C# — Events

Basic event

public class Button
{
    public event EventHandler Clicked;

    public void Click()
    {
        Clicked?.Invoke(this, EventArgs.Empty);
    }
}

var button = new Button();
button.Clicked += (sender, e) => Console.WriteLine("Clicked!");
button.Click();

Custom event args

public class OrderEventArgs : EventArgs
{
    public decimal Amount { get; set; }
    public string Product { get; set; }
}

public class OrderService
{
    public event EventHandler<OrderEventArgs> OrderPlaced;

    public void PlaceOrder(string product, decimal amount)
    {
        OrderPlaced?.Invoke(this, new OrderEventArgs
        {
            Product = product,
            Amount = amount
        });
    }
}

Mini Practice

Write C# code that:

1. Creates a basic event
2. Subscribes to an event with +=
3. Uses custom EventArgs
4. Demonstrates event invocation

Up Next

In the next lesson, you'll learn about Attributes — metadata annotations.