Why events are needed in C Sharp (C#) - See It in Action

Why events are needed

📖 Scenario: Imagine you are building a simple alarm clock app. When the alarm time comes, you want the app to notify the user by showing a message. But you want the app to be flexible so that later you can add other actions like playing a sound or sending a message without changing the alarm clock code.

🎯 Goal: You will create a simple program that uses an event to notify when the alarm time is reached. This shows why events are useful: they let different parts of a program communicate without being tightly connected.

📋 What You'll Learn

Create a class called AlarmClock with an event called AlarmRang

Create a method called SetAlarm that triggers the AlarmRang event

Create a method called OnAlarmRang that handles the event and prints a message

Use the event to notify when the alarm time is reached

💡 Why This Matters

🌍 Real World

Events are used in apps to notify when something important happens, like a button click or a timer finishing.

💼 Career

Understanding events is key for building interactive applications and working with user interfaces or asynchronous programming.

1

Create the AlarmClock class with an event

Create a class called AlarmClock with a public event called AlarmRang of type EventHandler.

C Sharp (C#)

public class AlarmClock
{
    // Your code here
}

Need a hint?

Use public event EventHandler AlarmRang; inside the class.

2

Add SetAlarm method to trigger the event

Add a public method called SetAlarm inside the AlarmClock class that triggers the AlarmRang event by calling it with this and EventArgs.Empty.

C Sharp (C#)

using System;

public class AlarmClock
{
    public event EventHandler AlarmRang;

    // Your code here
}

Need a hint?

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

3

Create OnAlarmRang method to handle the event

Create a public method called OnAlarmRang that takes object sender and EventArgs e parameters and prints "Alarm rang! Time to wake up!".

C Sharp (C#)

using System;

public class AlarmClock
{
    public event EventHandler AlarmRang;

    public void SetAlarm()
    {
        AlarmRang?.Invoke(this, EventArgs.Empty);
    }

    // Your code here
}

Need a hint?

This method matches the event handler signature and prints the message.

4

Subscribe to the event and trigger the alarm

In the Main method, create an AlarmClock object called alarm. Subscribe the OnAlarmRang method to the AlarmRang event. Then call alarm.SetAlarm() to trigger the event and print the message.

C Sharp (C#)

using System;

public class AlarmClock
{
    public event EventHandler AlarmRang;

    public void SetAlarm()
    {
        AlarmRang?.Invoke(this, EventArgs.Empty);
    }

    public void OnAlarmRang(object sender, EventArgs e)
    {
        Console.WriteLine("Alarm rang! Time to wake up!");
    }
}

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

Need a hint?

Subscribe to the event using alarm.AlarmRang += alarm.OnAlarmRang; and then call alarm.SetAlarm();.