I`m working on an app that does reading and handling specific URIs from NFC

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Asked: May 28, 20262026-05-28T02:06:23+00:00 2026-05-28T02:06:23+00:00

I`m working on an app that does reading and handling specific URIs from NFC

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I`m working on an app that does reading and handling specific URIs from NFC tags. I have a “reader” activity (A) registered on NDEF_DISCOVERED which reads the data from the tag and than launches a “data handling” activity (B) that operates with the data.

Currently I have three tags, each with a different URI, more specifically with the same schema and path, but with different query data –> the tagID:

T-1: mySchema://gman.com/path?id=T-1
T-2: mySchema://gman.com/path?id=T-2
T-3: mySchema://gman.com/path?id=T-3

Manifest:

   <activity
        android:label="@string/reader_nfc"
        android:name=".reader.nfc.NfcReaderActivity"
        android:stateNotNeeded="true" >
        <intent-filter>
            <action android:name="android.nfc.action.NDEF_DISCOVERED" />
            <category android:name="android.intent.category.DEFAULT" />
            <data android:scheme="mySchema" />
        </intent-filter>
    </activity>
    <activity
        android:label="@string/data_manager_name"
        android:name=".data.handlers.DataHandlerActivity" >
    </activity>

So, getting to the problem. When I read the data from the first tag, for example T-1, the reader activity goes normally trough the lifecycle and launches the data handling activity which does its job and shows the correct output. The same thing happens when I read from the next tag (T-2 or T-3), but when I return to the first tag I get the output produced from the last-previously scanned tag.

The log shows something like this:

the ActivityManager logs the the start of the intent with the right data (from T-1) but the lifecycle of activity A doesn`t get started, instead activity B restarts and the data from the previous intent is received and handled (by calling getIntent().getData() in activity B).

When switching between T-2 and T-3 everything works fine.

I would really appreciate if someone explaind me what is going on. I saw similar behaviour when setting singleTask launch mode, but I`m not using it.

I`m developing on API v.2.3.3, testing on Nexus-S with android version 2.3.6

Thnx!

==================================================================================

EDIT: I found a solution on my problem which fits my needs, still I have a question.

I focused on the reader activity and commented out the handling and the other stuff that was going on. Here is the code snipet:

public class NfcReaderActivity extends Activity {

private static final String TAG = "NfcReaderActivity";

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Log.d(TAG, "onCreate");
    setContentView(R.layout.nfc_reader);
}

@Override
protected void onStart() {
    super.onStart();
    Log.d(TAG, "onStart");

    readAndHandleData();
}

protected void readAndHandleData() {
    NdefMessage[] srcObj = readSource();

    if (srcObj != null) {
        Uri srcData = getSrcData(srcObj);
        launchSourceManagerActivity(srcData);
    } else {
        Log.w(TAG, "srcObj was null!");
    }
}

public NdefMessage[] readSource() {

    Parcelable[] rawMsgs = getIntent().getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
    NdefMessage[] ndefMsgs = null;
    // store NdefMessage-s from rawMsgs in ndefMsgs
    return ndefMsgs ;
}

public void launchSourceManagerActivity(Uri srcData) {
    // launches DataHandlerActivity with srcData
}

public Uri getSrcData(NdefMessage[] src) {
    // returns the data from the tag rapresented as Uri
}

}

After doing this I got some extra logs (don’t know why, but I guess this is not that important), and saw that when I’m returning to the first tag, the activity gets restarted (onRestart() is called), whereas in the other two cases, when scanning the second and the third tag, the activity is recreated (onCreate() is called).

When onRestart() is called and I retrieve the data from the intent (readSource method), the getIntent() method returns the same intent received when scanning the previous tag.

I just recently started developing on Android and I`m not very familiar with the concepts, so maybe this is the core problem here ;). I tried to figure this out but I just can’t get to a logical explanation. If someone could explain me the workflow here I would be really grateful.

However, this is how I resolved the issue…since the reader activity can act as a singleton I’ve set the launch mode as singleTask

<activity
        android:label="@string/reader_nfc"
        android:name=".reader.nfc.NfcReaderActivity"
        android:stateNotNeeded="true"
        android:launchMode="singleTask"  >

and done the following changes in NfcReaderActivity:

public class NfcReaderActivity extends Activity {

private static final String TAG = "NfcReaderActivity";

/**
 * override onNewIntent method and store the new intent as the current intent
 */
@Override
protected void onNewIntent(Intent intent) {
    super.onNewIntent(intent);
    Log.d(TAG, "onNewIntent");
    // set the intent as the current intent, so new data (EXTRA_NDEF_MESSAGES) can
 //be accessed when calling getIntent() in readSource method
    setIntent(intent);
}

This works fine for me, but I would still like to understand what exactly was happening, so any useful (of course 😉 ) comments are welcome.