java - How to constantly detect nearby marker locations from current location in Google Maps android?

Question

I am trying to display a TextView at the top left corner of Google Maps that inform users if they are x distances from particular marker point locations, i.e. "You are close to location A", but only display the TextView if within range. If they move out of range, the TextView will disappear.

I understand that the Google Places API shows you all the nearby locations, but I only want to show nearby locations of the markers I have on the map if users are x distances close to them.

How can I achieve this? Would I still need to use Google Places API?

my class .java:

private GoogleMap mMap;

private LatLng currLocation;

private static final LatLng POINTA = new LatLng(32.820193, -117.232568);
private static final LatLng POINTB = new LatLng(32.829129, -117.232204);
private static final LatLng POINTC = new LatLng(32.821114, -117.231534);
private static final LatLng POINTD = new LatLng(32.825157, -117.232003);

// Array to store hotspot coordinates
private ArrayList<LatLng> markerCoords = new ArrayList<LatLng>();
private static final int POINTS = 4;

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_map);

    setUpMapIfNeeded();
}

@Override
public boolean onCreateOptionsMenu(Menu menu)
{
    // Create MenuInflater object to insert ActionBar buttons
    MenuInflater inflater = getMenuInflater();

    // Display the ActionBar buttons from .xml
    inflater.inflate(R.menu.menu_map, menu);

    return true;
}

@Override
protected void onResume()
{
    super.onResume();
    setUpMapIfNeeded();

}

private void setUpMapIfNeeded()
{
    if (mMap == null)
    {
        mMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map))
                .getMap();

        // Check if we were successful in obtaining the map.
        if (mMap != null)
        {
            markerCoords.add(POINTA);
            markerCoords.add(POINTB);
            markerCoords.add(POINTC);
            markerCoords.add(POINTD);

            setUpMap();
        }
    }
}
private void setUpMap()
{
    // Set My Location blue dot
    mMap.setMyLocationEnabled(true);

    LocationManager locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
    Criteria criteria = new Criteria();
    String provider = locationManager.getBestProvider(criteria, true);
    Location myLocation = locationManager.getLastKnownLocation(provider);

    if (myLocation != null)
    {
        double latitude = myLocation.getLatitude();
        double longitude = myLocation.getLongitude();
        currLocation = new LatLng(latitude, longitude);
    }

    for (int i = 0; i < POINTS; i++)
    {
        mMap.addMarker(new MarkerOptions()
                .position(markerCoords.get(i))
                .icon(BitmapDescriptorFactory.fromResource(R.drawable.post_it_marker)));
    }
}

map.xml

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <fragment
        xmlns:map="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/map"
        android:name="com.google.android.gms.maps.SupportMapFragment"
        map:cameraTargetLat="32.881416"
        map:cameraTargetLng="-117.237428"
        map:cameraZoom="15"
        map:mapType="normal" />
</RelativeLayout>

Can someone point me in the right direction? Thanks

Answer 1

Short answer location.distanceTo(anotherLocation)

In setupMap i recommend to add additional listener, to get all location changes in a simple way.

mMap.setMyLocationEnabled(true);
mMap.setOnMyLocationChangeListener(this);

Then in this listener you just take distance between current location and your targets. Distance in meters.

@Override
public void onMyLocationChange(Location location) {
    Location target = new Location("target");
    for(LatLng point : new LatLng[]{POINTA, POINTB, POINTC, POINTD}) {
        target.setLatitude(point.latitude);
        target.setLongitude(point.longitude);
        if(location.distanceTo(target) < METERS_100) {
            // bingo!
        }
    }
}

Of course, you should make your activity implements GoogleMap.OnMyLocationChangeListener