Google Maps user-editable polygon with fixed number of points in Android?

Question

I am working on Google Map polygon marker, I have predefined lat/long array, and need to set polygon area, It is working fine for me, but when I drag the marker polygon line doesn't change, it should have to be change as I drag the marker.

Here is my problem, I'll put a picture to illustrate it easier.

here is the code:

    myMap.setOnMarkerDragListener(new GoogleMap.OnMarkerDragListener() {
        @Override
        public void onMarkerDragStart(Marker marker) {
        }

        @Override
        public void onMarkerDrag(Marker marker) {
            updateMarkerLocation(marker);
            drawPolygon(coordinates);

        }

        private void updateMarkerLocation(Marker marker) {

            LatLng latLng = (LatLng) marker.getTag();
            int position = coordinates.indexOf(latLng);
            if (position >= 0) {
                coordinates.set(position, marker.getPosition());
                marker.setTag(marker.getPosition());
            }
        }

        @Override
        public void onMarkerDragEnd(Marker marker) {

        }
    });
}

private void drawPolygon(List<LatLng> coordinates) {

    if (polygon != null) {
        polygon.remove();
    }

    PolygonOptions polygonOptions = new PolygonOptions();
    polygonOptions.fillColor(Color.GREEN);
    polygonOptions.strokeColor(Color.GREEN);
    polygonOptions.strokeWidth(3);
    polygonOptions.addAll(coordinates);
    polygon = myMap.addPolygon(polygonOptions);

}

like above image my marker move but not make polygon.

coordinates contain polygon coordinates from sqlite

Answer 1

It looks like you're using the Marker tag to store the last displayed coordinate ( LatLng ) of the polygon point. The coordinates to be displayed are stored in coordinates yes?

If so then I'm guessing your code should be:

private void updateMarkerLocation(Marker marker) {
  LatLng latLng = (LatLng) marker.getTag();
  int position = coordinates.indexOf(latLng);
  if (position >= 0) {
    coordinates.set(position, marker.getPosition());
    marker.setTag(marker.getPosition());
  }
}

Answer 2

I think you're using the tools you have a little inefficiently. My recommendation would be to store an array of markers, and use markerTag to store the index of your point, so in drawPolygon

for (int i = 0; i < coordinates.size(); i++) {
   markers[i].setTag(i); //Associate a marker with a point
}

Then, when you move the marker, you would replace the co-ordinate at that point like so:

points[marker.getTag().toInt()] = marker.getTag().getPosition();

Sorry this is so vague. I use kotlin, so I've probably gotten some of the syntax wrong, too.