The most used NFC message format on Android is the NDEF format.
- NFC is the radio transmission technology, much like your wifi network card
- NDEF is the payload format, much like a video you're downloading off the Internet
Other formats to NDEF are specified with different domains of functionality, for example secure access cards. See this for a longer introduction to NFC.
The NDEF message format is a binary format in which an NDEF message contains a list of NDEF records, much like a video file contains both audio and picture tracks.
You can make your own custom record types, but there is already standardized a very useful set of records:
- absolute URI (links)
- external type (namespaced/typed data)
- Android Application Record
- mime media (xml, image, etc)
- well-known
- URI
- text (text with language)
- smart poster (online action)
- connection handover records (wifi, bluetooth, etc)
and more.
The Android Application Record is especially important since it lets the NDEF message author specify precisely for which application the message is intended. So if that app is installed and such an NFC tag is scanned, the app launches. If not, Google Play launches to the to-be launched app page, and user can chose to install it (or not).
As the below resources will get you started on sending and receiving messages, you might want to start by getting to know the NDEF format.
A good, hands-on way to learn is to create some records in the editor hosted on this site, install and try the tutorial, then do some experimentation in the editor on your own.
The editor supports most of the known NDEF Record types, and probably all the ones you will need.
The Android NFC API is specified here. Note that NDEF classes are supported but byte-array based.
From version 2.3.3, NFC functionality has been included in Android. Some changes were introduced in 4.0, notably Android Application Records.
More changes were introduced in 4.1, mostly concerning push (beam) messaging.
The emulator does not currently support NFC in/out, so you will need an actual NFC device. Getting some tags or even an NFC terminal for experimentation is also recommended. You can also use two NFC-phones.
To some extent, NFC messaging can be emulated using broadcast intents like in the FakeTagsActivity of the NFCDemo project in the Android samples. This is supported by our NFC Developer app and documented here.
For a soft learning curve, check out this entry-level workshop.
There is a boilerplate Eclipse project for Android included within the download section of this project.
For dynamic reading and writing of NDEF messages at runtime, check out NDEF Tools for Android. This library has higher-level functionality than the current Android NDEF byte-array-based implementation.
If you are into interacting Android devices with NFC readers (terminals) and such, you might also check out NFC Tools for Java.