虽然实际问题是,GeoFire已经需要知道.child(“location”),但不可能用Reference来表示;只有DataSnapshot有getChildren().

底线是：

you’d have to create a separate locations Reference,in order to avoid the nesting. nevertheless you still can use the related uid key for these nodes (or at least add it as a child-node),in order to be able to look up within the users Reference. it’s a 1:1 relation,in between two References.

所以这是一个有效的Java示例,只是因为……

我们假设以下结构(如上所述)：

{
  "locations" : {
    "CR88aa9gnDfJYYGq5ZTMwwC38C12" : {
      ".priority" : "9q8yywdgue","g" : "9q8yywdgue","l" : [ 37.7853889,-122.4056973 ]
    }
  },"users" : {
    "CR88aa9gnDfJYYGq5ZTMwwC38C12" : {
      "displayName" : "user 01",...
    }
  }
}

数据库规则应该有.indexOn用于位置字段g set：

{
  "rules": {
    ...
    "locations": {
      ".indexOn": "g"
    }
  }
}

模块的build.gradle中的依赖项：

dependencies {
    ...
    api "com.firebase:geofire-android:2.3.1"
}

这表明了如何通过GeoQuery结果获取用户的快照;

注意GeoQueryEventListener而不是GeoQueryDataEventListener：

public class GeofireActivity extends AppCompatActivity {

    private static final String LOG_TAG = GeofireActivity.class.getSimpleName();

    private DatabaseReference refBase     = null;
    private DatabaseReference refLocation = null;
    private DatabaseReference refUser     = null;

    private GeoFire geoFire = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        this.setContentView(R.layout.fragment_geofire);
        this.setReferences();
    }

    private void setReferences() {
        this.refBase = FirebaseDatabase.getInstance().getReference();
        this.refUser = refBase.child("users");
        this.refLocation = refBase.child("locations");
        this.geoFire = new GeoFire(this.refLocation);
    }

    private void searchNearby(double latitude,double longitude,double radius) {
        this.searchNearby(new GeoLocation(latitude,longitude),radius);
    }

    private void searchNearby(GeoLocation location,double radius) {

        GeoQuery geoQuery = this.geoFire.queryAtLocation(location,radius);
        geoQuery.addGeoQueryEventListener(new GeoQueryEventListener() {

            @Override
            public void onKeyEntered(String key,GeoLocation location) {

                String loc = String.valueOf(location.latitude) + "," + String.valueOf(location.longitude);
                Log.d(LOG_TAG,"onKeyEntered: " + key + " @ " + loc);

                /* once the key is known,one can lookup the associated record */
                refUser.child(key).addListenerForSingleValueEvent(new ValueEventListener() {

                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                        Log.d(LOG_TAG,"onDataChange: " + dataSnapshot.toString());
                    }

                    @Override
                    public void onCancelled(@NonNull DatabaseError firebaseError) {
                        Log.e(LOG_TAG,"onCancelled: " + firebaseError.getMessage());
                    }
                });
            }

            @Override
            public void onKeyExited(String key) {
                Log.d(LOG_TAG,"onKeyExited: " + key);
            }

            @Override
            public void onKeyMoved(String key,GeoLocation location) {
                Log.d(LOG_TAG,"onKeyMoved: " + key);
            }

            @Override
            public void onGeoQueryReady() {
                Log.d(LOG_TAG,"onGeoQueryReady");
            }

            @Override
            public void onGeoQueryError(DatabaseError error) {
                Log.e(LOG_TAG,"onGeoQueryError" + error.getMessage());
            }
        });
    }
}

为了保持完整性,在删除用户记录时,需要删除关联的位置记录 – 否则会导致密钥无法再查找.