Building the ActionScript library of a native extension

Build the ActionScript side of your extension into a SWC file. The SWC file is an ActionScript library — an archive file that contains your ActionScript classes and other resources, such as its images and strings.

When you package a native extension, you need both the SWC file and a separate library.swf file, which you extract from the SWC file. The SWC file provides the ActionScript definitions for authoring and compilation. The library.swf provides the ActionScript implementation used by a specific platform. If different target platforms of your extension require different ActionScript implementations, create multiple SWC libraries and extract the library.swf file separately for each platform. A best practice, however, is that all the ActionScript implementations have the same public interfaces. (Only one SWC file can be included in the ANE package.)

The SWC file contains a file called library.swf. For more information, see The SWC file and SWF files in the ANE package .

Use one of the following ways to build the SWC file:

Use Adobe Flash Builder to create a Flex library project.

When you build the Flex library project, Flash Builder creates a SWC file. See Create Flex library projects .

Be sure to select the option to include Adobe AIR libraries when you create your Flex library project.

Ensure that the SWC is compiled to the correct version of the SWF format. Use SWF 11 for AIR 2.7, SWF 13 for AIR 3, SWF 14 for AIR 3.1, and so on. You can set the SWF file format version in the project’s properties. Select ActionScript Compiler and enter this Additional Compiler Argument:
```
-swf-version 17
```
Note: You can use swfdump in the Flex SDK bin directory to check the SWF file format version of any SWF file: swfdump myFlexLibraryProjectSWF.swf
Use the command-line tool acompc to build a Flex library project for AIR. This tool is the component compiler provided with the Flex SDK. If you are not using Flash Builder, use acompc directly. See Using compc, the component compiler .

For example:
```
acompc -source-path $HOME/myExtension/actionScript/src 
                                -include-classes sample.extension.MyExtensionClass sample.extension.MyExtensionHelperClass 
                                -swf-version=13 
                                -output $HOME/myExtension/output/sample.extension.myExtension.swc
```
Note: If your ActionScript library uses any external resources, package them into the ANE file using ADT. See Creating the native extension package .

SWF version compatibility

The SWF version specified when compiling the ActionScript library is one of the factors, along with extension descriptor namespace, that determines whether the extension is compatible with an AIR application. The SWF version of the extension cannot exceed the SWF version of the main application SWF file:

Compatible AIR application version	ANE SWF version	Extension namespace
3.0+	10-13	ns.adobe.com/air/extension/2.5
3.1+	14	ns.adobe.com/air/extension/3.1
3.2+	15	ns.adobe.com/air/extension/3.2
3.3+	16	ns.adobe.com/air/extension/3.3
3.4+	17	ns.adobe.com/air/extension/3.4
3.5+	18	ns.adobe.com/air/extension/3.5
3.6+	19	ns.adobe.com/air/extension/3.6
3.7+	20	ns.adobe.com/air/extension/3.7

Note: The platform options (platform.xml) file requires the ns.adobe.com/air/extension/3.1 namespace or later. If you are using the ‑platformoptions flag to package your ANE, you must specify ns.adobe.com/air/extension/3.1 or later and a SWC version greater than or equal to 14. Some platform options file features require later AIR namespace and SWF versions.