All 17 Delegates, Events & Lambdas questions
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How do you write and use a lambda expression as a shorthand for a delegate? What is a delegate in C#, and how does it enable passing methods as values? What is a closure and what is a common pitfall? How do events differ from plain delegates? What are multicast delegates, and in what order do their subscribed methods get invoked? How does variable capture (closures) work in a C# lambda expression, and what pitfall occurs when capturing a loop variable? What causes event-handler memory leaks and how do you prevent them? What is the difference between multicast delegate invocation and exception handling? How do the built-in Func<>, Action<>, and Predicate<T> generic delegate types differ, and when would you use each? How would you implement the 'weak event pattern' to prevent event subscribers from causing a memory leak by keeping the publisher alive indefinitely?
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What is an event, and how does it differ from a plain public delegate field?

Intermediate

Answer

An event wraps a delegate but RESTRICTS external code to only += (subscribe) and -= (unsubscribe) — external code can't directly invoke the event or overwrite its entire subscriber list with '=', which a plain public delegate field would allow, protecting the publishing class's control over when the event actually fires.
public class Button {
  public event EventHandler? Clicked; // safe: outside code can only += or -=
  public void SimulateClick() => Clicked?.Invoke(this, EventArgs.Empty);
}

var button = new Button();
button.Clicked += (sender, e) => Console.WriteLine("Clicked!");
// button.Clicked = null; // Error: can't do this from outside the class
Real-world example Implementing a UI button's Click event, or a domain model's OnOrderPlaced event that other parts of the system subscribe to.

Common follow-ups: Why is the null-conditional operator (?.Invoke) commonly used when raising an event?

Interfaces & Abstract Classes
All 17 Delegates, Events & Lambdas questions