Mac OS X Hello World native extension example

This example provides a simple native extension for Mac OS X systems. The extension provides the following functionality by using ActionScript code only or by calling native code from ActionScript code:

• Returns a "Hello World" string.
• Reverses the characters of a string.
• Computes the nth prime number, and the time to compute it.
• Inverts an array of numbers, and computes the time to do the inversion.

The attached MacOS-NativeExtension-Test.zip file contains a file called instructions.txt that contains instructions for:

• Installing the AIR runtime, the AIR 3 SDK, and the Flex 4.5.1 SDK.
• Executing shell scripts that build the native extension and the AIR application that uses it.

The source code for the ActionScript library is in the following directory in the ZIP file:

The ActionScript library contains two classes:

• class Basic
• class Advanced

The Basic class

The Basic class provides the public method helloWorld(). The parameter mode indicates whether to:

• use the ActionScript code to provide the "Hello World" string
• call a native function to provide the "Hello World" string

The Advanced class

The Advanced class provides the remaining functionality of the extension. Each of the following public methods takes a parameter mode that indicates whether to use only the ActionScript code, or to call the native code.

• reverseString()
• computeNthPrime()
• timeLongOp() which inverts an array of numbers from 1 to n. The Advanced class constructor takes one parameter, which is the size of the array. This method returns a string showing the elapsed time for the operation.

The Advanced class also provides these public methods:

• getElapsedTime() which computes the elapsed time for computing the nth prime number.
• getUnsorted() which returns a string of the first few elements of the original array that timeLongOp() inverts.
• getSorted() which returns a string of the first few elements of the inverted array.

Extension context types

This extension illustrates using two extension context types:

"Basic"

"Advanced"

Each context type provides a different set of native functions. Multiple extension context types are useful when an extension provides more than one set of capabilities.

The Mac OS X native extension framework is implemented in C, using the native extension C API. The Xcode project and source file for creating the native side are in the following directory in the ZIP file:

Some implementation details to note are:

• The functions NativeExtensionsInitializer() and NativeExtensionsFinalizer() use the FREInitializer() and FREFinalizer() signatures.
• The functions _ctxInitializer() and _ctxFinalizer() use the FREContextInitializer() and FREContextFinalizer() signatures.
• The function _ctxInitializer() uses the ctxType parameter to determine which set of native functions to make available to the ActionScript side. It chooses between the "Basic" functions and the "Advanced" functions.
• Native functions available to the ActionScript side use the FREFunction() signature . These functions are _Basic_helloWorld() , _Advanced_reverseString() , _Advanced_computeNthPrime() , and _Advanced_timeLongOp() .
• The native function _Advanced_timeLongOp() illustrates manipulating an ActionScript Array instance from the native side. The native function receives the array as a parameter.

A sample AIR application that uses the extension is in the following directory in the ZIP file:

To use the extension, an AIR application does the following:

• Creates an instance of one of the extension classes: Basic or Advanced.
• Calls methods of the created class instance.

For example, the following code calls the extension's helloWorld() method when the application user selects the appropriate button in the AIR application's display:

The following code calls the extension's reverseString() method when the application user selects the appropriate button:

For more information about developing native extensions for Adobe AIR, see:

• Extending Adobe AIR
• Developing Native Extensions for Adobe AIR
• Adobe native extension samples

For more information about using a native extension in an AIR application, see:

• Using native extensions for Adobe AIR