title: Id on Nfc tag not unique?
body: <p>I am reading nfc tags on android phone, there is value which I written to the tag which I read like this:</p>
  
  <pre><code>@Override
  protected String doInBackground(Tag... params) {
      Tag tag = params[0];
  
      Ndef ndef = Ndef.get(tag);
      if (ndef == null) {
          // NDEF is not supported by this Tag.
          return null;
      }
  
      NdefMessage ndefMessage = ndef.getCachedNdefMessage();
  
      NdefRecord[] records = ndefMessage.getRecords();
      for (NdefRecord ndefRecord : records) {
          if (ndefRecord.getTnf() == NdefRecord.TNF_WELL_KNOWN &amp;&amp; Arrays.equals(ndefRecord.getType(), NdefRecord.RTD_TEXT)) {
              try {
                  return readText(ndefRecord);
              } catch (UnsupportedEncodingException e) {
                  Log.e(TAG, "Unsupported Encoding", e);
              }
          }
      }
      return null;
  }
  
  private String readText(NdefRecord record) throws UnsupportedEncodingException {
      byte[] payload = record.getPayload();
      String textEncoding = ((payload[0] &amp; 128) == 0) ? "UTF-8" : "UTF-16";                                               // Get the Text Encoding
      int languageCodeLength = payload[0] &amp; 0063;                                                                         // Get the Language Code
      return new String(payload, languageCodeLength + 1, payload.length - languageCodeLength - 1, textEncoding);          // Get the Text
  }
  </code></pre>
  
  <p>And there should be a unique Id of the NfcTag which is read only, I tried:</p>
  
  <pre><code>     Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
       mNfcId = tag.getId().toString();
  </code></pre>
  
  <p>But this is giving different results on next read !!!
  How can I read the unique read only tag from nfc Tag ?</p>