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Flex 4 Cookbook by Garth Braithwaite, Joshua Noble, Todd Anderson, Marco Casario, Rich Tretola

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Chapter 17. Modules and Runtime Shared Libraries

When building Rich Internet Applications, eventually you will have to consider file sizes and download times. The Flex Framework offers several alternatives for separating application code into separate SWF files to enrich the user experience.

Runtime shared libraries (RSLs) are files that can be downloaded and cached on a client. A downloaded RSL persists on the client, and multiple applications can access assets from that cached RSL. Applications can load two types of RSLs: unsigned and signed. Unsigned RSLs, such as standard and cross-domain SWF files, are stored in the browser cache. Signed RSLs, which are libraries that have been signed by Adobe and have the .swz extension, are stored within the Flash Player cache.

As the name suggests, a RSL is loaded at runtime and is considered a dynamically linked library. Statically linked libraries are SWC files that you compile into an application using the library-path and include-libraries compiler options. Application SWF files compiled against statically linked libraries generally have a larger file size and take longer to download, but they have the benefit of running quickly because all the code is available to the application. Applications employing RSLs load faster and have a smaller initial file size, but they may take more time at startup while loading the RSLs and use more memory as a consequence (the entire library of a RSL is loaded by an application without consideration of ...

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