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Backward compatibility and the extension’s public interfaces
A best practice is to maintain backward compatibility in
your extension’s ActionScript public interfaces. Continue to support
the extension’s classes, methods, properties, and events in all
subsequent versions of the extension.
Device-bundled extensions have a more complex issue with regard
to backward compatibility. Sometimes, the
behavior
of an
extension is different between versions of an extension. For example,
a particular method returns a value with a new meaning in a new
version of the extension. When this behavior occurs for device-bundled
extensions, an application can stop working correctly. This problem
can occur if the application was built with a version of the extension
that behaves differently than the version of the extension installed
on the device. In this case, the application expects one behavior,
but the installed extension provides a different behavior.
In such cases, the extension installed on the device can determine
how to proceed. The extension can do the following:
-
Look up the extension version that the AIR application
was built with as well as the version installed on the device.
-
Determine whether the extension’s behavior is different in
the two versions.
-
If the AIR application was built with an older version of
the extension, revert to the older version’s behavior.
To look up the extension version number that the application
was built with, do the following:
-
Get the application installation directory using
File.applicationDirectory
.
-
Use the File class APIs to access the extension.xml file
of the extension that the application built against. The file is
at:
<application directory>/META-INF/AIR/extensions/<extensionID>/META-INF/ANE/extension.xml
-
Read the contents of the extension.xml file and find the
value of the
<versionNumber>
element.
To look up the installed extension’s version number, do the following:
-
Use the static method
ExtensionContext.getExtensionDirectory()
to
get the base directory for the extension.
-
Use the File class APIs to access the extension.xml file
of the extension installed on the device. The file is at:
<extension base directory>/META-INF/ANE/extension.xml
-
Read the contents of the extension.xml file and find the
value of the
<versionNumber>
element.
Backward compatibility and the device’s application store
An AIR application that was built with a newer version
of the extension than is installed on the device is typically not
available on the device. The application is not available because
of how device manufacturers handle requests from the device’s application
store to a server to download such an application. Adobe recommends
the following handling to the device manufacturers:
-
Consider the case when the server downloads an application
that uses a newer version of the extension. The server also downloads
the newer version of the extension. The device’s application store
installs both the application and the newer version of the extension.
-
Consider the case when the server cannot download a newer
version of the extension. The server also does not download the
application that uses that version of the extension. The device’s
application store handles the scenario gracefully, informing the
end user as needed.
-
Consider the case when the server downloads an application
that uses a newer version of the extension, but does not download
the newer version of the extension. The device’s application store
does not allow the end user to run the application. The application
store handles the scenario gracefully, informing the end user as
needed.
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