tags - TagLostException when reading NFC-F card on Android -


i'm developing android application needs read nfc card (the card technology nfc-f). there, following exception:

android.nfc.taglostexception: tag lost.

here code:

private void handleintent(intent intent) {     string action = intent.getaction();     if (nfcadapter.action_ndef_discovered.equals(action)) {      } else if (nfcadapter.action_tech_discovered.equals(action)) {      } else if(nfcadapter.action_tag_discovered.equals(action)) {          tag tag = intent.getparcelableextra(nfcadapter.extra_tag);         if (tag != null) {             nfcf nfcf = nfcf.get(tag);             try {                 nfcf.connect();                 byte[] auto_polling_start = {(byte) 0xe0, 0x00, 0x00, 0x40, 0x01};                 byte[] response = nfcf.transceive(auto_polling_start);                 nfcf.close();             } catch (exception e) {                 e.printstacktrace();                 mtextview.settext(e.tostring());             }         }     } }

can me regarding issue?

you receive taglostexception because send invalid command tag. since nfc-f tags remain silent upon reception of invalid commands, android cannot distinguish between actual loss of communication or negative response unsupported/invalid command , throws taglostexception in both cases.

valid felica (nfc-f) commands have form

 +----------+----------+------------------+-----------------------------------------------+ | len      | command  | idm              | parameter                                     | | (1 byte) | (1 byte) | (8 bytes)        | (n bytes)                                     | +----------+----------+------------------+-----------------------------------------------+

you assemble them following method:

public byte[] transceivecommand(nfcf tag, byte commandcode, byte[] idm, byte[] param) {     if (idm == null) {         // use system idm         idm = tag.gettag().getid();     }     if (idm.length != 8) {         idm = arrays.copyof(idm, 8);     }      if (param == null) {         param = new byte[0];     }      byte[] cmd = new byte[1 + 1 + idm.length + param.length];      // len: fill placeholder     cmd[0] = (byte)(cmd.length & 0x0ff);       // cmd: fill placeholder     cmd[1] = commandcode;      // idm: fill placeholder     system.arraycopy(idm, 0, cmd, 2, idm.length);      // param: fill placeholder     system.arraycopy(param, 0, cmd, 2 + idm.length, param.length);      try {         byte[] resp = tag.transceive(cmd);         return resp;     } catch (taglostexception e) {         // warn: tag-loss cannot distinguished unknown/unexpected command errors     }      return null; }

for instance, command should succeed on tags request system code command (0x0e):

nfcf.connect(); byte[] resp = transceivecommand(nfcf, (byte)0x0c, null, null); nfcf.close();

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