Flex is a highly productive, free open source framework for building and maintaining expressive web applications that deploy consistently on all major browsers, desktops, and operating systems. While Flex applications can be built using only the free Flex SDK, developers can use Adobe® Flex® Builder™ 3 software to dramatically accelerate development.

1. Flex frameworks

2. The Frameworks The Cairngorm framework MATE PureMVC The Swiz framework Robotlegs Spring ActionScript Parsley

3. Cairngorm Framework Cairngorm is the oldest and best known of the Flex frameworks. It is actually a micro-architecture—that is, a collection of design patterns that have proven to work well with one another. Cairngorm borrows heavily from the world of Java development and focuses on three key areas: handling user actions, encapsulating server interactions and business logic, and managing the state on the client and representing that state in the user interface (UI). Building a project in Cairngorm involves breaking your application into several packages and extending the Cairngorm classes.

4. Cairngorm Framework Strengths Cairngorm is well known in the Flex community and, as a project on Adobe's Open Source site, is well supported and has an active community of developers who continue to work on it. Also, it borrows proven strategies from the Java development world and has been successfully used to create many large-scale projects. Finally, it is well suited for team development, because it provides a highly structured methodology for creating applications that allow distribution of tasks. Weaknesses Perhaps the most common criticism leveled against Cairngorm is that it requires you to write a lot of classes. In Cairngorm, each event maps to a command; therefore, you have to write a command class for every event your program can trigger. Additionally, you must write any other classes that the command must use, such as delegates. This can quickly turn into a large number of classes for even a modest-sized application. Second, because Cairngorm implements its own method of handling events, it can complicate the built-in Flex event model. It also has some limitations. Because each event must have its own command class, you are limited to one responder per event. Also, Cairngorm events do not bubble, so if you want to notify things higher up the container hierarchy, you will have to do that yourself. A third common criticism is the framework's reliance on global singletons, which can make modularization and unit testing difficult. Although you can break up the model among several singletons to make these processes easier, the extra work required can complicate the process.

5. MATE Framework Mate is a tag-based, event-driven framework. Tag based means that it is implemented entirely in MXML. It is event driven in that the central focus of the framework is to make it easier to define who responds to events. There are only two basic requirements for creating a project using Mate: You must have one or more events, and you must have an MXML file called an event map—that is, a simple MXML file included in the main application file. It defines the events you want to listen to and how they should be handled. You must have at least one of these files, but you can use multiple event maps, if necessary. Mate also implements the idea of dependency injection—sometimes referred to as the Hollywood principle, or "don't call us, we'll call you." Objects are constructed in such a way that the data they require is provided to them or injected into the class. In other words, the classes don't call out to get data ("don't call us") but rather are passed the data they need ("we'll call you").

6. MATE Framework Strengths Mate promotes loose coupling through its use of dependency injection. Because components do not rely on global singletons, they are freer to acts as independent agents. Mate does not keep you from using Flex's built-in event model, nor does it limit you to a single response for each event as Cairngorm does. Mate's MXML files and tags are straightforward and easy to use, and if you get stuck, the documentation is good and there are plenty of code examples on the site. Weaknesses Mate is MXML only. So, if you are one of those developers who like doing everything in Adobe ActionScript classes, you're going to have to adjust your normal routine. Because Mate does not define much of a structure for your application, it's left up to you to define. Hence, you will have to do your own team coordination to ensure that all your developers are coding in a compatible manner.

7. PureMVC Although it is used for Flex, PureMVC was not actually designed as a Flex framework. The creator of PureMVC wanted the framework to be language agnostic. In fact, if you visit the site, you will see that there are implementations and code examples for a variety of languages. PureMVC centers on the Model-View-Controller (MVC) pattern, with the stated goal of separating a project into model, view, and controller tiers. These tiers are represented by three singleton classes—Model, View, and Controller—with a fourth singleton called the Façade that is designed to facilitate communication among the tiers and act as a central repository for accessing their public methods. Much like Cairngorm, creating a project using PureMVC involves dividing your project into several packages, then implementing your classes by extending the framework classes. PureMVC has the addition of the Façade class, which acts as the main entry point for the application.

8. PureMVC Strengths Like Cairngorm, PureMVC is a well-established framework and has a large and active community supporting it. It is also well suited to team development, because it provides a well-defined structure for how applications need to be created, standardizing coding across developers. Weaknesses Because it relies on singletons, PureMVC is prone to many of the same criticisms leveled at Cairngorm. It is not specifically a Flex framework, so it does not take advantage of the features of MXML. Like Cairngorm, PureMVC has its own method of handling events, and it can make working with the standard Flex event model more difficult. PureMVC is a fairly complex framework and has a relatively steep initial learning curve. Unless your team is familiar with it, training new employees can increase production time.

9. The Swiz Framework Swiz is an inversion of control (IoC) framework that provides methodologies for simplifying event handling and asynchronous remote method calls. The main focus of the Swiz framework is to provide a true MVC paradigm in a simple, effective manner. Unlike Cairngorm and PureMVC, it specifically steers clear of imposing Java patterns and does not impose any predefined folder structure.

10. The Swiz Framework Strengths Swiz is simple to use and does not impose a predefined structure onto your project. Through its Autowire dependency-injection system, it—like Mate—promotes loose coupling between components and manages dependencies for you. Also like Mate, Swiz uses built-in Flex event handling while providing help in such key areas as facilitating global event dispatching through the use of an internally referenced singleton. Weaknesses Again, like Mate, Swiz does not define much of a structure for your application—that's left up to you to define. Hence, you will have to do your own team coordination to ensure that all your developers are coding in a compatible manner.

11. RobotLegs

12. Spring ActionScript

13. Parsley (by SpiceLib) http://www.spicefactory.org/parsley/index.php