Delegates as callback pattern in C Sharp (C#) - Mini Project: Build & Apply

Delegates as callback pattern

📖 Scenario: You are building a simple notification system where a process can notify different actions when it finishes.

🎯 Goal: Create a delegate to act as a callback, assign methods to it, and invoke it to notify when a process is done.

📋 What You'll Learn

Create a delegate type called ProcessCompleted that takes no parameters and returns void

Create a method called NotifyUser that prints "Process completed!"

Create a method called LogCompletion that prints "Logging: Process finished."

Create a delegate variable called callback and assign NotifyUser to it

Add LogCompletion to the callback delegate invocation list

Invoke the callback delegate to run all assigned methods

💡 Why This Matters

🌍 Real World

Delegates are used to implement callbacks, event handling, and flexible method calls in many C# applications like UI programming and asynchronous operations.

💼 Career

Understanding delegates is essential for C# developers to write modular, reusable, and event-driven code in professional software development.

1

Create the delegate type and methods

Create a delegate type called ProcessCompleted that takes no parameters and returns void. Then create two methods: NotifyUser that prints "Process completed!" and LogCompletion that prints "Logging: Process finished."

C Sharp (C#)

// Your code here

Need a hint?

Use public delegate void ProcessCompleted() to declare the delegate. Define two static methods with Console.WriteLine inside.

2

Create the delegate variable and assign the first method

Inside Main, create a variable called callback of type ProcessCompleted and assign it to the method NotifyUser.

C Sharp (C#)

using System;

public delegate void ProcessCompleted();

class Program
{
    public static void NotifyUser()
    {
        Console.WriteLine("Process completed!");
    }

    public static void LogCompletion()
    {
        Console.WriteLine("Logging: Process finished.");
    }

    static void Main()
    {
        // Create delegate variable callback and assign NotifyUser
        // Your code here
    }
}

Need a hint?

Use ProcessCompleted callback = NotifyUser; to assign the method to the delegate variable.

3

Add the second method to the delegate

Add the method LogCompletion to the callback delegate invocation list using the += operator.

C Sharp (C#)

using System;

public delegate void ProcessCompleted();

class Program
{
    public static void NotifyUser()
    {
        Console.WriteLine("Process completed!");
    }

    public static void LogCompletion()
    {
        Console.WriteLine("Logging: Process finished.");
    }

    static void Main()
    {
        ProcessCompleted callback = NotifyUser;
        // Add LogCompletion to callback
        // Your code here
    }
}

Need a hint?

Use callback += LogCompletion; to add the method to the delegate.

4

Invoke the delegate to run all methods

Invoke the callback delegate to run all assigned methods.

C Sharp (C#)

using System;

public delegate void ProcessCompleted();

class Program
{
    public static void NotifyUser()
    {
        Console.WriteLine("Process completed!");
    }

    public static void LogCompletion()
    {
        Console.WriteLine("Logging: Process finished.");
    }

    static void Main()
    {
        ProcessCompleted callback = NotifyUser;
        callback += LogCompletion;
        // Invoke the callback delegate
        // Your code here
    }
}

Need a hint?

Call the delegate like a method: callback();