Android Google Maps - how to check if Polyline is null

Question

I am trying to check if my polyline variable contains any assigned polylineoptions.

When the activity loads, the onMapReady method is automatically called and thus I get a compiler error when I try to set the points of a polyline to null (see code below)

Assignment of data to a polyline looks something like this:

    mMap = googleMap;
    double[] firstCoords;
    double[] lastCoords;
    double[] receivedDataArray;
    double latitude;
    double longitude;

    ArrayList<LatLng> coordList = new ArrayList<LatLng>();
    coordList.clear();


    polyline.setPoints(null); //ERROR HERE


    for (int i = 0; i < coordinatesArray.size() - 1; i++) {
        receivedDataArray = coordinatesArray.get(i);

        latitude = receivedDataArray[0];
        longitude = receivedDataArray[1];

        coordList.add(new LatLng(latitude,longitude));
    }

    options = new PolylineOptions().addAll(coordList).width(10).color(Color.BLUE).geodesic(true);
    polyline = mMap.addPolyline(options);

I attempted to do a check to see if the polyline contains any data but I get compiler errors as well on both of these checks:

if(polyline.getOptions() != null){
   polyline.setPoints(null); 
}

or

if(!polyline.getOptions().isEmpty()) {
   polyline.setPoints(null); 
}

error when checking for null:

java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.List com.google.android.gms.maps.model.Polyline.getPoints()' on a null object reference

How can I check if polyline has any points assigned to it when the Activity first loads?

Answer 1

Removing all entries from your "coordList" and calling polyline.remove() on your PolyLine object or mMap.clear() to remove all markings before adding new LatLng values to your list of coordinates.

Make these class variables:

PolyLine mPolyline;
ArrayList<LatLng> mCoordList = new ArrayList<LatLng>();
GoogleMap mMap;

Now all you have to do is add the polylines when you need to:

public void onMapReady(GoogleMap googleMap){

    mMap = googleMap;

    addPolylineToMap();
}

private void addPolylineToMap(){
    double[] receivedDataArray;
    double latitude;
    double longitude;
    // Clear the list first
    mCoordList.clear();

    for (int i = 0; i < coordinatesArray.size() - 1; i++) {
        receivedDataArray = coordinatesArray.get(i);

        latitude = receivedDataArray[0];
        longitude = receivedDataArray[1];

        mCoordList.add(new LatLng(latitude,longitude));
        Log.e(TAG, "List size = " + mCoordList.size());
    }

    //You can also call ...
    //mMap.clear();
    //...in order to remove all markings on the map

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

    options = new PolylineOptions().addAll(coordList).width(10).color(Color.BLUE).geodesic(true);
    mPolyline = mMap.addPolyline(options);
}

Note: I think you could probably optimize the object coordinatesArray to be more efficient.