Raising events safely in C Sharp (C#) - Mini Project: Build & Apply

Raising events safely

📖 Scenario: Imagine you are building a simple notification system where a class sends messages to subscribers when something important happens.

🎯 Goal: You will create a class with an event, set up a subscriber method, and raise the event safely to notify subscribers without errors.

📋 What You'll Learn

Create a delegate type called NotifyEventHandler that takes object sender and EventArgs e parameters

Create a class called Notifier with an event called OnNotify of type NotifyEventHandler

Write a method RaiseNotification in Notifier that raises OnNotify safely using a local copy

Create a subscriber method called HandleNotification that prints a message when notified

Subscribe HandleNotification to the OnNotify event

Call RaiseNotification to trigger the event and display the message

💡 Why This Matters

🌍 Real World

Events are used in user interfaces, messaging systems, and many applications to notify parts of a program when something happens.

💼 Career

Understanding how to raise events safely is important for writing reliable and thread-safe C# applications, a common requirement in software development jobs.

1

Create the delegate and Notifier class with event

Create a delegate called NotifyEventHandler that takes object sender and EventArgs e. Then create a class called Notifier with an event OnNotify of type NotifyEventHandler.

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 the RaiseNotification method with safe event raising

Inside the Notifier class, add a method called RaiseNotification that creates a local copy of OnNotify and invokes it with this and EventArgs.Empty if the copy is not null.

C Sharp (C#)

using System;

public delegate void NotifyEventHandler(object sender, EventArgs e);

public class Notifier
{
    public event NotifyEventHandler OnNotify;

    // Your code here
}

Need a hint?

Copy the event delegate to a local variable to avoid race conditions when raising events.

3

Create a subscriber method and subscribe to the event

Outside the Notifier class, create a method called HandleNotification that takes object sender and EventArgs e and prints "Notification received!". Then create a Notifier object called notifier and subscribe HandleNotification to notifier.OnNotify.

C Sharp (C#)

using System;

public delegate void NotifyEventHandler(object sender, EventArgs e);

public class Notifier
{
    public event NotifyEventHandler OnNotify;

    public void RaiseNotification()
    {
        NotifyEventHandler handler = OnNotify;
        if (handler != null)
        {
            handler(this, EventArgs.Empty);
        }
    }
}

// Your code here

Need a hint?

Subscriber methods must match the delegate signature. Use += to subscribe to events.

4

Call RaiseNotification to trigger the event and print the message

In the Main method, after subscribing HandleNotification to notifier.OnNotify, call notifier.RaiseNotification() to raise the event and display the message.

C Sharp (C#)

using System;

public delegate void NotifyEventHandler(object sender, EventArgs e);

public class Notifier
{
    public event NotifyEventHandler OnNotify;

    public void RaiseNotification()
    {
        NotifyEventHandler handler = OnNotify;
        if (handler != null)
        {
            handler(this, EventArgs.Empty);
        }
    }
}

class Program
{
    static void HandleNotification(object sender, EventArgs e)
    {
        Console.WriteLine("Notification received!");
    }

    static void Main()
    {
        Notifier notifier = new Notifier();
        notifier.OnNotify += HandleNotification;
        // Your code here
    }
}

Need a hint?

Calling the method that raises the event will notify all subscribers and print the message.