Reading NFC Tag gets null UID

Question

I am working on an NFC reader app which uses NfcA, MifareUltralight and Ndef technologies. It works fine when I attempt to use sticker tags and by that I mean it reads the serial number correctly. When using another type of tag which according to NFC Tools seems to cover the same technology however the getByteArrayExtra returns null even though the tags have a valid serial number.

On the other hand the last type of tags which I am having issues with does contain NDEF messages.

In short these tags' serial numbers are used to identify users passing by an entry device.

I am quite confused about it and any assistance is welcome. Code is below:

MainActivity:

package org.bogdan.learning.gantopendemo;

import org.bogdan.learning.gantopendemo.util.SystemUiHider;

import android.annotation.TargetApi;
import android.app.Activity;
import android.app.PendingIntent;
import android.app.ProgressDialog;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.res.AssetManager;
import android.media.MediaPlayer;
import android.nfc.NdefMessage;
import android.nfc.NdefRecord;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.nfc.tech.MifareUltralight;
import android.nfc.tech.Ndef;
import android.nfc.tech.NfcA;
import android.os.AsyncTask;
import android.os.Build;
import android.os.Bundle;
import android.os.Handler;
import android.os.Looper;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.sql.SQLException;
import java.util.Arrays;
import java.util.concurrent.TimeUnit;


/**
 * An example full-screen activity that shows and hides the system UI (i.e.
 * status bar and navigation/system bar) with user interaction.
 *
 * @see SystemUiHider
 */
public class MainActivity extends Activity {
    /**
     * Whether or not the system UI should be auto-hidden after
     * {@link #AUTO_HIDE_DELAY_MILLIS} milliseconds.
     */
    private static final boolean AUTO_HIDE = true;

    /**
     * If {@link #AUTO_HIDE} is set, the number of milliseconds to wait after
     * user interaction before hiding the system UI.
     */
    private static final int AUTO_HIDE_DELAY_MILLIS = 3000;

    /**
     * If set, will toggle the system UI visibility upon interaction. Otherwise,
     * will show the system UI visibility upon interaction.
     */
    private static final boolean TOGGLE_ON_CLICK = true;

    /**
     * The flags to pass to {@link SystemUiHider#getInstance}.
     */
    private static final int HIDER_FLAGS = SystemUiHider.FLAG_HIDE_NAVIGATION;

    /**
     * The instance of the {@link SystemUiHider} for this activity.
     */
    private SystemUiHider mSystemUiHider;

    // NFC Related variables go here, namely the adapter and helpers

    public static final String MIME_TEXT_PLAIN = "text/plain";
    public static final String TAG = "EventTAG";
    private NfcAdapter mNfcAdapter; // Used for accessing the NFC Hardware

    // SQLite Variables go here
    private EventTagDataSource dataSource;

    // wait interval before screen is redrawn
    private int miliseconds = 6000;

    // Sound related activities
    private MediaPlayer mediaPlayer;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_gant_open);

        final View controlsView = findViewById(R.id.fullscreen_content_controls);
        final View contentView = findViewById(R.id.fullscreen_content);

        /**
         * Open the database connection
         */
        dataSource = new EventTagDataSource(this);

        try {
            dataSource.open();
        } catch (SQLException exp) {
            Log.d("SQLExp", "SQL Exception ocurred", exp);
        }


        // return the default NFC adapter

        mNfcAdapter = NfcAdapter.getDefaultAdapter(this);

        // is NFC Enabled or not=
        if (mNfcAdapter == null) {
            finish();
            return;
        }

        // is the NFC Reader enabled?
        if (!mNfcAdapter.isEnabled()) {
            Toast.makeText(this, "NFC Reader is not enabled. Please enable and try again", Toast.LENGTH_LONG).show();
        }

        // Set up an instance of SystemUiHider to control the system UI for
        // this activity.
        mSystemUiHider = SystemUiHider.getInstance(this, contentView, HIDER_FLAGS);
        mSystemUiHider.setup();
        mSystemUiHider
                .setOnVisibilityChangeListener(new SystemUiHider.OnVisibilityChangeListener() {
                    // Cached values.
                    int mControlsHeight;
                    int mShortAnimTime;

