How can I send a text string to another device via NFC?

Question

I want to create a mini app just to read an NFC tag and later send to another device on Android. That part is done already and I can read the tag and I can print the string on a EditText. But I also want to send the text that I have read from that tag to another device with NFC. How can I do that?

//I have this code here when a tag is discovered...
@Override
protected void onNewIntent(Intent intent) {
    if (intent.getAction().equals(NfcAdapter.ACTION_TAG_DISCOVERED)) {
        String result = "";
        result = ByteArrayToHexString(intent.getByteArrayExtra(NfcAdapter.EXTRA_ID));
        myTag = result;
        txtTag.setText(myTag);

    }
}

How can I send the text string to another device via NFC?

Answer 1

What you want to do is simply not possible with Android right no (and probably won't be in future).

You currently read the anti-collision identifier (UID, PUPI, or whatever it is called for that specific tag platform that you read):

result = ByteArrayToHexString(intent.getByteArrayExtra(NfcAdapter.EXTRA_ID));

The anti-collision identifier is part of a very low protocol layer. While Android does support host-based card emulation (see Android HCE), the Android API has no means to control such low-level parameters as the UID. Typically, its also not possible to change that information on NFC tags.

Note that if your tag also contains some high-level data in NDEF format you could obtain that using:

Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
NdefMessage msg = null;
if ((rawMsgs != null) && (rawMsgs.length > 0)) {
    msg = (NdefMessage)rawMsgs[0];
}
if (msg != null) {
    // do something with the received message
}

Android does support storing these NDEF messages on (writable) NFC tags and it also supports sending NDEF messages to other NFC devices (see Beaming NDEF Messages to Other Devices).

• E.g. to store an NDEF message on an NFC tag you could use:

  Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
  Ndef ndef = Ndef.get(tag);
  if (ndef != null) {
      try {
          ndef.connect();
          ndef.writeNdefMessage(msg);
      } finally {
          ndef.close();
      }
  } else {
      NdefFormatable ndefFormatable = NdefFormatable.get(tag);
      if (ndefFormatable != null) {
          try {
              ndefFormatable.connect();
              ndefFormatable.format(message);
          } finally {
              ndefFormatable.close();
          }
      }
  }
  

• Or in order to send the message to another NFC device through peer-to-peer mode (Android Beam), you could use:

   NfcAdapter nfcAdapter = NfcAdapter.getDefaultAdapter(this);
   nfcAdapter.setNdefPushMessage(msg, this);