Answer on SO:
You are using the Intent-based NFC detection technology that may be not the best option, I'm preferring the more modern Reader Mode for accessing NFC tags.
As there are a lot of questions here on Stackoverflow.com regarding this topic I'm providing a sample app how to work with the Reader Mode. The complete (Java) source is available here: https://github.com/AndroidCrypto/AndroidBasicNfcReader.
I read that you are working with Kotlin but in AndroidStudio it is just a simple click to convert the class to Kotlin code.
To run the code you need to add the <uses-permission android:name="android.permission.NFC" /> line to your AndroidManifest.xml and that's it:
package de.androidcrypto.androidbasicnfcreader;
import android.content.Intent;
import android.media.AudioManager;
import android.media.ToneGenerator;
import android.nfc.FormatException;
import android.nfc.NdefMessage;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.nfc.tech.Ndef;
import android.nfc.tech.NfcA;
import android.nfc.tech.NfcV;
import android.os.Bundle;
import android.provider.Settings;
import android.widget.TextView;
import android.widget.Toast;
import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
public class MainActivity extends AppCompatActivity implements NfcAdapter.ReaderCallback {
private TextView textView;
private NfcAdapter myNfcAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
EdgeToEdge.enable(this);
setContentView(R.layout.activity_main);
ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {
Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom);
return insets;
});
textView = findViewById(R.id.textView);
myNfcAdapter = NfcAdapter.getDefaultAdapter(this);
}
/**
* Please note: this method is NOT running in User Interface (UI) Thread, so you cannot write directly
* to any TextView, Toasts or other elements on your activity. Please use runOnUiThread instead:
* runOnUiThread(() -> {
* Toast.makeText(getApplicationContext(), message, Toast.LENGTH_SHORT).show();
* });
*
* @param tag
*/
@Override
public void onTagDiscovered(Tag tag) {
String output = "";
String lineDivider = "--------------------";
output += "NFC tag detected" + "\n";
// examine tag
byte[] tagUid = tag.getId();
output += "Tag UID length: " + tagUid.length + " UID: " + bytesToHex(tagUid) + "\n";
String[] techlist = tag.getTechList();
output += lineDivider + "\n";
output += "The TechList contains " + techlist.length + " entry/ies:" + "\n";
for (int i = 0; i < techlist.length; i++) {
output += "Entry " + i + ": " + techlist[i] + "\n";
}
output += lineDivider + "\n";
output += tag.toString() + "\n";
output += lineDivider + "\n";
// if the tag uses the NfcA class I'm connecting the tag now this class
// I'm trying to use the NfcA class, if it is not supported by the tag an exception is thrown
NfcA nfcA = null;
nfcA = NfcA.get(tag);
if (nfcA == null) {
output += "This tag is NOT supporting the NfcA class" + "\n";
output += lineDivider + "\n";
} else {
// I'm trying to get more information's about the tag and connect to the tag
byte[] atqa = nfcA.getAtqa();
byte sak = (byte) nfcA.getSak();
int maxTransceiveLength = nfcA.getMaxTransceiveLength();
output += "-= NfcA Technology =-" + "\n";
output += "ATQA: " + bytesToHex(atqa) + "\n";
output += "SAK: " + byteToHex(sak) + "\n";
output += "maxTransceiveLength: " + maxTransceiveLength + "\n";
output += lineDivider + "\n";
try {
nfcA.connect();
output += "Connected to the tag using NfcA technology" + "\n";
output += lineDivider + "\n";
nfcA.close();
} catch (IOException e) {
output += "NfcA connect to tag IOException: " + e.getMessage() + "\n";
output += lineDivider + "\n";
}
}
// connect to NfcV class (e.g. ICODE tags use this technology
NfcV nfcV = null;
nfcV = NfcV.get(tag);
if (nfcV == null) {
output += "This tag is NOT supporting the NfcV class" + "\n";
output += lineDivider + "\n";
} else {
