how do you read the unique ID of an NFC tag on android?

Question

Tag myTag = (Tag) intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
Log.i("tag ID", myTag.getId().toString());

This gives me an ID like "[B@40521c40" but this ID changes every read.

Any help would be greatly appreciated.

Thanks.

Answer 1

you still need to convert the byte to string:

private String bytesToHexString(byte[] src) {
    StringBuilder stringBuilder = new StringBuilder("0x");
    if (src == null || src.length <= 0) {
        return null;
    }

    char[] buffer = new char[2];
    for (int i = 0; i < src.length; i++) {
        buffer[0] = Character.forDigit((src[i] >>> 4) & 0x0F, 16);  
        buffer[1] = Character.forDigit(src[i] & 0x0F, 16);  
        System.out.println(buffer);
        stringBuilder.append(buffer);
    }

    return stringBuilder.toString();
}

Answer 2

I ran in to similar issue and could resolve it. The issue is the conversion to string.

myTag.getId() returns byte array. You should convert these bytes to hex string. I used the following function that I found here in stackoverflow.com

    final protected static char[] hexArray = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
public static String bytesToHex(byte[] bytes) {
    char[] hexChars = new char[bytes.length * 2];
    int v;
    for ( int j = 0; j < bytes.length; j++ ) {
        v = bytes[j] & 0xFF;
        hexChars[j * 2] = hexArray[v >>> 4];
        hexChars[j * 2 + 1] = hexArray[v & 0x0F];
    }
    return new String(hexChars);
}