Macromedia flex 2 Manual

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Compiling components with Flex 2 SDK
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For example, you can create a component for use by a single application. In that case, you 
store it in the directory structure of the application, usually in a subdirectory under the 
directory that contains the main file of the application. The component is then compiled with 
the entire application into the resultant SWF file.
You can also create a component that is shared among multiple applications as an MXML or 
ActionScript file. In that case, store the component in a location that is included in the 
ActionScript classpath of the application. When Flex compiles the application, it also 
compiles the components included in the application’s ActionScript classpath.
You specify the directory location of the shared components by using one of the following 
methods:
Flex Builder
Open the Project Properties dialog box, and then select Flex Build Path to set 
the ActionScript classpath. 
Command-line compiler
Use the 
source-path
 option to the mxmlc compiler to specify 
the directory location of your shared MXML and ActionScript files. 
Distributing components as SWC files
A SWC file is an archive file of Flex components. SWC files make it easy to exchange 
components among Flex developers. You need to exchange only a single file, rather than the 
MXML or ActionScript files, images, and other resource files. In addition, the SWF file inside 
a SWC file is compiled, which means that the code is hidden from casual view. Finally, 
compiling a component as a SWC file can make namespace allocation an easier process.
SWC files can contain one or more components and are packaged and expanded with the 
PKZIP archive format. You can open and examine a SWC file by using WinZip, JAR, or 
another archiving tool. 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 outside of the SWC file.
When you compile your application, you specify the directory location of the SWC files by 
using one of the following methods:
Flex Builder
Open the Project Properties dialog box, and then select Flex Build Path to set 
the library directories that contain the SWC files. 
Command-line compiler
Set the 
library-classpath
 option to the mxmlc compiler to 
specify the directory location of your SWC files. 
For more information about SWC files, see Chapter 9, “Using the Flex Compilers,” in Building and Deploying Flex 2 Applications, and Chapter 10, “Building Projects,” in Using Flex 
Builder 2