                    @Override
                    @TargetApi(Build.VERSION_CODES.HONEYCOMB_MR2)
                    public void onVisibilityChange(boolean visible) {
                        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB_MR2) {
                            // If the ViewPropertyAnimator API is available
                            // (Honeycomb MR2 and later), use it to animate the
                            // in-layout UI controls at the bottom of the
                            // screen.
                            if (mControlsHeight == 0) {
                                mControlsHeight = controlsView.getHeight();
                            }
                            if (mShortAnimTime == 0) {
                                mShortAnimTime = getResources().getInteger(
                                        android.R.integer.config_shortAnimTime);
                            }
                            controlsView.animate()
                                    .translationY(visible ? 0 : mControlsHeight)
                                    .setDuration(mShortAnimTime);
                        } else {
                            // If the ViewPropertyAnimator APIs aren't
                            // available, simply show or hide the in-layout UI
                            // controls.
                            controlsView.setVisibility(visible ? View.VISIBLE : View.GONE);
                        }

                        if (visible && AUTO_HIDE) {
                            // Schedule a hide().
                            delayedHide(AUTO_HIDE_DELAY_MILLIS);
                        }
                    }
                });

        // Set up the user interaction to manually show or hide the system UI.
        contentView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (TOGGLE_ON_CLICK) {
                    mSystemUiHider.toggle();
                } else {
                    mSystemUiHider.show();
                }
            }
        });

        // Upon interacting with UI controls, delay any scheduled hide()
        // operations to prevent the jarring behavior of controls going away
        // while interacting with the UI.
        findViewById(R.id.dummy_button).setOnTouchListener(mDelayHideTouchListener);
        findViewById(R.id.dummy_button).setOnLongClickListener(new View.OnLongClickListener() {
            public boolean onLongClick(View view) {
                //Toast.makeText(getApplicationContext(), "Long Click Detected", Toast.LENGTH_LONG).show();
                launchRingDialog(view);
                return false;
            }
        });
        handleIntent(getIntent());
    }

    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);

        // Trigger the initial hide() shortly after the activity has been
        // created, to briefly hint to the user that UI controls
        // are available.
        delayedHide(100);
    }


    /**
     * Touch listener to use for in-layout UI controls to delay hiding the
     * system UI. This is to prevent the jarring behavior of controls going away
     * while interacting with activity UI.
     */
    View.OnTouchListener mDelayHideTouchListener = new View.OnTouchListener() {
        @Override
        public boolean onTouch(View view, MotionEvent motionEvent) {
            if (AUTO_HIDE) {
                delayedHide(AUTO_HIDE_DELAY_MILLIS);
            }
            return false;
        }
    };

    Handler mHideHandler = new Handler();
    Runnable mHideRunnable = new Runnable() {
        @Override
        public void run() {
            mSystemUiHider.hide();
        }
    };

    /**
     * Schedules a call to hide() in [delay] milliseconds, canceling any
     * previously scheduled calls.
     */
    private void delayedHide(int delayMillis) {
        mHideHandler.removeCallbacks(mHideRunnable);
        mHideHandler.postDelayed(mHideRunnable, delayMillis);
    }

    /**
     * onResume - when application returns from standby it reopens database connection
     * and sets up foreground dispatch
     */
    @Override
    protected void onResume() {
        try {
            dataSource.open();
        } catch (SQLException exp) {
            Log.d("SQLExp", "SQL Exception ocurred", exp);
        }
        super.onResume();
        setupForegroundDispatch(this, mNfcAdapter);
    }

    /**
     * onPause - closes database connection, stops foreground despatch and sets application in
     * standby mode.
     */
    @Override
    protected void onPause() {
        dataSource.close();
        stopForegroundDispatch(this, mNfcAdapter);
        super.onPause();
    }

    /**
     * creates a new intent and calles handleIntent(intent) to deal with it.
     *
     * @param intent
     */
    @Override
    protected void onNewIntent(Intent intent) {
        handleIntent(intent);
    }

    /**
     *
     */
    public String uidByteToHexString(byte[] uid) {
        int iCounter, jCounter, in;

        String[] hex = {
                "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F"
        };
        String out = "";

        for (jCounter = 0; jCounter < uid.length; jCounter++) {
            in = uid[jCounter] & 0xff;
            iCounter = (in >> 4) & 0x0f;
            out += hex[iCounter];
            iCounter = in & 0x0f;
            out += hex[iCounter];
        }

        return out;

    }

    /**
     * Handles intent within the application (such as NFC Tag detected)
     *
     * @param intent
     */
    private void handleIntent(Intent intent) {

