Advanced C# Tutorial: Introduction to Delegates and Events

Objective

The next part of our tutorial will introduce you to delegates and events in C#. You will expand the console application created in the previous part to incorporate these concepts, allowing for a deeper understanding of event-driven programming in C#.

Prerequisites

• Completion of the previous part where you set up a basic C# console application.
• Familiarity with basic C# concepts such as classes, methods, and interfaces.

Part 2: Integrating Delegates and Events

Step 1: Introduce Delegates

Delegates are types that represent references to methods with a particular parameter list and return type. They are used to pass methods as arguments to other methods and are especially useful for implementing event handling.

1. Define a Delegate:
   • In your Program class, define a delegate that takes a string as an input and returns void. This delegate will be used to display messages.

csharpCopy codepublic delegate void DisplayMessage(string message);

2. Create a Method that Matches the Delegate Signature:
   • Add a static method in your Program class that conforms to the DisplayMessage delegate.

csharpCopy codestatic void ShowMessage(string message)
{
    Console.WriteLine(message);
}

Step 2: Understanding and Implementing Events

Events in C# are a way to make a class able to notify other classes when something happens. They are based on the delegate model.

1. Define an Event:
   • Add an event of your delegate type in the Program class. This event is triggered when a user enters their name.

csharpCopy codepublic static event DisplayMessage UserLoggedIn;

2. Trigger the Event:
   • Modify the Main method to trigger the event when the user enters their name.

csharpCopy codestatic void Main(string[] args)
{
    Console.WriteLine("Enter your name: ");
    string name = Console.ReadLine();
    UserLoggedIn?.Invoke($"Hello, {name}!");
}

3. Subscribe to the Event:
   • In the Main method, before asking for the user’s name, subscribe the ShowMessage method to the UserLoggedIn event.

csharpCopy codeUserLoggedIn += ShowMessage;

Step 3: Run and Test Your Application

1. Run Your Program:
   • Compile and run your program. Enter your name when prompted and observe that the ShowMessage method is called when the UserLoggedIn event is triggered, displaying the personalized greeting.
2. Understanding the Flow:
   • The program asks for the user’s name.
   • Upon entering the name, the UserLoggedIn event is triggered.
   • The ShowMessage method subscribed to this event is called and executes, displaying the message.

Assignment: Enhancing the Application with Additional Events

Now that you have a basic understanding of delegates and events, your task is to enhance the application by adding additional functionality:

1. Implement a Goodbye Event:
   • Define a new delegate and event for saying goodbye.
   • Trigger this event when the application is about to close.
2. Create Interactive Commands:
   • Allow the user to type commands into the console, such as “exit” to close the application.
   • Use events to handle these commands appropriately.
3. Documentation:
   • Document your code with comments explaining each part of the event and delegate implementation.
4. Test Your Application:
   • Ensure that all events are triggered and handled as expected.

This exercise will solidify your understanding of how delegates and events are used in C# to facilitate communication between different parts of an application. This pattern is particularly useful in designing responsive, user-interactive applications.