Publisher-subscriber execution model in C Sharp (C#) - Mini Project: Build & Apply

Publisher-Subscriber Execution Model in C#

📖 Scenario: Imagine you are building a simple notification system where different parts of a program can listen for messages and react when something important happens.

🎯 Goal: You will create a basic publisher-subscriber model in C#. The publisher will send messages, and subscribers will receive and display those messages.

📋 What You'll Learn

Create a delegate type for the event

Create a publisher class with an event

Create subscriber classes with methods to handle the event

Subscribe the subscriber methods to the publisher's event

Trigger the event to notify all subscribers

Print the messages received by subscribers

💡 Why This Matters

🌍 Real World

Publisher-subscriber models are used in chat apps, notification systems, and event-driven programming to let parts of a program talk to each other easily.

💼 Career

Understanding events and delegates in C# is essential for building responsive applications and working with frameworks like .NET that use event-driven designs.

1

Create a delegate and a publisher class with an event

Create a delegate called MessageHandler that takes a string parameter. Then create a class called Publisher with an event called MessageSent of type MessageHandler.

C Sharp (C#)

// Your code here

Need a hint?

Delegates define the shape of methods that can be called. Events use delegates to notify subscribers.

2

Add a method in Publisher to send messages

In the Publisher class, add a method called SendMessage that takes a string parameter called message. Inside this method, invoke the MessageSent event with the message if it is not null.

C Sharp (C#)

public delegate void MessageHandler(string message);

public class Publisher
{
    public event MessageHandler MessageSent;

    // Your code here
}

Need a hint?

Check if the event has subscribers before calling it to avoid errors.

3

Create subscriber classes with methods to handle messages

Create two classes called SubscriberA and SubscriberB. Each class should have a method called OnMessageReceived that takes a string parameter called message and prints "Subscriber A received: {message}" or "Subscriber B received: {message}" respectively.

C Sharp (C#)

public delegate void MessageHandler(string message);

public class Publisher
{
    public event MessageHandler MessageSent;

    public void SendMessage(string message)
    {
        if (MessageSent != null)
        {
            MessageSent(message);
        }
    }
}

// Your code here

Need a hint?

Use System.Console.WriteLine with string interpolation to print messages.

4

Subscribe methods and send a message

In the Main method, create instances of Publisher, SubscriberA, and SubscriberB. Subscribe SubscriberA.OnMessageReceived and SubscriberB.OnMessageReceived to the Publisher.MessageSent event. Then call SendMessage on the publisher with the message "Hello Subscribers!". Print the output.

C Sharp (C#)

public delegate void MessageHandler(string message);

public class Publisher
{
    public event MessageHandler MessageSent;

    public void SendMessage(string message)
    {
        if (MessageSent != null)
        {
            MessageSent(message);
        }
    }
}

public class SubscriberA
{
    public void OnMessageReceived(string message)
    {
        System.Console.WriteLine($"Subscriber A received: {message}");
    }
}

public class SubscriberB
{
    public void OnMessageReceived(string message)
    {
        System.Console.WriteLine($"Subscriber B received: {message}");
    }
}

class Program
{
    static void Main()
    {
        // Your code here
    }
}

Need a hint?

Use the += operator to subscribe methods to events.