C#•16mo ago

❔ What of use is the keyword "event"

The essence of the event field is just an object of delegate type which will invoke embedded methods when it is invoked like a method, coding below is also ok:

c#
using System;

class A
{
    public delegate void F(int x, int y);
    static public /*Event*/ F Event;

    public static void Hi()
    {
        Event(1, 2);
    }
}

class B
{
    internal void Print(int x,int y)
    {
        Console.WriteLine(x + y);
    }
}

public class Test
{
    static void Main()
    {
        B suck = new B();
        A.Event += suck.Print;
        A.F x = new A.F(suck.Print);
        A.Hi();
        x(1, 2);
    }
}

c#
using System;

class A
{
    public delegate void F(int x, int y);
    static public /*Event*/ F Event;

    public static void Hi()
    {
        Event(1, 2);
    }
}

class B
{
    internal void Print(int x,int y)
    {
        Console.WriteLine(x + y);
    }
}

public class Test
{
    static void Main()
    {
        B suck = new B();
        A.Event += suck.Print;
        A.F x = new A.F(suck.Print);
        A.Hi();
        x(1, 2);
    }
}

So the question comes.

7 Replies

Kouhai•16mo ago

Is your question why use events instead of just using delegates?

thirteenbinary•16mo ago

Yeah

Kouhai•16mo ago

An event limits who can call the delegates. Basically only the publisher can call/raise the event

public class Foo {
    public static event Action MyEvent;
    public void M() {
        MyEvent();
    }
}

public class Bar {
    public void N() {
        Foo.MyEvent();
    }
}

public class Foo {
    public static event Action MyEvent;
    public void M() {
        MyEvent();
    }
}

public class Bar {
    public void N() {
        Foo.MyEvent();
    }
}

This won't compile Because Bar can only subscribe to the event, it can't raise it Other limits are you can only subscribe/unsubscribe from outside the publisher, you can't really set MyEvent to null for example Yes you can set it to null in the publisher

thirteenbinary•16mo ago

So the difference between the delegate object and the event object is whether it can be raised outside the type.

Kouhai•16mo ago

Yes, events are like a special delegates that can't be raised nor set outside of the type/derived type.

thirteenbinary•16mo ago

Thank u

Accord•16mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ What of use is the keyword "event"