Using Fingerprint native extension

Fingerprint authentication enables an end-user to use their fingerprint as passcode. With the release of Android 6.0, Google has introduced new APIs to authenticate users by using their fingerprint scans on supported devices.

Fingerprint Native Extension allows an ActionScript developer to access Android's Fingerprint APIs in the AIR app. This article explains how to use this Fingerprint native Extension in your AIR app using sample project files that are available in the attached FingerprintANE.zip file. The zip file contains the following:

• The ActionScript library in the directory FingerprintLibrary: This directory contains the Flash Builder project for creating the ActionScript side of the Fingerprint extension.
• The Android native library in the directory FingerprintAndroidLibrary: This directory contains an Eclipse project for creating Android native side of the Fingerprint extension. To build the eclipse project, you need to first copy FlashRuntimeExtension.jar from <AIR_SDK>/lib/android/ to the directory FingerprintAndroidLibrary/libs/.
• A directory called ReadyToUseExtension: This directory contains everything the AIR you need as a developer to use native extension: the ANE file, the SWC file, and a text file that contains the extension ID.
• A directory called FingerprintTest: This directory contains a sample AIR application that uses the Fingerprint native extension. 

The Fingerprint class in the ActionScript library provides the following public methods:

• public function authenticateFingerPrint( ):void

• public function isSupported( ):Boolean

The AIR application can create many instances of the Fingerprint class. However, the Fingerprint class creates only one ExtensionContext class instance, which is shared by all the Fingerprint instances.

To use Fingerprint ANE, follow these steps:

1. First create a sample AIR application. You can use the sample project FingerprintTest available in the attached zip for your reference.
2. Next, add a reference to the ActionScript library in your project. Right-click the project, choose Properties, and then select ActionScript Build Path on the left panel. Click Add SWC and point to the FingerprintLibrary.swc available in ReadyToUseExtension folder of the attached zip file.

3. Double-click Link Type and choose External in the Library Path Item Options dialog and click Ok. This changes the Link Type of the SWC to External. 

4. Add the ANE file (Fingerprint.ane available in ReadyToUseExtension folder of the attached zip file) to your project.
5. To use Fingerprint ANE, create a Fingerprint object to call authenticateFingerPrint() method and also add event handler provided by the ANE.

6. The ANE also contains isSupported() method to check whether the Fingerprint Authentication is supported by the Android device or not. The method returns true if a device is supported, otherwise false. 

6. Be sure to import the following ActionScript library classes:
   

7. Write the response for the AuthenticateStatus method call. To do so, add the following function:
   

You may receive the following combination of values for event.status and event.statusReason based on the Fingerprint authentication of a user.

• If a user is authenticated successfully (fingerprint is recognized), then the value of event.status will be Authenticated and event.statusReason will be Authorized User.
• If a user is not authenticated (fingerprint is not recognized), then the value of event.status will be Failed and event.statusReason will be Unauthorized User.
• In some of the cases like cancellation of authentication process or on pressing back button, the value of event.status will be Error and event.statusReason will be Error Occured:Fingerprint operation canceled.

Android Applications

To use Fingerprint APIs on Android 6.0, include the USE_FINGERPRINT permission in your application descriptor file:

<uses-permission android:name="android.permission.USE_FINGERPRINT "/>

The Android native library is implemented in Java, using the native extension Java API. The classes which implement FREFunction get FREContext object as the first parameter and FREObject array as the second parameter in their call() method. The native library includes the following classes:

FingerprintExtension implements FREExtension: This class contains the createContext() method. This method is called by the AIR runtime when ExtensionContext.createExtensionContext() is invoked on the ActionScript side; it returns a FingerprintExtensionContext class instance. The initialize() and dispose() methods are called by the AIR runtime on extension initialization and destruction respectively.

FingerprintExtensionContext extends FREContext: This class contains the getFunctions() method. This is an abstract method returning a Map Object functionMap that associates the extension function keys to the native FREFunction implementations.

FingerprintCheckFunction implements FREFunction: This class is mapped to showFingerprintFunction function key in the FingerprintExtensionContext class. It first checks whether the Fingerprint has been enrolled or not. If Fingerprint exists, it generates the keystore and launches the dialog for Fingerprint Authentication.

FingerprintSupportFunction implements FREFunction: This class is mapped to FingerprintSupportFunction function key in the FingerprintExtensionContext class. It checks whether the current Android Version is above Lollipop or not and then it checks whether the device hardware supports Fingerprint scanning or not. It returns true if supported, otherwise false.

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.