I am trying to update the URI written onto an NFC device. I am essentially appending some value from an edittext on the Android app’s screen.

However, whenever I move the NFC device too quickly – the previous URI value gets erased leaving the device in an unusable state. This happens very rarely but it does occur especially in cases where I do multiple NFC swipes within a few seconds (Same Android phone and same NFC device).

I have included the sample code below (I have intentionally kept the URI manipulation code intact as there is a possibility that I’m doing too many things in a short duration which may be partially causing the issue to occur more frequently).

MainActivity.java:

package my.package.name;


import static my.package.name.NfcData.URI_PATTERN;

import android.app.PendingIntent;
import android.content.Intent;
import android.content.IntentFilter;
import android.net.Uri;
import android.nfc.NdefMessage;
import android.nfc.NdefRecord;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.nfc.tech.Ndef;
import android.os.Bundle;
import android.util.Log;
import android.webkit.WebView;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

import java.nio.charset.StandardCharsets;
import java.util.Arrays;

public class MainActivity extends AppCompatActivity {

    private NfcAdapter nfcAdapter;
    private TextView myTextView;
    private final String LOG_TAG = MainActivity.class.getName();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myTextView = findViewById(R.id.myTextView);
        nfcAdapter = NfcAdapter.getDefaultAdapter(this);
    }

    @Override
    protected void onResume() {
        super.onResume();
        if (nfcAdapter != null) {
            PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this, this.getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), PendingIntent.FLAG_MUTABLE);
            IntentFilter tagDetected = new IntentFilter(NfcAdapter.ACTION_TAG_DISCOVERED);
            tagDetected.addCategory(Intent.CATEGORY_DEFAULT);
            IntentFilter writeTagFilters[] = new IntentFilter[]{tagDetected};
            nfcAdapter.enableForegroundDispatch(this, pendingIntent, writeTagFilters, null);
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        if (nfcAdapter != null) {
            nfcAdapter.disableForegroundDispatch(this);
        }
    }

    private void writeNfcDataToDevice(Intent intent, String myString) {
        try {
            Tag nfcTag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
            NfcData nfcData = new NfcData(intent);
            if (URI_PATTERN.matcher(String.valueOf(nfcData.getUri())).matches()) {
                String preExistingUrlStr = nfcData.getUri().toString();
                Uri preExistingUri = Uri.parse(preExistingUrlStr);
                Uri newUri = preExistingUri.buildUpon().clearQuery().appendQueryParameter(NfcData.MY_PARAM, myString).build();
                NdefMessage uriNdefMessage = createUriNdefMessage(newUri);
                Ndef ndef = Ndef.get(nfcTag);
                ndef.connect();
                ndef.writeNdefMessage(uriNdefMessage);
                NdefMessage ndefMessage = ndef.getNdefMessage();
                ndef.close();
                Log.d(LOG_TAG, "NFC write successful !");
            } else {
                Log.d(LOG_TAG, "nSomething Went wrong. URI pattern does not match:" + nfcData.getUri());
            }
        }catch (Exception exception) {
            Log.e(LOG_TAG, "nSomething Went wrong: " + exception.toString());
        }
    }

    @Override
    protected void onNewIntent(Intent intent) {
        super.onNewIntent(intent);
        if (intent != null && (NfcAdapter.ACTION_TAG_DISCOVERED.equals(intent.getAction()))) {
            writeNfcDataToDevice(intent, myTextView.getText().toString().trim());
        }
    }

    public NdefMessage createUriNdefMessage(Uri uri) {
        NdefRecord record = NdefRecord.createUri(uri);
        NdefMessage msg = new NdefMessage(new NdefRecord[]{record});
        return msg;
    }

}

NfcData.java:

package my.package.name;

import android.content.Intent;
import android.net.Uri;
import android.nfc.NdefMessage;
import android.nfc.NdefRecord;
import android.nfc.NfcAdapter;
import android.os.Parcelable;

import java.util.regex.Pattern;

public final class NfcData {

    private final Uri mUri;
    public static final String MY_PARAM = "xyz";
    static Pattern URI_PATTERN = Pattern.compile("^https?://www.mywebsite.com/ax/([0-9A-Fa-f]{12})(?:\?.*)?$");
    // both http and https protocol accepted
    // domain name www.mywebsite.com
    // string "/ax/"
    // 12 compulsory characters that may be any digit from 0 to 9 or A through F or a through f (used to denote bluetooth address)
    // Any text/characters beyond the above are optional

    public Uri getUri() {
        return mUri;
    }

    public NfcData(Intent intent) {
        Uri uri = null;
        Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
        if (rawMsgs != null) {
            for (Parcelable parcelable : rawMsgs) {
                if (!(parcelable instanceof NdefMessage)) continue;
                NdefMessage msg = (NdefMessage) parcelable;
                for (NdefRecord record : msg.getRecords()) {
                    uri = record.toUri();   
                    if(uri != null {
                       this.mUri = uri;  
                       break;
                    }          
                }
            }
        }
    }
}