Adding markers dynamically to flutter google map

Question

I'm using Flutter to make a mobile application that uses a map. We decided to use Google map and the plugin for flutter we use is:

google_maps_flutter: ^0.5.7

I understand that adding markers to the map works like this:

Map<MarkerId, Marker> markers = <MarkerId, Marker>{};
Marker _marker = new Marker(
  icon: BitmapDescriptor.defaultMarker,
  markerId: _markerId,
  position: LatLng(34.024441,-5.0310968),
  infoWindow: InfoWindow(title: "userMarker", snippet: '*'),
);
GoogleMap _map;

@override
void initState(
   markers[_markerId] = _marker;
   _map = new GoogleMap(
    /* other properties irrelevant to this prob */
    markers: Set<Marker>.of(_markers.values),
  );
);

The above snippet does work, I get to see the marker on the map. But modifying the marker or trying to add another marker like in the snippet below does not work.

FloatingActionButton(
    onPressed: () {
      setState(() {
        _marker = new Marker(
            icon: BitmapDescriptor.defaultMarker,
            markerId: _markerId,
            position: LatLng(currentLocation.latitude, currentLocation.longitude),
            infoWindow: InfoWindow(title: "userMarker", snippet: '*'),
            onTap: () {
              debugPrint("Marker Tapped");
            },
          );
        markers[_markerId] = _marker; // What I do here is modify the only marker in the Map.
      });
      markers.forEach((id,marker) { // This is used to see if the marker properties did change, and they did.
        debugPrint("MarkerId: $id");
        debugPrint("Marker: [${marker.position.latitude},${marker.position.longitude}]");
      });
    });
)

My intention here is using another plugin (geoLocator) to get location data of the user and change the only marker I have so it can track his movements. The debugPrint shows that the data is indeed changing, but I see no change in the map (the initial marker that I change uses a different location than my own when I test).

Answer 1

If there's no specific reason for you to use Map data structure, here's what I've done in the past.

I have a Set of Marker in my State

Set<Marker> markers = Set();

Give it to the map widget. markers: markers

GoogleMap(
  onMapCreated: _onMapCreated,
  myLocationEnabled: true,
  initialCameraPosition:
    CameraPosition(target: LatLng(0.0, 0.0)),
  markers: markers,
)

And then adding the Marker, which I'm building with search result and which you'll be building with your user's location, to Set of Marker in setState method.

// Create a new marker
Marker resultMarker = Marker(
  markerId: MarkerId(responseResult.name),
  infoWindow: InfoWindow(
  title: "${responseResult.name}",
  snippet: "${responseResult.types?.first}"),
  position: LatLng(responseResult.geometry.location.lat,
  responseResult.geometry.location.lng),
);
// Add it to Set
markers.add(resultMarker);

Edit: I've just noticed you're using GoogleMap widget in your initState, you need to move it to the build method if you want to rebuild it everytime with the new state values.