删除上一个标记

Question

我遇到了麻烦。我在Realtime Firebase中获取经纬度并创建了一个标记，但每次纬度和经度都有更新时，它将创建另一个标记。

如何删除上一个标记？这是我的代码：

passRef = new Firebase(Config.FIREBASE_URL_PASSENGER);
passRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot snapShot : dataSnapshot.getChildren()) {
            for (int cnt = 0; cnt <= dataSnapshot.getChildrenCount(); cnt++) {
                if (snapShot.child("latitude").exists() && snapShot.child("longitude").exists() && snapShot.child("destination").exists()) {

                    passUsername = snapShot.child("name").getValue().toString();
                    //getting the passenger's current location
                    locLatPass = Double.valueOf(snapShot.child("latitude").getValue().toString());
                    locLongPass = Double.valueOf(snapShot.child("longitude").getValue().toString());
                    latlngpass = new LatLng(locLatPass, locLongPass);

                    MarkerOptions passLocMarkerOptions = new MarkerOptions();
                    passLocMarkerOptions.position(latlngpass);
                    passLocMarkerOptions.title(passUsername+ "'s Location");

                    passLocMarkerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_BLUE));
                    passLocationMarker = mMap.addMarker(passLocMarkerOptions);
                } else {
                }
            }
            Toast.makeText(MapsActivity.this, "Passenger Username" + passUsername + " latitude" + locLatPass + "Longitude" + locLongPass, Toast.LENGTH_LONG).show();
        }
    }

    @Override
    public void onCancelled(FirebaseError firebaseError) {

    }
});

Answer 1

这将清除地图上绘制的所有现有标记：

mMap.clear();

Answer 2

您可以通过调用remove()方法删除标记。

marker.remove();

修改

如果每个孩子的价值都会发生变化，您应该考虑使用ChildEventListener

以下是您的问题的解决方案，您必须创建一个HashMap来保存标记，然后您可以删除或只修改上一个标记。

Map<String, Marker> markers = new HashMap();

Database.waypoints().addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String s) {
        passUsername = dataSnapshot.child("name").getValue().toString();
        //getting the passenger's current location
        locLatPass = Double.valueOf(dataSnapshot.child("latitude").getValue().toString());
        locLongPass = Double.valueOf(dataSnapshot.child("longitude").getValue().toString());
        latlngpass = new LatLng(locLatPass, locLongPass);

        MarkerOptions passLocMarkerOptions = new MarkerOptions();
        passLocMarkerOptions.position(latlngpass);
        passLocMarkerOptions.title(passUsername+ "'s Location");

        passLocMarkerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_BLUE));
        Marker marker = mMap.addMarker(passLocMarkerOptions);
        markers.put(dataSnapshot.getKey(), marker);
    }

    @Override
    public void onChildChanged(DataSnapshot dataSnapshot, String s) {
        passUsername = dataSnapshot.child("name").getValue().toString();
        //getting the passenger's current location
        locLatPass = Double.valueOf(dataSnapshot.child("latitude").getValue().toString());
        locLongPass = Double.valueOf(dataSnapshot.child("longitude").getValue().toString());
        latlngpass = new LatLng(locLatPass, locLongPass);

        MarkerOptions passLocMarkerOptions = new MarkerOptions();
        passLocMarkerOptions.position(latlngpass);
        passLocMarkerOptions.title(passUsername+ "'s Location");

        if (markers.contains(dataSnapshot.getKey())) {
            markers.get(dataSnapshot.getKey()).remove();
            // you can also modify the marker instead of removing it and then add it again
        }
        passLocMarkerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_BLUE));
        Marker marker = mMap.addMarker(passLocMarkerOptions);
        markers.put(dataSnapshot.getKey(), marker);
    }

    @Override
    public void onChildRemoved(DataSnapshot dataSnapshot) {

    }

    @Override
    public void onChildMoved(DataSnapshot dataSnapshot, String s) {

    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});