Csharp Delegate

🎯 What is a Delegate in C#?

A delegate is a type that holds a reference to a method — like a function pointer.

💡 It lets you treat methods like variables — you can pass them around, store them, and call them dynamically.

🧠 Analogy: A Delegate is Like a Remote Control

Imagine a TV remote:

• The remote = delegate

• The TV = method

You don’t care how the TV works — you just press the button, and it does something. You can switch the remote to control different TVs (i.e., assign different methods).

⸻

🧪 Basic Syntax

✅ Step 1: Declare a delegate type

public delegate void SaySomething();

This says: “Any method I use here must return void and take no parameters.” ⸻ ✅ Step 2: Create a method to match

void Hello()
{
	Debug.Log("Hello");
}

⸻

✅ Step 3: Assign the method to the delegate

SaySomething sayHello = Hello;

SaySomething say = Hello; ⸻

✅ Step 4: Call the delegate

sayHello(); //Output: Hello!

⸻

🔧 Built-in Shortcut: Action and Func

C# already includes ready-made delegate types:

Type	Meaning
Action	Delegate with no return value
Action<T>	Delegate with 1 parameter
Func<T>	Delegate that returns a value

🎯 What Is an Event in C#?

An event lets one object notify other objects when something happens — like a button being clicked or a sprite finishing loading. Think of it like this: “Hey, something just happened! Anyone want to respond?"

👶 Beginner Analogy Imagine you’re organizing a party. You say: “When pizza arrives, everyone clap!”

•	“Pizza arrives” = the event
•	“Clap” = the response method (callback)

You’re setting up a rule: when Event A happens, call Method B.

🔧 Basic Syntax

Here’s how to create, subscribe to, and trigger an event.

✅ Step 1: Define a Delegate (function type)

public delegate void MyEventHandler(string message);

This says: “I’ll accept any method that takes a string and returns void.”

✅ Step 2: Declare an Event

public event MyEventHandler OnSomethigHappened;

public event MyEventHandler OnSomethingHappened;

✅ Step 3: Subscribe to the Event

OnSomethingHappend += MyMethod

✅ Step 4: Raise (Trigger) the Event

if (OnSomethingHappened != null)
    OnSomethingHappened("Hello!");

⚡ Modern Shortcut (No Need for Manual Delegate)

In real C# code, we often skip the delegate declaration and use built-in types like Action, Action<T>, or EventHandler.

🔹 Example with Action<string>:

Using UnityEngine;
//...
public event Action<string> OnClick;

void Start()
{
    OnClick += Hear;
    OnClick?.Invoke("Hi!");
}

void Hear(string msg)
{
    Debug.Log("click say" + msg);
}

Summary,

Term	Meaning
event	A signal that something has occured
delegate	A function signature that subscribers must follow
+=	Subscribe a method to run when event triggers