O’Reilly: Inside RIA

In LFFS - 9, we included a "homework" assignment in the form of a non-functioning calculator with the hopes that those new to Flex may learn from attempting to get it to work. After I came up with a solution, it was code-reviewed by Adam, and a few changes were made in order to comply with best practices. We've included the source code for both, but we will be focusing our attention on the revised version as we go through an explanation of the code step by step.

In our last installment, we briefly introduced the MXML language. We learned that all MXML tags are used as a sort of "short hand" representation of ActionScript code in Flex applications. This time, we continue to look at MXML and it's role as a helpful tool within the Flex programming environment.

All of the material in this article involving code, and indeed all code examples so far in the series, have been written using Flex Builder 3.0. It's worth noting that although we haven't yet devoted an entire installment to the use of Flex Builder, (we will very soon), those new to Flex and wishing to learn more should definitely head straight to the Adobe product downloads page and grab their free 60 day trial. Flex Builder is as good as it gets as far as I. D. E. s are concerned, and a great way to learn programming is to start messing around with code to try to get things to happen. On that note, we've included a sample application for you to experiment with, but more on that later.

Let's continue our focus on the languages of Flex with a little discussion of MXML. We've learned that rich internet applications by their nature have more advanced functionality than say, a typical web page laid out with just HTML. We've also learned that the way a Flex application achieves this advanced functionality is by using ActionScript to provide the "logic" for its applications. Lucky for developers, there's a way to quickly employ the power of ActionScript to create applications that also have the look and feel of anything web based. Flex developers can use MXML.

In this installment of Learning Flex From Scratch, I'm going to diverge a bit

from the usual content, and devote this time to disclosing the most helpful resources I've found so far on my journey into Flex. There's a lot of information out there for those who want to learn Flex, but nonetheless it can be tricky sometimes to find that perfect resource that answers your questions.

Organizing data into chunks is a fundamental part of our cognitive experience. The ability to understand individual items in terms of their membership within a group saves our brains an immense amount of processing power. Imagine the difficult time you'd have if, when you went to the grocery store, all of the things you needed to pick up were written on separate pieces of paper instead of on a nicely organized list. You could still get your shopping done, but it would be a real pain to shuffle through all those individual sheets! In addition, you'd have to make sure that all of those sheets really actually contained things you needed to pick up from the store, and not perhaps, things that you already had in your refrigerator. In other words, using an organized system that groups items together into meaningful lists saves you a lot of time and effort.

In order for software to be useful, it needs to be able to react to its environment. Put another way, a program needs to have logic. The logic of an application gives it the ability to change course when a given condition is met. Program flow in ActionScript 3.0 is controlled by conditionals and loops. Both conditionals and loops are responsible for determining whether a particular code block is executed, and are therefore placed within a method body. The main difference between the two is that conditionals decide on executing one collection of statements over another, and loops allow a collection of statements to execute over and over. As we'll soon see, loops, like many things in object-oriented programming, are great tools that provide the very important element of scalability. But first, a bit about conditionals.

As promised, the current installment of Learning Flex From Scratch focuses on the syntax of ActionScript 3.0. We know from the previous post that an application written in an object-oriented programming language involves, by definition, the use of objects. Objects, we found out, are derived from classes, which serve as a blueprint for the object's methods and properties. This post goes into the details of creating a class in ActionScript 3.0, providing a foundation for our journey into the language. The code examples provided here are strictly theoretical, and shouldn't be thought of as a working piece of software, but rather as a starting point to illustrate some basic language concepts.

As we have previously mentioned, Flex 3 makes use of ActionScript 3.0, a powerful object-oriented programming language. Before we dive into the specific syntax used in ActionScript, let's take a look at what makes a language object-oriented in the first place, and the benefits to using and object-oriented language versus a procedural language.

In this post we take a deeper look at what Flex is and what it can do. Our goal is to provide a clear picture of the environment in which you use Flex to create Rich Internet Applications (RIAs). Fist, let's have a quick discussion about the nature of RIAs so that we can understand why we would want to use Flex in the first place.

The "Learning Flex From Scratch" series written by Adam Flater and Scott Sheridan, aims to help not only a Flex novice, but also a programming novice jump into the world of creating Rich Internet Applications using Flex. The installments of the series will cover everything from installing the Flex Builder I.D.E., to some background information on object-oriented programming. You'll even get to learn about advanced topics like source control and design patterns (a la Cairngorm) from the perspective of a beginner.