byte dsfId = nfcV.getDsfId();
int maxTransceiveLength = nfcV.getMaxTransceiveLength();
output += "-= NfcV Technology =-" + "\n";
output += "DsfId: " + byteToHex(dsfId) + "\n";
output += "maxTransceiveLength: " + maxTransceiveLength + "\n";
output += lineDivider + "\n";
try {
nfcV.connect();
output += "Connected to the tag using NfcV technology" + "\n";
output += lineDivider + "\n";
nfcV.close();
} catch (IOException e) {
output += "NfcV connect to tag IOException: " + e.getMessage() + "\n";
output += lineDivider + "\n";
}
}
// trying to read NDEF content
Ndef ndef = null;
ndef = Ndef.get(tag);
if (ndef == null) {
output += "This tag is NOT supporting the NDEF class" + "\n";
output += lineDivider + "\n";
} else {
try {
ndef.connect();
output += "Connected to the tag using NDEF technology" + "\n";
output += lineDivider + "\n";
NdefMessage ndefMessage = ndef.getNdefMessage();
String ndefMessageString = ndefMessage.toString();
byte[] ndefMessageBytes = ndefMessage.toByteArray();
output += "NDEF message: " + ndefMessageString + "\n";
if (ndefMessageBytes != null) {
output += "NDEF message: " + bytesToHex(ndefMessageBytes) + "\n";
output += "NDEF message: " + new String(ndefMessageBytes, StandardCharsets.UTF_8) + "\n";
}
output += lineDivider + "\n";
ndef.close();
} catch (IOException e) {
output += "NDEF connect to tag IOException: " + e.getMessage() + "\n";
output += lineDivider + "\n";
} catch (FormatException e) {
output += "NDEF connect to tag RunTimeException: " + e.getMessage() + "\n";
output += lineDivider + "\n";
}
}
// final output
String finalOutput = output;
runOnUiThread(() -> {
textView.setText(finalOutput);
});
// output of the logfile to console
System.out.println(output);
// a short information about the detection of an NFC tag after all reading is done
playBeep();
}
/**
* When the activity returns to foreground the ReaderMode gets enabled. Here I'm setting all flags,
* meaning that all NFC technologies are allowed to get detected. If you remove e.g. the NfcA class
* you won't detect NTAG21x tags anymore.
*/
@Override
protected void onResume() {
super.onResume();
if (myNfcAdapter != null) {
if (!myNfcAdapter.isEnabled())
showWirelessSettings();
Bundle options = new Bundle();
// Work around for some broken Nfc firmware implementations that poll the card too fast
options.putInt(NfcAdapter.EXTRA_READER_PRESENCE_CHECK_DELAY, 250);
// Enable ReaderMode for all types of card and disable platform sounds
// The option NfcAdapter.FLAG_READER_SKIP_NDEF_CHECK is NOT set
// to get the data of the tag after reading
myNfcAdapter.enableReaderMode(this,
this,
NfcAdapter.FLAG_READER_NFC_A |
NfcAdapter.FLAG_READER_NFC_B |
NfcAdapter.FLAG_READER_NFC_F |
NfcAdapter.FLAG_READER_NFC_V |
NfcAdapter.FLAG_READER_NFC_BARCODE |
NfcAdapter.FLAG_READER_NO_PLATFORM_SOUNDS,
options);
}
}
/**
* When the activity gets inactive the ReaderMode is disabled
*/
@Override
protected void onPause() {
super.onPause();
if (myNfcAdapter != null)
myNfcAdapter.disableReaderMode(this);
}
/**
* If the onResume() method detects that the NFC option is not enabled this method will forward you
* to the Settings to enable NFC.
*/
private void showWirelessSettings() {
Toast.makeText(this, "You need to enable NFC", Toast.LENGTH_SHORT).show();
Intent intent = new Intent(Settings.ACTION_WIRELESS_SETTINGS);
startActivity(intent);
}
public static String byteToHex(Byte input) {
return String.format("%02X", input);
//return String.format("0x%02X", input);
}
public static String bytesToHex(byte[] bytes) {
if (bytes == null) return "";
StringBuffer result = new StringBuffer();
for (byte b : bytes)
result.append(Integer.toString((b & 0xff) + 0x100, 16).substring(1));
return result.toString();
}
public void playBeep() {
ToneGenerator toneGen = new ToneGenerator(AudioManager.STREAM_MUSIC, 100);
toneGen.startTone(ToneGenerator.TONE_CDMA_PIP, 150);
}
}
Michael