Android NFC Intents are not starting my activity

问题:

I am trying to write a simple application to interact with NFC tags, but I cant seem to get my phone to do anything but trigger the default NFC tag app. I really just want to be able to intercept any tag I scan, determine if it has some data on it, and take action accordingly.

Right now my manifest file looks like

<uses-sdk android:minSdkVersion="10" />
<uses-feature android:name="android.hardware.nfc" android:required="true"/>
<uses-permission android:name="android.permission.NFC"/>

<application 
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name" >
    <activity
        android:name=".NfcActivity"
        android:label="@string/app_name">
        <intent-filter>
           <action android:name="android.intent.action.MAIN"/>
           <category android:name="android.intent.category.LAUNCHER"/>
        </intent-filter>
        <intent-filter>
            <action android:name="android.nfc.action.NDEF_DISCOVERED"/>
        </intent-filter>
    </activity>
</application>

However when scanning an NFC tag, I never see the activity start. Am I missing something here? I tried placing the intent filter inside a BroadcastReceiver and had no luck either...

回答1:

You cannot have your app started by all NFC tags you scan. Android will determine what the most suitable app is based on how specific the intent filter is. However, if your app is running in the foreground, you can use NFC foreground dispatch to catch all NFC intents.

In onCreate() add:

mAdapter = NfcAdapter.getDefaultAdapter(this);
PendingIntent pendingIntent = PendingIntent.getActivity(
  this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);

In onResume() add:

mAdapter.enableForegroundDispatch(this, pendingIntent, null, null);

In onPause() add:

mAdapter.disableForegroundDispatch(this);

In onNewIntent you can get at the NFC tag like this:

Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);

回答2:

The SDK docs show this as a basic example.

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

回答3:

You are expecting the tags to be defined in NDEF format. So your program will only be launched if the tags being read is in NDEF format.

You can try more generic intent filters like TAG_DISCOVERED or TECH_DISCOVERED.

回答4:

Android automatically choses the most relevant application to handle the scanned NFC tag. You need to be more specific in your intent-filter, i.e. only listen for TEXT-Tags, URL-Tags, or CONTACT-Tags. This can be done by further specifying the filter, using, your example, <data android:mimeType="text/plain" /> for TEXT-Tags. Otherwise, the default NFC-Tag app will be triggered.