they've used the event and delegate keyword to create an event trigger. Let's skip that for now, what concerned me a lot was the functions that the event triggered or rather the functions that were invoked here is the scope snippet.

public delegate void EventHandler();
class Program
{
    //Note : Assigning the evet to the delegate
    public static event EventHandler _show;

    static void Main(string[] args)
    {
        _show += new EventHandler(Dog);
        _show += new EventHandler(Cat);
        _show.Invoke();                   
    }

    static void Dog() {
        Console.WriteLine("Doggie");
    }

    static void Cat(){
        Console.WriteLine("Pussy");
    }

}

`

As you can see there are several functions called Dog / Cat. There return types are void but when you execute it looks like a string value is returned to the event _show . Can someone explain whats going on here?

Answer 1

You are interpreting the syntax wrongly.

static void Main(string[] args)
    {
        _show += new EventHandler(Dog);
        _show += new EventHandler(Cat);
        _show.Invoke();                   
    }

The _show += new EventHandler(Dog) will just queue the function call of Dog() . So its like holding all the function calls in a queue and then executing them in FIFO order.

You are not returning anything here. Only all of your functions are getting called sequentially and then values are getting printed.

Answer 2

The show Event just run the Dog and then run Cat Methods. Obviously, it will print "Doggie" and "Pussy".

If you want to return a string:

static string Dog() {
       // Console.WriteLine("Doggie");
       return "Doggie";
}

and change the delegate decalre:

public delegate string EventHandler();