        String action = intent.getAction();

        if (NfcAdapter.ACTION_TECH_DISCOVERED.equals(action) || NfcAdapter.ACTION_NDEF_DISCOVERED.equals(action)) {
            Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
            new NdefReaderTask().execute(tag);
        }
        /*else if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(action)) {
            Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
            new NdefReaderTask().execute(tag);
        }*/
    }

    /**
     * Method: loadTagsFromFile
     *
     * @param - none
     * @return - void
     * @description - Loads a set of NFC Tags from a given CSV file into the SQLite Database
     */
    public void loadTagsFromFile(String fileName) {

        AssetManager manager = getApplicationContext().getAssets();
        InputStream inStream = null;

        try {
            inStream = manager.open(fileName);
        } catch (IOException exp) {
            exp.printStackTrace();
        }

        // open a buffered reader and start reading from the inputStream
        BufferedReader buffer = new BufferedReader(new InputStreamReader(inStream));
        String line = ""; //current line in our CSV file

        // open a transcation to start mass inserting data
        dataSource.database.beginTransaction();

        try {
            while ((line = buffer.readLine()) != null) {
                String[] columns = line.split(";");

                if (columns.length != 4) {
                    Log.d("CSVParser", "Skipping malformed CSV format");
                    continue;
                }

                dataSource.createEventTag(columns[1].trim(), columns[2].trim(), columns[3]);
            }
        } catch (IOException exp) {
            exp.printStackTrace();
        }

        dataSource.database.setTransactionSuccessful();
        dataSource.database.endTransaction();
    }

    /**
     * Method: launchRingDialog
     * Description: Opens the Ring Dialog and loads the CSV File into the Database
     *
     * @param view
     */
    public void launchRingDialog(View view) {
        final ProgressDialog ringProgressDialog = ProgressDialog.show(this, "Loading NFC Tags ...", "Loading records ...", true);

        ringProgressDialog.setCancelable(true);
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    //Thread.sleep(10000);
                    loadTagsFromFile("nfccodes.csv");

                } catch (Exception e) {
                    Log.d("CSVLoader", "CSV Loader Exception occurred", e);
                }
                ringProgressDialog.dismiss();
            }
        }).start();
    }

    /**
     * Sets up Foreground Dispatch system for the activity and NfcAdapter required
     *
     * @param activity
     * @param adapter
     */
    public static void setupForegroundDispatch(final Activity activity, NfcAdapter adapter) {

        final Intent intent = new Intent(activity.getApplicationContext(), activity.getClass());
        intent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);

        final PendingIntent pendingIntent = PendingIntent.getActivity(activity.getApplicationContext(), 0, intent, 0);

        IntentFilter[] filters = new IntentFilter[1];
        String[][] techList = new String[][]{ new String[] {MifareUltralight.class.getName()},
                                              new String[] {NfcA.class.getName()},
                                              new String[] {Ndef.class.getName()}
                                            };

        filters[0] = new IntentFilter();
        filters[0].addAction(NfcAdapter.ACTION_TECH_DISCOVERED);
        filters[0].addAction(NfcAdapter.ACTION_NDEF_DISCOVERED);
        filters[0].addAction(NfcAdapter.ACTION_TAG_DISCOVERED);


        filters[0].addCategory(Intent.CATEGORY_DEFAULT);

        try {
            filters[0].addDataType(MIME_TEXT_PLAIN);
        } catch (IntentFilter.MalformedMimeTypeException e) {
            throw new RuntimeException("Check your mime type");
        }

        adapter.enableForegroundDispatch(activity, pendingIntent, filters, techList);
    }

    /**
     * Stops the Foreground Dispatch system for specified activity and nfc adapter.
     *
     * @param activity
     * @param adapter
     */
    public static void stopForegroundDispatch(final Activity activity, NfcAdapter adapter) {
        adapter.disableForegroundDispatch(activity);
    }

    /**
     * Internal class used to create an NFC Reading Task, triggered when an NFC card is brought
     * close or in contact to the device's NFC reading system.
     */
    private class NdefReaderTask extends AsyncTask<Tag, Void, String> {

        /**
         * Overriden abstract method that performs the async task of reading the task.
         *
         * @param params
         * @return - the contents of the Tag as String
         */

        @Override
        protected String doInBackground(Tag... params) {
            Tag tag = params[0];
            byte[] uid = getIntent().getByteArrayExtra(NfcAdapter.EXTRA_ID);

            String serialNumber = uidByteToHexString(uid);

            if (serialNumber != null && !serialNumber.isEmpty()) {
                return serialNumber;
            }
            return null;
        }

