About native extensions

Adobe® AIR® is a cross-operating system runtime that allows content developers to build rich Internet applications (RIAs). The developers can deploy the RIAs to the desktop, mobile devices, and digital home devices. AIR applications can be built using Adobe® Flex® and Adobe® Flash® (SWF-based) and also with HTML, JavaScript, and Ajax (HTML-based). For more information about the Adobe Flash Platform tools that you can use to build AIR applications, see Adobe Flash Platform tools for AIR development in Building Adobe AIR Applications .

SWF-based AIR applications can use Adobe ActionScript® 3.0. ActionScript 3.0 is an object-oriented language that can add interactivity and data-handling to RIAs. For more information about the language, see Learning ActionScript 3.0 and ActionScript 3.0 Developer's Guide .

ActionScript provides many built-in classes. For example, MovieClip, Array, and NetConnection are built-in ActionScript classes. Additionally, a content developer can create application-specific classes. Sometimes an application-specific class derives from a built-in class.

The runtime executes the code in ActionScript classes. The runtime also executes JavaScript code that is used in HTML-based applications.

A native extension is a combination of:

• ActionScript classes.

• Native code. Native code is defined here as code that executes outside the runtime. For example, code that you write in C is native code. On some platforms, Java code is supported in extensions. For the purpose of this documentation, this is also considered “native” code.

Reasons to write a native extension include the following:

• A native code implementation provides access to device-specific features. These device-specific features are not available in the built-in ActionScript classes, and are not possible to implement in application-specific ActionScript classes. The native code implementation can provide such functionality because it has access to device-specific hardware and software.

• A native code implementation can sometimes be faster than an implementation that uses only ActionScript.

• A native code implementation allows you to reuse existing code.

For example, you could create a native extension that allows an application to do the following:

When you have finished your ActionScript and native implementations, you package your extension. Then, an AIR application developer can use the package to call your extension’s ActionScript APIs to execute device-specific functionality. The extension runs in the same process as the AIR application.

ActionScript 3.0 provides a NativeProcess class. This class lets an AIR application execute native processes on the host operating system. This capability is similar to native extensions, which provide access to device-specific features and libraries. When deciding on using the NativeProcess class versus creating a native extension, consider the following:

• Only the extendedDesktop AIR profile supports the NativeProcess class. Therefore, for applications with the AIR profiles mobileDevice and extendedMobileDevice , native extensions are the only choice.

• Native extension developers often provide native implementations for various platforms, but the ActionScript API they provide is typically the same across platforms. When using the NativeProcess class, ActionScript code to start the native process can vary among the different platforms.

• The NativeProcess class starts a separate process, whereas a native extension runs in the same process as the AIR application. Therefore, if you are concerned about code crashing, using the NativeProcess class is safer. However, the separate process means that you possibly have interprocess communication handling to implement.

The most important difference between a native extension and a SWC file is that the SWC file contains no native code. Therefore, if you determine that you can accomplish your goal without native code, use a SWC file rather than a native extension.

You can create native extensions for the following devices:

An extension can target multiple platforms. For more information, see Targeting multiple platforms .

The following AIR profiles support native extensions: