如何在不同的活动中读写NFC卡

Question

I have two activities. I want to use the first activity (as MainAcitivity ) to read cards, and the second activity to write cards. Because the activity needs to be active when the card is discovered. Thus, I used the below setting for both activities:

        </intent-filter>
        <!-- Handle notes detected from outside our application -->
        <intent-filter>
            <action android:name="android.nfc.action.NDEF_DISCOVERED" />
            <category android:name="android.intent.category.DEFAULT" />
            <data android:mimeType="text/plain" />
        </intent-filter>

However, my problem is that when I am in the second activity and I scan an NFC card, the phone will show an intent chooser for both, the first and the second activity.

So, how can I disable the NDEF_DISCOVERED intent filter of the first activity while I am in the second activity (and the other way round) by code?

This is the full AndroidManifest file:

   <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".FirstActivity"
            android:label="@string/app_name"
            android:configChanges="orientation|screenSize|screenLayout"
             >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
            <!-- Handle notes detected from outside our application -->
            <intent-filter>
                <action android:name="android.nfc.action.NDEF_DISCOVERED" />
                <category android:name="android.intent.category.DEFAULT" />
                <data android:mimeType="text/plain" />
            </intent-filter>
        </activity>
        <activity 
            android:name=".SecondActivity"
            android:label="@string/app_name">
           <intent-filter>
                <action android:name="android.nfc.action.NDEF_DISCOVERED" />
                <category android:name="android.intent.category.DEFAULT" />
                <data android:mimeType="text/plain" />
            </intent-filter>
        </activity>
    </application>

Answer 1

In order to force NFC discovery events to be received by the activity that is currently in the foreground, you could use either the foreground dispatch system or the reader-mode API .

Both of these methods will give an activity precedence in receiving NFC discovery events if it is currently in the foreground.

So you could, for instance, use something like:

public void onResume() {
    super.onResume();
    NfcAdapter nfcAdapter = NfcAdapter.getDefaultAdapter(this);
    PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);

    // to catch all NFC discovery events:
    nfcAdapter.enableForegroundDispatch(this, pendingIntent, null, null);

    // or to only catch text/plain NDEF records (as you currently do in your manifest):
    //IntentFilter ndef = new IntentFilter(NfcAdapter.ACTION_NDEF_DISCOVERED);
    //try {
    //    ndef.addDataType("text/plain");
    //} catch (MalformedMimeTypeException e) {}
    //nfcAdapter.enableForegroundDispatch(this, pendingIntent, new IntentFilter[] { ndef }, null);
}

public void onPause() {
    super.onPause();
    NfcAdapter nfcAdapter = NfcAdapter.getDefaultAdapter(this);
    nfcAdapter.disableForegroundDispatch(this);
}

public void onNewIntent(Intent intent) {
    if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(intent.getAction()) ||
        NfcAdapter.ACTION_TECH_DISCOVERED.equals(intent.getAction()) ||
        NfcAdapter.ACTION_TAG_DISCOVERED.equals(intent.getAction())) {
        // handle NFC events ...
    }
}

Moreover, if you do not want an activity to be started by NFC discovery events, you do not need to declare an android.nfc.action.*_DISCOVERED intent filter in the mainfest for that activity.