Introduction

In the previous chapter, you learned some of the key aspects of Object Oriented Programming (OOP). In this chapter, you will build on this by looking at the common patterns used specifically in C# that enable classes to interact.

Have you found yourself working with a code that has to listen to certain signals and act on them, but you cannot be sure until runtime what those actions should be? Maybe you have a block of code that you need to reuse or pass to other methods for them to call when they are ready. Or, you may want to filter a list of objects, but need to base how you would do that on a combination of user preferences. Much of this can be achieved using interfaces, but it is often more efficient to create chunks of code that you can then pass to other classes in a type-safe way. Such blocks are referred to as delegates and form the backbone of many .NET libraries, allowing methods or pieces of code to be passed as parameters.

The natural extension to a delegate...