In my main activity I start a service. In that service, I try to get the sensor manager but I get the following exception

```
    Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference.

```

The error doesn't occur if I try to get the sensor manager in an activity class, it only happens in service class.

This is my main activity class:

```
    public class MainActivity extends AppCompatActivity
    {
        GridLayout mainGrid;

        @Override
        protected void onCreate(Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);

            Intent intent = new Intent(MainActivity.this, accelerometerBackgroundService.class);
            startService(intent);

            mainGrid = (GridLayout) findViewById(R.id.mainGrid);

            //Set Event
            setSingleEvent(mainGrid);
    //        setToggleEvent(mainGrid);
        }
    ...
     }

```

This is my service class:

```
    public class accelerometerBackgroundService extends Service implements SensorEventListener
    {
        //We need to log our activity to check what happens
        private static final String TAG = "Accelerometer_Activity";
        private SensorManager mSensorManager; //defining a sensor manager and the accelerometer
        private Sensor accelerometer;

        public accelerometerBackgroundService()
        {
            Log.i(TAG, "GOT HERE 100");
            //getting the sensor manager services
            mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);

            //getting the accelerometer sensor
            accelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
            if(accelerometer != null)
            {
                //If accelerometer sensor is available, create a listener
                mSensorManager.registerListener(this,mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER), SensorManager.SENSOR_DELAY_NORMAL);
            }
            else
            {
                String noAccelError = "This device does not support accelerometer sensor!";
            }
        }
        ...
        }

```

I imagine it has to do with the context. I've searched similar questions but didn't help me.

Thank you.