By Ryan Vice
Separation of Concerns or SoC is a core principle of enterprise software development which provides many benefits and has been a key driving force behind many presentation (or UI) design patterns that have emerged over the last 30 years. In the arena of Silverlight and WPF development, Model View View Model or MVVM has quickly become the de-facto pattern for achieving SoC in UIs. However, this pattern often leaves developers and architects frustrated and at the time of this writing, can be difficult to implement in an effective way that provides more benefits than some of the older, more familiar presentation patterns (MVC, MVP, and so on).
In this chapter we will cover the evolution of presentational patterns along with the problems that are solved by each pattern along the evolutionary path. We will also dive into the shortcomings of each pattern which led to the next pattern in the evolution and will finish this chapter ready to look at MVVM.
We will begin this chapter by reviewing the functionality of the Project Billing sample application that we will use throughout this book. We will follow this by briefly talking about the various types of state that must be managed in UI applications. Then we dive into the history of presentational patterns and as we go through the history we will implement Project Billing using each pattern to show you explicitly the benefits and the shortcomings of each pattern that lead to the next pattern in the evolution. This will help you understand why you'd want to use MVVM through examples and make the benefits of MVVM easier to appreciate when we dive into that topic in the next chapter. This would also help you evangelize the pattern on your projects if needed and be able to explain what benefits MVVM would offer over other presentation patterns.
If you are already familiar with (or not interested in) the history of presentation patterns, you should still at a minimum review the following sections:
The Project Billing sample application: This section will review the functionality of the sample application that will be used in the first two chapters
Types of state: This section defines and discusses the various types of state that need to be managed in a UI application
Monolithic design: The introduction of this section discusses the coupling that results from not using some kind of presentational design pattern
The problems with Monolithic design: This section discusses the many problems that result from not using presentational design patterns
Data service stub: This section covers creating the data service stub that will be used by the Project Billing application throughout this book
Memory leaks: This section covers how .NET events can cause memory leaks
However, I'd recommend that unless you are intimately familiar with patterns such as Model 2 and Passive View that you take the time to go through this chapter as this knowledge will be very useful in driving home some of the fundamentals of presentation patterns which will help you adapt these notoriously flexible patterns to your needs