NFC tag detection is not calling onNewIntent and it’s Launching From Main Activity

NFC Tag Detection Issues: onNewIntent Not Called, Launching From Main Activity

This article addresses a common issue encountered when working with NFC tag detection in Android applications: the `onNewIntent` method not being called when a tag is detected, resulting in the app launching from the main activity instead of handling the tag directly.

Understanding the Problem

In Android, when an NFC tag is detected, the app should ideally receive the tag data through the `onNewIntent` method within the activity responsible for handling NFC interactions. However, sometimes the app instead launches from the main activity, bypassing the intended NFC handling activity.

Potential Causes

• Missing `android:launchMode=”singleTop”` in Manifest: The `android:launchMode` attribute in the AndroidManifest.xml file determines how an activity is launched. If the activity handling NFC is not set to `singleTop`, a new instance of the activity will be created upon each tag detection, overriding the previous instance and preventing `onNewIntent` from being called.
• Incorrect Intent Filters: The activity responsible for NFC handling requires specific intent filters in the Manifest to properly receive and interpret NFC events. If the filters are incomplete or incorrect, the system may not recognize the activity as a suitable handler, leading to the app launching from the main activity.
• NFC Permissions: Ensuring the app has the necessary NFC permissions (READ_NFC and WRITE_NFC) is crucial for proper tag detection and handling. Missing permissions can cause unexpected behavior, including the failure to call `onNewIntent`.
• Background Processing: If the app is running in the background, it may not be able to immediately process the tag detection event. This can lead to the app launching from the main activity when brought to the foreground.

Troubleshooting and Solutions

1. Manifest Configuration

Ensure the activity handling NFC has the `singleTop` launch mode set in the AndroidManifest.xml:

<activity
    android:name=".NFCActivity"
    android:exported="true"
    android:launchMode="singleTop">
    ...
</activity>

2. Intent Filters

Define the correct intent filters for the NFC handling activity in the Manifest:

<activity
    android:name=".NFCActivity"
    ...>

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

</activity>

3. Permissions

Declare NFC permissions in the Manifest:

<uses-permission android:name="android.permission.READ_NFC" />
<uses-permission android:name="android.permission.WRITE_NFC" />

4. Foreground Activity

Ensure the app is in the foreground when a tag is detected. Consider using foreground services to handle NFC events in the background.

5. Debug and Test

Utilize logging and debugging tools to track the app’s flow when a tag is detected. Examine the logcat output for relevant error messages or unexpected behavior.

Code Example

Here is a basic example of how to handle NFC tag detection using `onNewIntent`:

package com.example.nfc;

import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.os.Bundle;
import android.util.Log;

public class NFCActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_nfc);

        NfcAdapter adapter = NfcAdapter.getDefaultAdapter(this);
        if (adapter != null && adapter.isEnabled()) {
            // Enable foreground dispatch
            adapter.enableForegroundDispatch(this, getIntent(), new IntentFilter[]{
                    new IntentFilter(NfcAdapter.ACTION_TECH_DISCOVERED)
            }, null);
        } else {
            // NFC not available or disabled
            Log.e("NFC", "NFC not available or disabled");
        }
    }

    @Override
    protected void onNewIntent(Intent intent) {
        super.onNewIntent(intent);

        // Check for NFC tag event
        if (intent.getAction().equals(NfcAdapter.ACTION_TECH_DISCOVERED)) {
            Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
            // Process the tag data
            Log.d("NFC", "Tag detected: " + tag.toString());
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        NfcAdapter adapter = NfcAdapter.getDefaultAdapter(this);
        if (adapter != null) {
            // Disable foreground dispatch
            adapter.disableForegroundDispatch(this);
        }
    }
}

D/NFC: Tag detected: NfcA: [uid=04010300000000000000000000000000 techList=[android.nfc.tech.NfcA, android.nfc.tech.Ndef, android.nfc.tech.NdefFormatable]]

Conclusion

By addressing potential issues related to manifest configuration, intent filters, permissions, and background processing, you can ensure that your app correctly handles NFC tag detection and invokes the `onNewIntent` method, allowing you to process tag data directly in the intended activity. Remember to test and debug your implementation thoroughly to catch any unexpected behavior.