小编fbm*_*tma的帖子

我正在开发一个Android应用程序,其中我使用firebase作为数据库,但是当在onDataChange方法中获取变量并将它们分配给全局变量时,我得到了空变量,但是当我在onDataChange方法中调用这些变量时,它们是不是空的.

public class PositionateMarkerTask extends AsyncTask {
    public ArrayList<Location> arrayList= new ArrayList<>();
    public void connect() {
        //setting connexion parameter
        final Firebase ref = new Firebase("https://test.firebaseio.com/test");
        Query query = ref.orderByChild("longitude");

        //get the data from the DB
        query.addListenerForSingleValueEvent(new ValueEventListener() {

            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                //checking if the user exist
                if(dataSnapshot.exists()){
                    for (DataSnapshot userSnapshot : dataSnapshot.getChildren()) {
                        //get each user which has the target username
                        Location location =userSnapshot.getValue(Location.class);
                            arrayList.add(location);
                        //if the password is true , the data will be storaged in …