@Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    mContext = this;
    setContentView(R.layout.activity_map);

    // Obtain the SupportMapFragment and get notified when the map is ready to be used.
    SupportMapFragment mapFragment =
        (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
    mapFragment.getMapAsync(this);
  }
  @Override
  protected void onDestroy() {
    if (!bitmap_mapping.isEmpty()) {
      for (int key : bitmap_mapping.keySet()) {
        Bitmap bm = bitmap_mapping.get(key);
        if (bm != null && !bm.isRecycled()) {
          bm.recycle();
          bm = null;
        }
      }
    }
    bitmap_mapping = null;

    super.onDestroy();
  }