Android NFC framework introduction and develop guide(15)

Android system NFC framework introduction and develop guide

Android Application Records

Introduced in Android 4.0 (API level 14), an Android Application Record (AAR) provides a

stronger certainty that your application is started when an NFC tag is scanned. An AAR has the package name of an application embedded inside an NDEF record. You can add an AAR to any NDEF record of your NDEF message, because Android searches the entire NDEF message for AARs. If it finds an AAR, it starts the application based on the package name inside the AAR. If the application is not present on the device, Android Market is launched to download the application.

AARs are useful if you want to prevent other applications from filtering for the same intent and potentially handling specific tags that you have deployed. AARs are only supported at the

application level, because of the package name constraint, and not at the Activity level as with If a tag contains an AAR, the tag dispatch system dispatches in the following manner:

1. Try to start an Activity using an intent filter as normal. If the Activity that matches the

intent also matches the AAR, start the Activity.

2. If the Activity that filters for the intent does not match the AAR, if multiple Activities can

handle the intent, or if no Activity handles the intent, start the application specified by the AAR.

3. If no application can start with the AAR, go to the Android Market to download the

application based on the AAR.

Note:is discovered. With this method, the activity must be in the foreground to override AARs and the intent dispatch system.

If you still want to filter for scanned tags that do not contain an AAR, you can declare intent filters as normal. This is useful if your application is interested in other tags that do not contain an AAR. For example, maybe you want to guarantee that your application handles proprietary tags that you deploy as well as general tags deployed by third parties. Keep in mind that AARs are specific to Android 4.0 devices or later, so when deploying tags, you most likely want to use a

combination of AARs and MIME types/URIs to support the widest range of devices. In addition, when you deploy NFC tags, think about how you want to write your NFC tags to enable support for the most devices (Android-powered and other devices). You can do this by defining a relatively unique MIME type or URI to make it easier for applications to distinguish.

Android provides a simple API to create an AAR, createApplicationRecord(). All you need to do is embed the AAR anywhere in your NdefMessage. You do not want to use the first record of your NdefMessage, unless the AAR is the only record in the NdefMessage. This is because