Android NFC 读取记录得到 null Ndef 记录

Question

I am a junior android developper working on a Nfc Reader project. And I use Mifare Cards. I can only read the UID for the card but unable to read records that I wrote using Nfc Tools with my app but it gives me a null when logging the Ndef value in my console. Any help? Thanks in advance Here's my code

public class MainActivity extends AppCompatActivity {
private TextView mNfcText;
private String mTagText;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mNfcText = (TextView) findViewById(R.id.textME);
}

@Override
public void onNewIntent(Intent intent) {
    super.onNewIntent(intent);
    Tag detectedTag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
   
    Ndef ndef = Ndef.get(detectedTag);
    System.out.println("NDEF >>>"+ndef); //gives null
    readNfcTag(intent);
    mNfcText.setText(mTagText);
}

/**
 * NFC READ
 */
private void readNfcTag(Intent intent) {
    if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(intent.getAction())) {
        Parcelable[] rawMsgs = intent.getParcelableArrayExtra(
                NfcAdapter.EXTRA_NDEF_MESSAGES);
        NdefMessage msgs[] = null;
        int contentSize = 0;
        if (rawMsgs != null) {
            msgs = new NdefMessage[rawMsgs.length];
            for (int i = 0; i < rawMsgs.length; i++) {
                msgs[i] = (NdefMessage) rawMsgs[i];
                contentSize += msgs[i].toByteArray().length;
            }
        }
        try {
            if (msgs != null) {
                NdefRecord record = msgs[0].getRecords()[0];
                String textRecord = parseTextRecord(record);
                mTagText += textRecord + "\n\ntext\n" + contentSize + " bytes";
            }
        } catch (Exception e) {
        }
    }
}

/**
 * PArser
 */
public static String parseTextRecord(NdefRecord ndefRecord) {
    
    if (ndefRecord.getTnf() != NdefRecord.TNF_WELL_KNOWN) {
        return null;
    }
    if (!Arrays.equals(ndefRecord.getType(), NdefRecord.RTD_TEXT)) {
        return null;
    }
    try {
       
        byte[] payload = ndefRecord.getPayload();
        String textEncoding = ((payload[0] & 0x80) == 0) ? "UTF-8" : "UTF-16";
        int languageCodeLength = payload[0] & 0x3f;
        String languageCode = new String(payload, 1, languageCodeLength, "US-ASCII");
        String textRecord = new String(payload, languageCodeLength + 1,
                payload.length - languageCodeLength - 1, textEncoding);
        System.out.println("Text "+textRecord);
        return textRecord;
    } catch (Exception e) {
        throw new IllegalArgumentException();
    }
}

Answer 1

You don't specify exact which type of card you are using (Model type of the card) but Most cards described as "Mifare" are not actual fully NFC standards compliant.

This especially is the case if it is a Mifare Classic Type card.

So there are 2 possible reason for your problem.

1)Mifare classic cards have a proprietary method of storing Ndef Data on them and not every phone hardware supports either reading Ndef data from them or supports reading them at anything other than the NfcA low level protocol. And you would have to implement reading/writing Ndef data yourself using the proprietary method.

It would be better to use a NFC standards compliant Card like one of the NTAG21x series instead.

2)You don't seemed to have configured your code to actually ask the system to send you data when it sees a card via Manifest entries when your app is not running or via one of the 2 foreground detection methods when your app is already running (See https://stackoverflow.com/a/72152878/2373819 for more details)