Handle fast add/remove Marker commands / Google Maps v2+ScrollListener

Question

I want to perform fast add/remove or hide/show markers based on a list (the range between firstVisibleItem and lastVisibleItemsPrevious.

This is a list that assign from my database on a temporarily on

private List<MarkerOptions> mMarkers = new ArrayList<MarkerOptions>();
private int firstVisibleItemPrevious = 0;
private int lastVisibleItemsPrevious = 0;

//Loops, network commands, etc
// assign a marker per item
    MarkerOptions markerOptions = new MarkerOptions()
                .icon(BitmapDescriptorFactory.fromResource(R.drawable.marker))
                .anchor(0.5f, 0.5f)
                .visible(false)
                .position(new LatLng( (Double) coords.get(1) , (Double) coords.get(0)));            

    mMarkers.add(position, markerOptions);

And this is how the I/O of the markers is done:

aListView.setOnScrollListener(new OnScrollListener() {
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
        int lastVisibleItem = firstVisibleItem+visibleItemCount;

        //if we have the markers from the DB and we notice a move do:
        if( mMarkers.size() > 0 && 
                (firstVisibleItemPrevious != firstVisibleItem ||
                lastVisibleItemsPrevious != lastVisibleItem)
                ){

            LatLngBounds.Builder builder = new LatLngBounds.Builder();
            mMap.clear(); // clear the map to add new markers

            for(int x = firstVisibleItem; x < lastVisibleItem; x++){                    
                Marker mMarker = mMap.addMarker(mMarkers.get(x));
                builder.include(mMarker.getPosition());
            }

            //animate
            CameraUpdate cu = CameraUpdateFactory.newLatLngBounds(builder.build(), 60);
            mMap.animateCamera(cu);

            firstVisibleItemPrevious = firstVisibleItem;
            lastVisibleItemsPrevious = lastVisibleItem;
        }
    }
}

With my method I have three problems:

• The first is that I wipe completely the map (blink).
• Some markers are not always assigned correctly (I cannot understand why).
• Therefore the animateCamera looks like it has not correctly all positions of the builder

I tried a method of checking the current visible maps (a list) and check the new list and then add those that are not in the old list and remove those that are not in the new list. However it was still laggy and I ended up adding always markers and not correctly remove the "old" ones. I also tried with Marker.setVisibility() without success.

What can be a good way to handle these kind of fast operations? Keeping in mind that I should at least have a list of List<MarkerOptions> or List<LatLng> or List<Marker> as my source for the hide/show operation (assigned dynamically).

Answer 1

The bug was in the

mMarkers.add(position, markerOptions);

It was pushing the list.