Custom event arguments in C Sharp (C#) - Mini Project: Build & Apply

Custom Event Arguments in C#

📖 Scenario: You are building a simple notification system where a TemperatureSensor reports temperature changes. You want to send extra information about the temperature when it changes.

🎯 Goal: Create a custom event argument class to hold the temperature value, raise an event with this custom argument, and handle the event to display the temperature.

📋 What You'll Learn

Create a class called TemperatureChangedEventArgs that inherits from EventArgs and has a property Temperature of type double.

Create a class called TemperatureSensor with an event TemperatureChanged using EventHandler<TemperatureChangedEventArgs>.

Add a method SetTemperature in TemperatureSensor that raises the TemperatureChanged event with the new temperature.

Create a Main method that creates a TemperatureSensor, subscribes to TemperatureChanged, and prints the temperature when the event is raised.

💡 Why This Matters

🌍 Real World

Custom event arguments are used in real applications to send extra information when something important happens, like sensor updates or user actions.

💼 Career

Understanding custom events is important for building interactive and responsive applications in C# and many other programming environments.

1

Create the custom event argument class

Create a public class called TemperatureChangedEventArgs that inherits from EventArgs. Add a public property Temperature of type double with a getter and a constructor that sets this property.

C Sharp (C#)

# Your code here

Need a hint?

Remember to inherit from EventArgs and create a constructor that sets the Temperature property.

2

Create the TemperatureSensor class with an event

Create a public class called TemperatureSensor. Inside it, declare a public event called TemperatureChanged of type EventHandler<TemperatureChangedEventArgs>. Also, add a private field _temperature of type double.

C Sharp (C#)

using System;

public class TemperatureChangedEventArgs : EventArgs
{
    public double Temperature { get; }

    public TemperatureChangedEventArgs(double temperature)
    {
        Temperature = temperature;
    }
}

// Your code here

Need a hint?

Declare the event using EventHandler<TemperatureChangedEventArgs> and a private field to store temperature.

3

Add SetTemperature method to raise the event

In the TemperatureSensor class, add a public method called SetTemperature that takes a double parameter called temperature. Inside this method, set the private field _temperature to the new value, then raise the TemperatureChanged event if it is not null, passing this and a new TemperatureChangedEventArgs with the new temperature.

C Sharp (C#)

using System;

public class TemperatureChangedEventArgs : EventArgs
{
    public double Temperature { get; }

    public TemperatureChangedEventArgs(double temperature)
    {
        Temperature = temperature;
    }
}

public class TemperatureSensor
{
    private double _temperature;
    public event EventHandler TemperatureChanged;

    // Add SetTemperature method below
    // Your code here
}

Need a hint?

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

4

Subscribe to the event and print the temperature

Add a Main method inside a Program class. Inside Main, create a new TemperatureSensor object called sensor. Subscribe to the TemperatureChanged event with a lambda that takes sender and e and prints "Temperature changed to {e.Temperature}". Then call sensor.SetTemperature(25.5).

C Sharp (C#)

using System;

public class TemperatureChangedEventArgs : EventArgs
{
    public double Temperature { get; }

    public TemperatureChangedEventArgs(double temperature)
    {
        Temperature = temperature;
    }
}

public class TemperatureSensor
{
    private double _temperature;
    public event EventHandler TemperatureChanged;

    public void SetTemperature(double temperature)
    {
        _temperature = temperature;
        TemperatureChanged?.Invoke(this, new TemperatureChangedEventArgs(temperature));
    }
}

// Add Program class with Main method below
// Your code here

Need a hint?

Subscribe to the event using += and a lambda expression. Use Console.WriteLine to print the temperature.