Zoom change event listener.

[macik1423]

Hi, I wonder is exist in flutter_map package v. 0.13.1 some zoom change event listener? I try change line width size according to zoom size. How can I handle this?

[vnmiso]

You can listen to map events and try to determine whether a zoom occurred there, until this functionality is implemened.
For example:

class MyMap extends StatelessWidget {
  // To be able to access the current zoom level at all times. Not strictly
  // needed, you can omit this.
  final _mapController = MapController();

  @override
  Widget build(BuildContext context) {
    return FlutterMap(
      options: MapOptions(onMapEvent: _handleMapEvent),
      mapController: _mapController,
    );
  }

  void _handleMapEvent(MapEvent event) {
    double? oldZoom;
    double? newZoom;

    // event.targetZoom should be the same as _mapController.zoom
    if (event is MapEventWithMove) {
      oldZoom = event.zoom;
      newZoom = event.targetZoom;
    } else if (event is MapEventDoubleTapZoom) {
      oldZoom = event.zoom;
      newZoom = event.targetZoom;
    }
    // There is a case that I was not able to handle: you can zoom by double
    // tapping and then dragging, but no events seem to be generated, so this
    // code doesn't detect that.
    // Other checks you might consider instead of the ones above:
    //   event.source == MapEventSource.scrollWheel
    //   event.source == MapEventSource.doubleTapZoomAnimationController

    // Check whether a zoom event occurred and whether you want to handle it.
    if (oldZoom != null && newZoom != null && oldZoom != newZoom) {
      // ...
    }
  }
}

You can also attach the map event handler to a MapController's mapEventStream if you're using that.