Android - Listening to NFC Adapter State Changed

问题:

I am trying to build an application which uses NFC. The goal is to display a DialogFragment containing a button link to go the settings and change it manually and when the feature is enabled, disable the DialogFragment.

Problem: If the user enables/disables NFC using the icon in the pull down notifications tray , then the onPause/onResume doesn't get called and misses the condition entirely. I am sure there is a receiver that I can register to instead and respond appropriately in real time. Any ideas, thoughts or reference will be greatly appreciated!

The following code checks if the state is enabled/disabled. I am also responding to it appropriately in the onResume event.

    NfcManager manager = (NfcManager) getSystemService(Context.NFC_SERVICE);     NfcAdapter adapter = manager.getDefaultAdapter();      if(adapter != null && adapter.isEnabled()) {         detector = new NfcDetector(this);         detector.setListener(this);         onNfcFeatureFound();     }     else {         onNfcFeatureNotFound();     }

For others looking at this post, the code below will take the user directly into settings to enable/disable NFC:

startActivity(new Intent(android.provider.Settings.ACTION_NFC_SETTINGS));

回答1:

Thought I should post the answer for other people looking for the same problem, since I wasn't able to find one easily.

Add the following code to your activities onCreate() method:

IntentFilter filter = new IntentFilter(NfcAdapter.ACTION_ADAPTER_STATE_CHANGED); this.registerReceiver(mReceiver, filter);

Inner private class declared within your activity (or anywhere else you like):

private final BroadcastReceiver mReceiver = new BroadcastReceiver() {     @Override     public void onReceive(Context context, Intent intent) {         final String action = intent.getAction();          if (action.equals(NfcAdapter.ACTION_ADAPTER_STATE_CHANGED)) {             final int state = intent.getIntExtra(NfcAdapter.EXTRA_ADAPTER_STATE,                                                  NfcAdapter.STATE_OFF);             switch (state) {             case NfcAdapter.STATE_OFF:                 break;             case NfcAdapter.STATE_TURNING_OFF:                 break;             case NfcAdapter.STATE_ON:                 break;             case NfcAdapter.STATE_TURNING_ON:                 break;             }         }     } };  @Override public void onDestroy() {     super.onDestroy();      // Remove the broadcast listener     this.unregisterReceiver(mReceiver); }    // The following check needs to also be added to the onResume @Override protected void onResume()      super.onResume();   // Check for available NFC Adapter     PackageManager pm = getPackageManager();     NfcManager manager = (NfcManager) getSystemService(Context.NFC_SERVICE);     NfcAdapter adapter = manager.getDefaultAdapter();      if(adapter != null && adapter.isEnabled()) {         createNfcDetector();         onNfcFeatureFound();     }     else {         onNfcFeatureNotFound();     } }

回答2:

You can use ACTION_ADAPTER_STATE_CHANGED to receive a broadcast message when the state of the adapter changes, but that option is only available in API 18 and above. See this for the documentation.

For prior to 18, I don't know of a way to do this unfortunately.

Also, as an aside, the android.provider.Settings.ACTION_NFC_SETTINGS will work on API levels 16 and above. For prior versions, the NFC settings are under "wireless settings". Take a look at the ensureSensorIsOn method at the bottom of this blog post for a code sample that checks against the API level and redirects to the correct settings pane.

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