Delegates

Let’s go over delegates in C# — a fundamental concept for type-safe function references.

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📌 1. What is a Delegate?

• A delegate is a type that represents references to methods with a specific signature.

• In other words, it’s like a pointer to a function that is type-safe.

• Delegates allow methods to be passed as parameters or assigned to variables.

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📌 2. Why Use Delegates?

• Callback methods → pass a method to another method to be called later

• Event handling → events in C# use delegates internally

• Decoupling → allows objects to interact without knowing each other directly

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📌 3. Basic Syntax

// Step 1: Declare a delegate
public delegate void MyDelegate(string message);
 
// Step 2: Define methods matching the delegate signature
public class Program
{
    public static void ShowMessage(string msg)
    {
        Console.WriteLine(msg);
    }
 
    static void Main()
    {
        // Step 3: Instantiate delegate and assign method
        MyDelegate del = ShowMessage;
 
        // Step 4: Call method via delegate
        del("Hello from delegate!");
    }
}

Output:

Hello from delegate!

• MyDelegate can reference any method with void return type and a single string parameter`.

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📌 4. Multicast Delegates

• A delegate can reference multiple methods.

• Use + or += to combine, -= to remove.

public static void AnotherMessage(string msg)
{
    Console.WriteLine("Another: " + msg);
}
 
MyDelegate del = ShowMessage;
del += AnotherMessage;
 
del("Hello again!");

Output:

Hello again!
Another: Hello again!

• Both methods are called in order.

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📌 5. Built-in Delegates

1. Action → method with no return value

   Action<string> action = ShowMessage;
   action("Hi!");

2. Func → method that returns a value

   Func<int, int, int> add = (x, y) => x + y;
   Console.WriteLine(add(3,4)); // 7

3. Predicate → method returning a bool

   Predicate<int> isEven = x => x % 2 == 0;
   Console.WriteLine(isEven(4)); // True

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📌 6. Difference Between Delegate and Event

• Delegate → can be invoked anywhere you have access to it

• Event → can only be invoked inside the class that declared it

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📌 7. Analogy

• Delegate → like a remote control: you assign a method (device) to the delegate (remote), then pressing the remote calls the device.

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✅ Tip:

• Delegates are at the heart of events, callbacks, and functional programming patterns in C#.

• Modern C# often uses Action, Func, lambdas, but understanding delegates is crucial for events.

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