        /**
         * Reads a NdefRecord and returns the string calculated from the tag's payload taken over as a
         * byte array
         *
         * @param record
         * @return String - the string representation of the NFC Tag's payload
         * @throws UnsupportedEncodingException
         */
        private String readText(NdefRecord record) throws UnsupportedEncodingException {
            byte[] payload = record.getPayload();

            String textEncoding = ((payload[0] & 128) == 0) ? "UTF-8" : "UTF-16";
            int languageCodeLength = payload[0] & 0063;

            return new String(payload, languageCodeLength + 1, payload.length - languageCodeLength - 1, textEncoding);
        }


        /**
         * Overriden method - based on the result (Tag's code) it shows the correct screen,
         * either OK or FAILURE screen, plays a sound and returns app to default screen.
         * <p/>
         * This method is executed after the AsyncTask is finished.
         *
         * @param result
         */
        @Override
        protected void onPostExecute(String result) {
            if (result != null) {
                // Do SOMETHING HERE
                // find the tag which has the same code as result
                EventTag currentTag = dataSource.getEventTag(result);
                if (currentTag != null) {
                    //Toast.makeText(getApplicationContext(), "Welcome " + currentTag.getFullName() + " you are using tag: " + currentTag.getNfcCode(), Toast.LENGTH_LONG).show();
                    findViewById(R.id.fullscreen_content).setBackgroundResource(R.drawable.bggreen);
                    ((TextView) findViewById(R.id.fullscreen_content)).setText(getResources().getString(R.string.txt_tag_ok) + " " + currentTag.getFullName());

                    // create a media player or better just play the music
                    mediaPlayer = MediaPlayer.create(getApplicationContext(), R.raw.gantsound_ok);
                    mediaPlayer.start();

                } else {
                    //Toast.makeText(getApplicationContext(), "Tag with code: " + result + " not found in database", Toast.LENGTH_LONG).show();
                    findViewById(R.id.fullscreen_content).setBackgroundResource(R.drawable.bgred);
                    ((TextView) findViewById(R.id.fullscreen_content)).setText(getResources().getString(R.string.txt_tag_notok));

                    // create a media player or better just play the music
                    mediaPlayer = MediaPlayer.create(getApplicationContext(), R.raw.error);
                    mediaPlayer.start();

                }

                // use a handler here

                final Handler handler = new Handler();

                final Runnable runnable = new Runnable() {
                    public void run() {
                        findViewById(R.id.fullscreen_content).setBackgroundResource(R.drawable.bgblue);
                        ((TextView) findViewById(R.id.fullscreen_content)).setText(getResources().getString(R.string.dummy_content));

                        handler.postDelayed(this, miliseconds);
                    }
                };
                handler.postDelayed(runnable, miliseconds);
            }
            else {

                //Toast.makeText(getApplicationContext(), "Tag with code: " + result + " not found in database", Toast.LENGTH_LONG).show();
                findViewById(R.id.fullscreen_content).setBackgroundResource(R.drawable.bgred);
                ((TextView) findViewById(R.id.fullscreen_content)).setText(getResources().getString(R.string.txt_tag_notok));

                // create a media player or better just play the music
                mediaPlayer = MediaPlayer.create(getApplicationContext(), R.raw.error);
                mediaPlayer.start();

                // use a handler here
                final Handler handler = new Handler();

                final Runnable runnable = new Runnable() {
                    public void run() {
                        findViewById(R.id.fullscreen_content).setBackgroundResource(R.drawable.bgblue);
                        ((TextView) findViewById(R.id.fullscreen_content)).setText(getResources().getString(R.string.dummy_content));

                        handler.postDelayed(this, miliseconds);
                    }
                };
                handler.postDelayed(runnable, miliseconds);
            }
        }
    }
}

Application Manifest:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="my app and package" >

    <!-- Application permissions go here, mainly NFC -->
    <uses-permission android:name="android.permission.NFC" />
    <users-feature android:name="android.hardware.nfc" android:required="true"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:configChanges="orientation|keyboardHidden|screenSize"
            android:label="@string/app_name"
            android:theme="@style/FullscreenTheme" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>

            <!-- NFC Intent Filters -->
            <intent-filter>
                <action android:name="android.nfc.action.TECH_DISCOVERED" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>

            <intent-filter>
                <action android:name="android.nfc.action.NDEF_DISCOVERED" />
                <category android:name="android.intent.category.DEFAULT" />
                <data android:mimeType="text/plain" />
            </intent-filter>

