Professional C# and .NET, 2021st Edition

7Delegates, Lambdas, and Events

WHAT'S IN THIS CHAPTER?

• Delegates
• Lambda expressions
• Closures
• Events

CODE DOWNLOADS FOR THIS CHAPTER

The source code for this chapter is available on the book page at www.wiley.com. Click the Downloads link. The code can also be found at https://github.com/ProfessionalCSharp/ProfessionalCSharp2021 in the directory 1_CS/Delegates.

The code for this chapter is divided into the following major examples:

• SimpleDelegates
• MulticastDelegates
• LambdaExpressions
• EventsSample

All the projects have nullable reference types enabled.

REFERENCING METHODS

Delegates are the .NET variant of addresses to methods. A delegate is an object-oriented type-safe pointer to one or multiple methods. Lambda expressions are directly related to delegates. When the parameter is a delegate type, you can use a lambda expression to implement a method that's referenced from the delegate.

This chapter explains the basics of delegates and lambda expressions, and it shows you how to implement methods called by delegates with lambda expressions. It also demonstrates how .NET uses delegates as the means of implementing events.

NOTE C# 9 also has the concept of a function pointer—a direct pointer to a managed or native method without the overhead of a delegate. Function pointers are explained in Chapter 13, “Managed and Unmanaged Memory.”

DELEGATES

In Chapter 4, “Object-Oriented Programming in C#,” you read about using interfaces as contracts. If the parameter ...