Chapter 2: Designing with Classes and Tiers

Overview

Some developers resent user interface programming because they believe it's all about painting icons, rewording text, and endlessly tweaking dialog boxes until an entire company agrees that an application looks attractive. Certainly, making a program usable, elegant, and even impressive (or cool) is no trivial task. It can even make the difference between indifferent customers and an enthusiastic audience that's willing to promote your product tirelessly. This kind of excitement about a program's look and feel has driven obscure products like Kai's Power Tools and even Microsoft Windows to great success, and it can't be overlooked. However, developers who are involved in creating and maintaining sophisticated enterprise-level applications realize that there is another set of design considerations for user interface programming. These are considerations about application architecture.

Application architecture determines how a user interface "plugs in" to the rest of an application. Today's development software (like MFC, Visual Basic, and .NET) makes this interaction relatively straightforward and, as a result, developers usually spend little or no time thinking about it. User interface code is usually inserted wherever is most immediately convenient at the time the program is written. This almost always leads to interface code that's tightly bound to a particular problem, scenario, or data source, and heavily interwoven with the rest of the application logic. The interface code might look good on the outside, but it's almost impossible to enhance, reuse, or alter with anything more than trivial changes. To make the jump from this type of scattered user interface coding to a more modern style you have to stop thinking in terms of windows and controls, and start looking at user interface as an entire interrelated framework.

This chapter explains how the principles of object-oriented programming and three-tier architecture apply to user interface design. It identifies the overall concepts that you'll return to again and again throughout the book, including:

How controls and windows use objects.

Why inheritance is more important for user interface design than for business logic.

How the .NET framework approaches user interface design, and how it affects your coding practices.

What makes an interface data-driven and well encapsulated.

What the dream of three-tier design promises, why it's so hard to achieve, and whether other solutions are possible.

The emphasis in this chapter is on general concepts. You'll see some code, but you won't learn about the intricate details like the properties and methods that controls provide. All these details are explored as we delve deeper into controls and user interface coding in the chapters that follow.