如何在Android中从Google Map v2清除圆圈和标记

Question

I am trying to draw a circle on the Google Map v2 in android with center as the current location as soon as the location gets changed. Now what I am seeing is, everytime when the location gets changed, circle keeps getting drawn(overlapping each other if the location is same) without deleting the previous circle. And same thing is happening with the Marker as well.

Below is the code I am using to draw the circle on the Google Map v2

@Override
public void onLocationChanged(Location location) {
    if (location != null) {

    // Create a LatLng object for the current location
    LatLng latLng = new LatLng(location.getLatitude(), location.getLongitude());

    // Show the current location in Google Map
    map.moveCamera(CameraUpdateFactory.newLatLng(latLng));

    // Zoom in the Google Map
    map.animateCamera(CameraUpdateFactory.zoomTo(14));

    CircleOptions circleOptions = new CircleOptions().center(latLng) // set center
    .radius(1000) // set radius in meters
    .fillColor(Color.TRANSPARENT) // default
    .strokeColor(0x10000000).strokeWidth(5);

    myCircle = map.addCircle(circleOptions);

    map.addMarker(new MarkerOptions().position(latLng).title("You are here!"));
}

How do I make sure, that whenever the circle is getting drawn next time, previous circle and marker is cleared from the Google Map. What changes I need to make in my code?

Any help will be appreciated.

Answer 1

Removing things from the map is simple. For whatever reason, in GoogleMaps v2 you cannot simply remove a Marker by getting its id since that value is generated automatically on creation and thus pretty much useless. To work around this, all you need to do is create something that can store a reference to the object you want to remove. One way to do this is to create HashMap and store a reference to your Marker , circle, or anything else you want the ability to remove, with some unique id. By storing a reference to things you place on the map in a HashMap however you can then call remove on the marker associated with that key each time your location updates. The same goes for the circle (though you will need a different HashMap if you set the types as I have below - I don't know if you can use a generic String, Object map that will store both).

To use this method, declare your HashMap like its an instance variable so it can be accessed from all the methods within your Activity

private HashMap<String, Marker> mapStuff = new HashMap<String, Marker>();

Then wherever you create your Marker or other map objects, just add them to the HashMap with some key value

Marker dude = map.addMarker(new MarkerOptions()
.position(newLatLng(latitude, longitude))
.title(MARKER_TITLE)
.snippet(SNIPPET));
mapStuff.put("userMarker", dude);

The concept is really the same as what was suggested by another poster, which is just to have a Marker as an instance variable and store a reference there. Both do the same thing. The HashMap approach works best if you're dealing with multiple markers or objects. If you're only dealing with one Marker or one circle, the single variable approach is probably more correct since you do not need to use a Collection to add or remove one marker. Just declare

private Marker userMarker;

and then where you add the Marker to the map, store a reference

userMarker = map.addMarker(new MarkerOptions()
.position(newLatLng(latitude, longitude))
.title(MARKER_TITLE)
.snippet(SNIPPET));

When you update your location, probably in onLocationChanged just check for the existance of the marker and remove it if present and re-add

if(userMarker == null){
    displayUserMarker(location);
} else {
    userMarker.remove;
    displayUserMarker(location);
}

Answer 2

map.clear();

add this before if (location != null)

So that every time the location changes all the markers and circle is removed and drawn again

Answer 3

First of all, keep a reference to marker just like you keep to circle

myMarker = map.addMarker(new MarkerOptions().position(latLng).title("You are here!"));

When you want to remove them, just call remove() :

myCircle.remove();
myMarker.remove();