EventHandler delegate pattern in C Sharp (C#) - Mini Project: Build & Apply

EventHandler Delegate Pattern

📖 Scenario: Imagine you are building a simple notification system for a doorbell. When someone presses the doorbell, the system should notify the user by printing a message.

🎯 Goal: You will create a program that uses the EventHandler delegate pattern to notify when the doorbell is pressed.

📋 What You'll Learn

Create a class called Doorbell with an event using EventHandler

Create a method called Press in Doorbell that triggers the event

Create a subscriber method called OnDoorbellPressed that handles the event

Subscribe the OnDoorbellPressed method to the doorbell event

Trigger the event by calling Press and print the notification message

💡 Why This Matters

🌍 Real World

EventHandler delegate pattern is used in many applications to notify when something happens, like button clicks, sensor alerts, or data changes.

💼 Career

Understanding events and delegates is essential for C# developers working on desktop apps, web apps, or any interactive software.

1

Create the Doorbell class with an event

Create a class called Doorbell with a public event called Pressed of type EventHandler.

C Sharp (C#)

// Your code here

Need a hint?

Use public event EventHandler Pressed; inside the Doorbell class.

2

Add the Press method to trigger the event

Inside the Doorbell class, add a public method called Press that triggers the Pressed event safely using Pressed?.Invoke(this, EventArgs.Empty);.

C Sharp (C#)

using System;

public class Doorbell
{
    public event EventHandler Pressed;

    // Your code here
}

Need a hint?

Use the null-conditional operator ?. to safely invoke the event.

3

Create the subscriber method and subscribe to the event

Outside the Doorbell class, create a static method called OnDoorbellPressed that matches the EventHandler signature and prints "Doorbell was pressed!". Then, create a Main method where you create a Doorbell object, subscribe OnDoorbellPressed to the Pressed event.

C Sharp (C#)

using System;

public class Doorbell
{
    public event EventHandler Pressed;

    public void Press()
    {
        Pressed?.Invoke(this, EventArgs.Empty);
    }
}

// Your code here

Need a hint?

The subscriber method must match EventHandler signature: void MethodName(object sender, EventArgs e).

4

Trigger the event and print the notification

In the Main method, after subscribing, call the Press method on the doorbell object to trigger the event and print the message.

C Sharp (C#)

using System;

public class Doorbell
{
    public event EventHandler Pressed;

    public void Press()
    {
        Pressed?.Invoke(this, EventArgs.Empty);
    }
}

public class Program
{
    public static void OnDoorbellPressed(object sender, EventArgs e)
    {
        Console.WriteLine("Doorbell was pressed!");
    }

    public static void Main()
    {
        Doorbell doorbell = new Doorbell();
        doorbell.Pressed += OnDoorbellPressed;
        // Your code here
    }
}

Need a hint?

Call doorbell.Press(); to trigger the event and see the message.