How to use Firebase EventListener as a background service in android?

Question

I am trying to make a background service that runs even if the application is closed. this services is supposed to listen to Firebase changes, and start the application according to a trigger. I don't know whether I am missing something in the code or not even close to the right answer, but here is my code :

public class FireBaseService extends Service {

private HashMap<String, String> fireBaseBattery;

@Override
public void onCreate() {
    super.onCreate();

    fireBaseBattery = new HashMap<>();
    final Firebase firebaseRef_Battery = new Firebase("the url i want to take data from");

    firebaseRef_Battery.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if (dataSnapshot.getValue() != null) {
                fireBaseBattery = (HashMap<String, String>) dataSnapshot.getValue();
                String battery = (String) fireBaseBattery.get("battery");
                int battery_int = Integer.parseInt(battery);

                System.out.println("SERVICE FIREBASE : " + battery);
                if (battery_int <= 10) {
                    Intent intent = new Intent(getApplicationContext(), MainActivity.class);
                    startActivity(intent);
                }
            }
        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {

        }
    });
}

@Nullable
@Override
public IBinder onBind(Intent intent) {
    return null;
}

}

And this is the manifest :

    <uses-permission android:name="android.permission.READ_SMS" />
    <application
        android:name=".ParseApplication"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

<service android:enabled="true"
        android:name=".FireBaseService">
    </service>
        <activity
            android:name=".Launcher"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
 </application>

</manifest>

Edit : I added a line in MainActivity.class to start the service

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    startService(new Intent(this, FireBaseService.class));
}

Answer 1

I edited the Application as following :

1. The Service class extends Activity and not Service
2. I added the service manifest inside the application tag directly as the following :

android:name=".FireBaseService"

3. There is no need to start the service from main activity.

Edited Manifest:

 <uses-permission android:name="android.permission.READ_SMS" />
<application
    android:name=".FireBaseService"
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">

    <activity
        android:name=".Launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme.NoActionBar">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>