Bits of .NET

📞 Delegates = Function Pointers

Passing methods as parameters? Delegates enable callbacks. Events enable notifications. Essential for event-driven programming.

📝 Delegates

// Declare delegate
public delegate void ProcessDelegate(string message);

// Method matching delegate
public void PrintMessage(string msg) => Console.WriteLine(msg);

// Use delegate
ProcessDelegate handler = PrintMessage;
handler("Hello");

// Multicast delegate
handler += msg => Console.WriteLine($"Another: {msg}");
handler("World"); // Both methods called

// Func and Action (built-in delegates)
Action print = msg => Console.WriteLine(msg);
Func add = (a, b) => a + b;
Func isEven = n => n % 2 == 0;

🎯 Events

public class Button
{
    public event EventHandler Clicked;
    public event EventHandler CustomClick;
    
    public void Click()
    {
        Clicked?.Invoke(this, EventArgs.Empty);
        CustomClick?.Invoke(this, new ButtonEventArgs("Clicked"));
    }
}

public class ButtonEventArgs : EventArgs
{
    public string Message { get; }
    public ButtonEventArgs(string message) => Message = message;
}

// Usage
Button btn = new Button();
btn.Clicked += (sender, e) => Console.WriteLine("Button clicked");
btn.Clicked += (sender, e) => Console.WriteLine("Second handler");
btn.Click();

// Remove event handler
btn.Clicked -= (sender, e) => Console.WriteLine("Second handler");

💡 Use Cases

• UI event handling (click, hover)
• Callback functions (async operations)
• Observer pattern (notifications)
• LINQ (Func delegates)
• Plugins and extensibility