Android NFC Reading a Tag

Question

In my application, I got two options : Writing and Reading a NFC tag. I am doing NFC Tag Writing process in another activity called WriteNFC. I want my main activity reads and displays tag data, when the tag comes into range. Writing process seem to be ok. But whenever i try to read the tag. It displays nothing.

public class MainActivity extends Activity {

public static int id = 1;
public static int bakiye = 5;
public static Context myContext;
public static boolean availableForRead = true;
private Button myButton;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    myButton = (Button) findViewById(R.id.button1);

    myButton.setOnClickListener(new View.OnClickListener() {

        public void onClick(View arg0) {

            Intent i = new Intent(getApplicationContext(), nfcWrite.class);
            startActivity(i);

        }
    });

}

@Override
protected void onResume() {
    // TODO Auto-generated method stub
    super.onResume();

}

@Override
protected void onNewIntent(Intent intent) {

    System.out.println("Intent detected");
    if (intent.getType() != null && intent.getType().equals("application/" + getPackageName())) {
        // Read the first record which contains the NFC data
        Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
        NdefRecord relayRecord = ((NdefMessage) rawMsgs[0]).getRecords()[0];
        String nfcData = new String(relayRecord.getPayload());
        System.out.println("Reading Process is Complete...");

        // Display the data on the tag
        Toast.makeText(this, nfcData, Toast.LENGTH_SHORT).show();

    }

}

}

And here is my nfcWrite activity:

package com.example.nfchandler;
import java.io.IOException;
import java.nio.charset.Charset;

import android.app.Activity;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.nfc.FormatException;
import android.nfc.NdefMessage;
import android.nfc.NdefRecord;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.nfc.TagLostException;
import android.nfc.tech.Ndef;
import android.nfc.tech.NdefFormatable;
import android.os.Bundle;
import android.widget.Toast;

public class nfcWrite extends Activity {

    private int id = 1;
    private int balance = 5;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.nfc_write);
    }

    @Override
    protected void onNewIntent(Intent intent) {
        // TODO Auto-generated method stub
        super.onNewIntent(intent);
         Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
            String nfcMessage = intent.getStringExtra("nfcMessage");

            if(nfcMessage != null) {
                writeTag(this, tag, nfcMessage);
            }
    }

    @Override
    protected void onResume() {
        // TODO Auto-generated method stub
        super.onResume();
        setupIntent();
    }

    public void setupIntent() {
        String nfcMessage = id + "-" + balance;

        // When an NFC tag comes into range, call the main activity which
        // handles writing the data to the tag
        NfcAdapter nfcAdapter = NfcAdapter.getDefaultAdapter(this);

        Intent nfcIntent = new Intent(this, nfcWrite.class).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);
        nfcIntent.putExtra("nfcMessage", nfcMessage);
        PendingIntent pi = PendingIntent.getActivity(this, 0, nfcIntent, PendingIntent.FLAG_UPDATE_CURRENT);
        IntentFilter tagDetected = new IntentFilter(NfcAdapter.ACTION_TAG_DISCOVERED);

        nfcAdapter.enableForegroundDispatch((Activity) this, pi, new IntentFilter[] { tagDetected }, null);
    }

    public boolean writeTag(Context context, Tag tag, String data) {
        // Record to launch Play Store if app is not installed
        NdefRecord appRecord = NdefRecord.createApplicationRecord(context.getPackageName());

        // Record with actual data we care about
        NdefRecord relayRecord = new NdefRecord(NdefRecord.TNF_MIME_MEDIA,
                new String("application/" + context.getPackageName()).getBytes(Charset.forName("US-ASCII")),
                null, data.getBytes());

        // Complete NDEF message with both records
        NdefMessage message = new NdefMessage(new NdefRecord[] { relayRecord, appRecord });

        try {
            // If the tag is already formatted, just write the message to it
            Ndef ndef = Ndef.get(tag);
            if (ndef != null) {
                ndef.connect();

                // Make sure the tag is writable
                if (!ndef.isWritable()) {
                    Toast.makeText(getApplicationContext(), "Etiket yazılabilir değil", Toast.LENGTH_SHORT).show();
                    return false;
                }

                // Check if there's enough space on the tag for the message
                int size = message.toByteArray().length;
                if (ndef.getMaxSize() < size) {
                    Toast.makeText(getApplicationContext(), "Etikette yeterli alan yok...", Toast.LENGTH_SHORT).show();
                    return false;
                }

                try {
                    // Write the data to the tag
                    ndef.writeNdefMessage(message);

                    Toast.makeText(getApplicationContext(), "Bilgileri yazma başarılı...", Toast.LENGTH_SHORT).show();

                    return true;
                } catch (TagLostException tle) {
                    return false;
                } catch (IOException ioe) {
                    return false;
                } catch (FormatException fe) {
                    return false;
                }
                // If the tag is not formatted, format it with the message
            } else {
                NdefFormatable format = NdefFormatable.get(tag);
                if (format != null) {
                    try {
                        format.connect();
                        format.format(message);

                        return true;
                    } catch (TagLostException tle) {
                        return false;
                    } catch (IOException ioe) {

                        return false;
                    } catch (FormatException fe) {

                        return false;
                    }
                } else {

                    return false;
                }
            }
        } catch (Exception e) {

        }

        return false;
    }

}

Answer 1

Following code solved my problem:

Intent intent=getIntent();

    NdefMessage[] msgs;
     if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(getIntent().getAction())) {
            Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
            NdefRecord relayRecord = ((NdefMessage)rawMsgs[0]).getRecords()[0];
            String nfcData = new String(relayRecord.getPayload());
            Toast.makeText(getApplicationContext(),nfcData,Toast.LENGTH_LONG).show();
        }

Answer 2

Your code has several issues regarding NFC functionality:

1. In your read activity you only check for NFC-related intents in the onNewIntent method. However, the onNewIntent method is only called under certain conditions. It is, for instance, not called upon initial start of your activity (e.g. due to being triggered by an intent filter in your manifest). In that case, you would need to process the received intent in either onCreate, onStart or onResume. Even if your activity is already visible when you scan a tag, onNewIntent will only fire if your activity is flagged as singleTop. For that case (when you want to be notified upon detection of tags while your activity is in the foreground, it is best to register for the NFC foreground dispatch.

2. In your write activity, you register for the NFC foreground dispatch system in the onResume method. However, you do not release the foreground dispatch in onPause. While this will work in the newest Android versions (4.4+?), this leads to sever problems on older Android versions.