marker_manager.dart

  List<SingleChildWidget> providerItems = [ Provider.value(value: CustomMarkerManager())}]
 
class CustomMarkerManager extends CustomMarker {
  Map<int, BitmapDescriptor> _markers = {};

  Future<BitmapDescriptor> getCustomMarker({
    int value,
    Color clusterColor,
    Color textColor,
    int width,
  }) async {
    final marker = _markers[value];
    if (marker != null) {
      return marker;
    } else {
      final newMarker =
          await CustomMarker(clusterColor: clusterColor, width: width, textColor: textColor, clusterSize: value)
              .getCustomMarker();
      _markers[value] = newMarker;
      return newMarker;
    }
  }