AAR Record in NFC: Where's The Payload?

问题

According to this answer, and validated by testing, when you use Android Beam to push over an NFC message containing an AAR record, the receiving device will start the MAIN/LAUNCHER activity for the app specified in the AAR.

That MAIN/LAUNCHER Intent does not contain the NfcAdapter.EXTRA_NDEF_MESSAGES extra. Hence, the data that we went through all the trouble to beam over appears to be lost if you use AAR.

Is there some way to get the NFC messages that triggered the app to be started in this scenario?

And if the answer is "no", then what is the use case of AAR? I can see where it might be helpful when the desired app does not exist on the receiving device (brings up Play Store), but then once the app is installed, AAR foils any attempt to deliver data from one device to the other, which is kinda the point behind NFC.

Thanks!

回答1:

At the risk of answering my own question, one recipe for getting this to work (apparently) is:

• Have the Beam sender use an NFC message with two NFC records, the first containing something for a unique MIME type, the second being the AAR

• Have the Beam recipient have an <intent-filter> on the activity that responds to the first NFC record, such as via:

      <intent-filter>
          <action android:name="android.nfc.action.NDEF_DISCOVERED"/>
  
          <category android:name="android.intent.category.DEFAULT"/>
  
          <data android:mimeType="application/vnd.commonsware.webbeam"/>
      </intent-filter>
  

If the app already exists, the NDEF_DISCOVERED Intent will be used, and the recipient can pick up the NFC message and pull out the data from the initial record. If the app does not exist, the AAR will kick in, bringing up the Play Store (whether your app is distributed through the Play Store or not).

This is the recipe shown in the Android Beam example on the developer site.

回答2:

From a look at the docs it would seem the use-case is guaranteeing that your application is launched from the NFC event. A second use-case would basically providing a way for the phone to know which app it needs to read a tag.

Couple of questions If you use two records: first normal, second AAR how does the activity get launched? I would expect you'd be started via the tag dispatch intent. Does the AAR intent contain anything that gets you the Tag? I'm thinking you could manua

来源：https://stackoverflow.com/questions/10887275/aar-record-in-nfc-wheres-the-payload