Receiver class doesn't recognize ACTION_BATTERY_CHANGED

Question

I want to play a sound as a notification when battery charge is full.

in my receiver class I wrote 2 more notifications for "power connected" and "power disconnected" and they works ok!

but my receiver doesn't recognize the ACTION_BATTERY_CHANGED. I've searched a lot and I found out that I must register it programmatically.

The problem is that I need to register it without any Activity. Because I want to notify "Battery_Fully_charged" even when my program doesn't run.

how can I register something like this within my receiver ("MyReceiver.class")?

here is the sample code that I found and it workes. But I want to do it without an Activity.

public class Main extends Activity {
  private TextView batteryTxt;
  private BroadcastReceiver mBatInfoReceiver = new BroadcastReceiver(){
    @Override
    public void onReceive(Context ctxt, Intent intent) {
      int level = intent.getIntExtra(BatteryManager.EXTRA_LEVEL, 0);
      batteryTxt.setText(String.valueOf(level) + "%");
    }
  };

  @Override
  public void onCreate(Bundle b) {
    super.onCreate(b);
    setContentView(R.layout.main);
    batteryTxt = (TextView) this.findViewById(R.id.batteryTxt);
    this.registerReceiver(this.mBatInfoReceiver, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
  }
}

Edit: what is the difference between Service and Broadcase Receiver? I tried the Service but still didn't get any result

Answer 1

From documentation:

You cannot receive this through components declared in manifests, only by explicitly registering for it with Context.registerReceiver(). [...]

This means:

1) Only a BroadcastReceiver can receive these intents.

2) Only a dynamically registered receiver can receive these intents.

You already understand how to do it inside an activity let's look at the service:

public class MyService extends Service {

    private final IntentFilter batteryIntentFilter = new IntentFilter(Intent.ACTION_BATTERY_CHANGED);
    private final BroadcastReceiver batteryReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context ctxt, Intent intent) {
            // React.
        }
    };

    public void onCreate() {
        super.onCreate();
        registerReceiver(batteryReceiver, batteryIntentFilter);
    }

    public void onDestroy() {
        unregisterReceiver(batteryReceiver);
        super.onDestroy();
    }

    public int onStartCommand (Intent intent, int flags, int startId) {
        return START_STICKY;
    }
}

You can decrease the chance of the service getting killed by putting it to foreground (google "foreground service").

As mentioned in http://developer.android.com/preview/behavior-changes.html#bg-opt some implicit intents are going away so be prepared ACTION_BATTERY_CHANGED is going to be among them.