Working with map objects

During the class, we did operations with objects in the map. We have created MarkerManager. A class to help us manage markers in the map. It has a HashMap, which holds all the markers in the map. It is useful to hold the references for later use, like removing them.

Part of the MarkerManager is also a method for creating a custom marker icon from a layout file.

Once you create a marker, you can add a tag to it. The tag is very useful for holding the information about what is the object that marker represents.

class MarkerManager {

    private val markers: HashMap<Long, Marker> = hashMapOf()

    fun addMarkerToMap(context: Activity,
                       map: GoogleMap, place: Place ) {
        if (!markers.containsKey(place.id)){
            // the map of markers does not contain the marker with this id
            val options = MarkerOptions()
            options.position(LatLng(place.latitude, place.longitude))
            options.icon(BitmapDescriptorFactory.fromBitmap(createCustomMarkerBitmap(context, place.id!!)))
            options.draggable(true)
            val marker = map.addMarker(options)
            marker.tag = place.id
            markers.put(place.id!!, marker)
        }
    }

    fun removeMarker(id:Long) {
        if (markers.containsKey(id)){
            val marker = markers.get(id)
            marker?.remove()
            markers.remove(id)
        }
    }

    private fun createCustomMarkerBitmap(context: Activity, id: Long): Bitmap {
        val markerView = LayoutInflater.from(context).inflate(R.layout.marker_layout, null)
        val textView = markerView.findViewById<TextView>(R.id.markerIdTV)
        textView.text = id.toString()
        val displayMetrics = DisplayMetrics()
        context.windowManager.defaultDisplay.getMetrics(displayMetrics)
        markerView.measure(displayMetrics.widthPixels, displayMetrics.heightPixels)
        markerView.layout(0, 0, displayMetrics.widthPixels, displayMetrics.heightPixels)
        markerView.buildDrawingCache()
        val bitmap = Bitmap.createBitmap(
            markerView.getMeasuredWidth(),
            markerView.getMeasuredHeight(),
            Bitmap.Config.ARGB_8888
        )
        val canvas = Canvas(bitmap)
        markerView.draw(canvas)
        return bitmap
    }
}

Another part of working with map is controlling the map virtual camera. We have also created a class for it.

class MapManager {

    fun zoomToLocation(location: LatLng, googleMap: GoogleMap){
        googleMap.animateCamera(
            CameraUpdateFactory.newLatLngZoom(location, 7.0f))
    }

    fun zoomToAllPlaces(googleMap: GoogleMap, places: MutableList<Place>){
        if (places.size > 0) {
            val builder = LatLngBounds.Builder()
            for (place in places) {
                builder.include(LatLng(place.latitude, place.longitude))
            }
            googleMap.animateCamera(
                CameraUpdateFactory.newLatLngBounds(builder.build(), 100)
            )
        }
    }
}

The class has two methods. One is for zooming to a specified location. The zoom level is between 2 and 21.

The second method is for zooming to all places using the LatLngBounds class.

Honourable mentions during the class:

• MaterialCardView — class for creating a card like design element. Very useful.
• lateinit — a keyword in kotlin the specify, that we will initialize the class later in code.
• ConstrainedLayout — very useful layout for holding other elements.
• moveCamera — a method of google map to just move the camera.
• animateCamera — a method of google map to animate the change of camera position. Looks better than move.