delegate vs event

🟢 1. Delegate

• Think of it as: A variable that can store a method.

• Purpose: Let you pass methods around like data.

• Analogy: A remote control that can point to different TVs (methods).

Example

// Define a delegate type (method signature)
public delegate void MyDelegate(string msg);

class Program
{
    static void Print(string m) => Console.WriteLine(m);

    static void Main()
    {
        MyDelegate d = Print;  // store method in delegate
        d("Hello from delegate"); // call it
    }
}

• You can assign, combine, or call (d(...)) a delegate directly.

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🟢 2. Event

• Think of it as: A special wrapper around a delegate used for notifications.

• Purpose: Publisher/Subscriber system — when something happens, tell all listeners.

• Analogy: A doorbell. Many people can listen (subscribe). Only the house owner can ring (raise) it.

Example

using System;

class Door
{
    public event Action DoorOpened; // event based on built-in delegate

    public void Open()
    {
        Console.WriteLine("Door opened");
        DoorOpened?.Invoke(); // only Door can trigger
    }
}

class Program
{
    static void Main()
    {
        var door = new Door();
        door.DoorOpened += () => Console.WriteLine("Guest notified!");
        door.Open();
    }
}

• Others use += or -= to subscribe/unsubscribe.

• Only the class that defines the event can raise (Invoke) it.

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🟢 Key Differences

Feature	Delegate	Event
What is it?	Type-safe reference to a method	A delegate with extra rules for publish/subscribe
Who can call (invoke)?	Anyone holding the delegate	Only the declaring class
Usage	Pass methods as parameters, callbacks	Notify subscribers when something happens
Subscription	Not required; can directly assign	Must use += or -=
Encapsulation	None	Provides safety: outsiders can’t overwrite the list

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🟢 Simple Rule

• Delegate: “Point to a method and call it.”

• Event: “Many listeners can sign up; only the owner can fire it.”

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Tiny Summary

• Delegate = function pointer (method reference).

• Event = delegate used for notifications with extra safety and += / -= subscription.