Initialization of the Activity after it is first created. Must at least
call {@link android.app.Activity#setContentView setContentView()} to
describe what is to be displayed in the screen.
// Be sure to call the super class.
super.onCreate(savedInstanceState);
mSensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
mGraphView = new GraphView(this);
setContentView(mGraphView);