loadLastViewport function

Implementation

Future<ViewportPosition?> loadLastViewport() async {
  try {
    final prefs = await SharedPreferences.getInstance();
    final lat = prefs.getDouble(keyLastLat);
    final lng = prefs.getDouble(keyLastLng);
    final zoom = prefs.getDouble(keyLastZoom);
    if (lat != null && lng != null && zoom != null) {
      return ViewportPosition(lat: lat, lng: lng, zoom: zoom);
    }
    return null;
  } catch (_) {
    return null;
  }
}