            <intent-filter>
                <action android:name="android.nfc.action.TAG_DISCOVERED" />
                <category android:name="android.intent.category.DEFAULT"/>
            </intent-filter>

            <meta-data android:name="android.nfc.action.TECH_DISCOVERED"
                android:resource="@xml/nfc_tech_filter" />
        </activity>
    </application>

</manifest>

My technologies list:

<?xml version="1.0" encoding="utf-8"?>
<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2">
    <tech-list>
        <tech>android.nfc.tech.Ndef</tech>
    </tech-list>
    <tech-list>
        <tech>android.nfc.tech.NfcA</tech>
    </tech-list>
    <tech-list>
        <tech>android.nfc.tech.MifareUltralight</tech>
    </tech-list>
</resources>

Answer 1

Your AsyncTask uses

byte[] uid = getIntent().getByteArrayExtra(NfcAdapter.EXTRA_ID);

to obtain the anti-collision identifier (UID) of the scanned tag.

The problematic part here is getIntent(). This will use the last intent that was set with setIntent() (or if set intent is never used as in your code, it will use the intent that started your activity). So if you started your activity using its launcher icon, getIntent() will return the launcher intent and no NFC discovery intent. Hence, there won't be an intent extra named NfcAdapter.EXTRA_ID.

So what you could do is to pass the whole intent instead of just the tag object to the AsyncTask:

private void handleIntent(Intent intent) {
    String action = intent.getAction();

    if (NfcAdapter.ACTION_TECH_DISCOVERED.equals(action) ||
        NfcAdapter.ACTION_NDEF_DISCOVERED.equals(action)) {
        new NdefReaderTask().execute(intent);
    }
}

and adapt your AsyncTask accordingly:

private class NdefReaderTask extends AsyncTask<Intent, Void, String> {
    @Override
    protected String doInBackground(Intent... params) {
        Intent intent = params[0];
        Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
        byte[] uid = intent.getByteArrayExtra(NfcAdapter.EXTRA_ID);

        // ... //
    }

---

Some further refinements

1. There is no need for the fall-back intent filter TAG_DISCOVERED in your manifest. This will only trigger if no application on the device registered for more specific NFC events that match your tag. As your already registered for more specific event types (NDEF_DISCOVERED and TECH_DISCOVERED) this intent filter won't be used for your tags. So you can remove

   <intent-filter>
       <action android:name="android.nfc.action.TAG_DISCOVERED" />
       <category android:name="android.intent.category.DEFAULT"/>
   </intent-filter>
   

2. The TECH_DISCOVERED filter does not use any category, so you could also write:

   <intent-filter>
       <action android:name="android.nfc.action.TECH_DISCOVERED" />
   </intent-filter>
   

3. All MIFARE Ultralight tags are NFC-A tags, so using MifareUltralight + NfcA in the tech filter file is redundant. You could simply use

   <resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2">
       <tech-list>
           <tech>android.nfc.tech.Ndef</tech>
       </tech-list>
       <tech-list>
           <tech>android.nfc.tech.NfcA</tech>
       </tech-list>
   </resources>
   

4. Your foreground dispatch setup registers your activity to receive all NDEF_DISCOVERED events for data type "text/plain" and all TECH_DISCOVERED for tag technologies (MifareUltralight OR NfcA OR Ndef), and for all NFC discovery events (TAG_DISCOVERED). This is redundant and you yould also simply register for all NFC discovery events:

   public static void setupForegroundDispatch(final Activity activity, NfcAdapter adapter) {
       final Intent intent = new Intent(activity, activity.getClass());
       intent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);
   
       final PendingIntent pendingIntent = PendingIntent.getActivity(activity, 0, intent, 0);
   
       adapter.enableForegroundDispatch(activity, pendingIntent, null, null);
   }
   

5. When you simplify the foreground dispatch to trigger on any tag, Android will pass a TAG_DDISCOVERED intent to your app. So you have to update the handleIntent() method accordingly:

   private void handleIntent(Intent intent) { String action = intent.getAction();

       if (NfcAdapter.ACTION_TAG_DISCOVERED.equals(action) ||
           NfcAdapter.ACTION_TECH_DISCOVERED.equals(action) ||
           NfcAdapter.ACTION_NDEF_DISCOVERED.equals(action)) {
           new NdefReaderTask().execute(intent);
       }
   }
   

6. When your app should only detect tags while your activity is running in the foreground, you do not need any of the *_DISCOVERED filters in your app manifest.