Keeping your C native code reusable and independent of AIR

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When you make a native extension using the AIR C API, your native code tends to have two parts:

  • one that’s concerned with exposing functionality in a way that AIR can call, in other words, dependent on the AIR C API;
  • functional part, which deals with the platform-specific stuff. This part of your code doesn’t (and shouldn’t) care about whether it’s used in an AIR native extension, a purely native app or something else.

Ideally you want to keep the dependency between these two parts one-directional: the AIR-concerned part should depend on the functional part, but the functional part should not know about and depend on AIR. If you decide to reuse your, say camera or speech recognition functionality, in another project that’s not AIR-related , you don’t want to force that to include the AIR C API.

So, what happens if you need to dispatch an event from the functional part of your code? Say, the camera refused to start or the speech processor is ready with results and you want you alert AIR to this…

Do you make your functional code include FlashRuntimeExtensions.h and call this?

No way.

Encapsulate thy code

So how do you send an event from the functional part of your code without making it dependent on FlashRuntimeExtensions.h and the AIR C API?

Here is one neat way:

1. Encapsulate the event dispatching in your AIR-dependent code by defining a function that takes the relevant event information and doesn’t require the caller to pass in a FREContext instance or expect a FREResult in return:

Here g_ctx is a pointer to the ExtensionContext that your AIR-dependent code keeps. 

2. Make sendMessage() available  for calling from your AIR-independent code by declaring it as an extern function (in your AIR-independent code):

3. Call sendMessage() from your AIR-independent code. For example:

What else?

See how to send events from Objective-C to ActionScript.

See how to send events from Java to ActionScript.

Do you need a copy of FlashRuntimeExtensions.h in your project?

Over to you

What coding and design principles do you adhere to?

Tell us in the comments below.

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