Android: Intent Filter for NDEF_DISCOVERED opens app in nfc window instead of running app

Question

I implemented this example: https://developer.android.com/guide/topics/connectivity/nfc/nfc#p2p

package com.example.android.beam;

import android.app.Activity;
import android.content.Intent;
import android.nfc.NdefMessage;
import android.nfc.NdefRecord;
import android.nfc.NfcAdapter;
import android.nfc.NfcAdapter.CreateNdefMessageCallback;
import android.nfc.NfcEvent;
import android.os.Bundle;
import android.os.Parcelable;
import android.widget.TextView;
import android.widget.Toast;
import java.nio.charset.Charset;


public class Beam extends Activity implements CreateNdefMessageCallback {
    NfcAdapter nfcAdapter;
    TextView textView;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        TextView textView = (TextView) findViewById(R.id.textView);
        // Check for available NFC Adapter
        nfcAdapter = NfcAdapter.getDefaultAdapter(this);
        if (nfcAdapter == null) {
            Toast.makeText(this, "NFC is not available", Toast.LENGTH_LONG).show();
            finish();
            return;
        }
        // Register callback
        nfcAdapter.setNdefPushMessageCallback(this, this);
    }

    @Override
    public NdefMessage createNdefMessage(NfcEvent event) {
        String text = ("Beam me up, Android!\n\n" +
                "Beam Time: " + System.currentTimeMillis());
        NdefMessage msg = new NdefMessage(
                new NdefRecord[] { createMime(
                        "application/vnd.com.example.android.beam", text.getBytes())
         /**
          * The Android Application Record (AAR) is commented out. When a device
          * receives a push with an AAR in it, the application specified in the AAR
          * is guaranteed to run. The AAR overrides the tag dispatch system.
          * You can add it back in to guarantee that this
          * activity starts when receiving a beamed message. For now, this code
          * uses the tag dispatch system.
          */
          //,NdefRecord.createApplicationRecord("com.example.android.beam")
        });
        return msg;
    }

    @Override
    public void onResume() {
        super.onResume();
        // Check to see that the Activity started due to an Android Beam
        if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(getIntent().getAction())) {
            processIntent(getIntent());
        }
    }

    @Override
    public void onNewIntent(Intent intent) {
        // onResume gets called after this to handle the intent
        setIntent(intent);
    }

    /**
     * Parses the NDEF Message from the intent and prints to the TextView
     */
    void processIntent(Intent intent) {
        textView = (TextView) findViewById(R.id.textView);
        Parcelable[] rawMsgs = intent.getParcelableArrayExtra(
                NfcAdapter.EXTRA_NDEF_MESSAGES);
        // only one message sent during the beam
        NdefMessage msg = (NdefMessage) rawMsgs[0];
        // record 0 contains the MIME type, record 1 is the AAR, if present
        textView.setText(new String(msg.getRecords()[0].getPayload()));
    }
}

in my app and added this intent-filter to the Manifest

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

When i now beam on one of the two devices, the intent executes the code in processIntent(), but inside of a program called NFC and not in my running app. So how can I get the Intent to execute in the running app and not to open the NFC application?

Andrew Andrew · Accepted Answer · 2021-01-16T20:08:27

You have non matching mime Types between the message you are creating which has mime Type of application/vnd.com.example.android.beam and the mime Type in the Manifest of text/plain you have asked the system to start you App if it sees.

Note that if you do match the mime Types, with this code it is likely depending on your App's launch mode to start you receiving App but for the App to not read the NFC message.

This is because onNewIntent is only called on Application re-launch and your application is not being re-launched.

Normal practise is the manifest filter starts you App with an Intent, you need to process this on App start (usually in onCreate).
onNewIntent is only used when your App is already running and has used enableForegroundDispatch to get the system to send NFC Intents to your running App instead of trying to start a new Instance of your App.

So in your code at the end of onCreate add the line

processIntent(getIntent());

Android: Intent Filter for NDEF_DISCOVERED opens app in nfc window instead of running app

1 Answers