A SWC file is an archive file, sometimes also referred to as a class library, for Flex components and other assets. SWC files contain a SWF file and a catalog.xml file, in addition to properties files and other uncompiled assets such as CSS files. The SWF file implements the compiled component or group of components and includes embedded resources as symbols. Flex applications extract the SWF file from a SWC file and use the SWF file's contents when the application refers to resources in that SWC file. The catalog.xml file lists of the contents of the component package and its individual components.

In most cases, the symbols defined in the SWF file that are referenced by the application are embedded in the Flex application at compile-time. This is known as static linking. The application compiler only includes those classes that are used by your application, and dependent classes, in the final SWF file.

You can also dynamically link the contents of SWC files. Dynamic linking is when the entire SWF file is loaded at run time. To achieve dynamic linking of the SWF file, you must use the SWC file as a Runtime Shared Library, or RSL. For more information, see Using Runtime Shared Libraries.

SWC files make it easy to exchange components and other assets among Flex developers. You need only exchange a single file, rather than the MXML or ActionScript files and images and other resource files. The SWF file in a SWC file is compiled, which means that the code is loaded efficiently and it is hidden from casual view. Also, compiling a component as a SWC file can make namespace allocation an easier process.

You can package and expand SWC files with tools that support the PKZip archive format, such as WinZip or jar. However, do not manually change the contents of a SWC file, and do not try to run the SWF file that is in a SWC file in Flash Player.

You typically create SWC files by using compc, the command-line component compiler. You can also save SWC files as open directories rather than archived files. This give you easier access to the contents of the SWC file. You create an open directory SWC by setting the directory option to true. This is typically only used when you create an RSL because RSLs require that you deploy the SWF file with your application.

The properties files inside SWC files are uncompiled text files in UTF-8 format. They are used as resource bundles for localization of Flex applications. Within the SWC file, they are stored in the /locale/locale_string directory, where locale_string is something like en_US or fr_FR. For more information, see Localizing Flex Applications in Adobe Flex 3 Developer Guide.

Distributing SWC files

After you generate a SWC file, you can use it in your Flex applications.

You can also copy SWC files to a directory specified by the library-path compiler option. You must store SWC files at the top level of the user_classes directory or the directory specified by the library-path. You cannot store SWC files in subdirectories.

To use a SWC file when compiling components or applications from the command line or from within Flex Builder, you specify the location of the SWC file with the library-path compiler option.

Using components in SWC files

If a component in a SWC file does not have a namespace, you can add a generic namespace identifier in your <mx:Application> tag to use the component, as the following example shows:

<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" xmlns:a="*">

If the component has a package name as part of its namespace, you must do one of the following:

1. Add the package name to the namespace declaration in the <mx:Application> tag; for example:

   <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" xmlns:but="mycomponents.*">
   
   

2. Create a manifest file and recompile the SWC file. You pass the manifest file to the compc compiler by using the namespace option. In the <mx:Application> tag, you specify only the unique namespace URI that you used with compc. For more information on specifying a namespace for the component, see Compiling components using namespaces.