使用 GeoQuery 检索数据

Question

所以，我使用了这个名为 GeoFire 的库（src：https://github.com/firebase/geofire-java）从一定距离内的用户那里获取帖子。在我的代码中，我做了一个这样的方法：

private HashMap<String, GeoLocation> getPostAroundUser(DatabaseReference rootRef) {
    final HashMap<String, GeoLocation> postHashMapLocation = new HashMap<String, GeoLocation>();
    DatabaseReference refPostGeo = rootRef.child("geo").child("posts");
    final GeoFire geoFire = new GeoFire(refPostGeo);
    GeoQuery geoQuery = geoFire.queryAtLocation(new GeoLocation(mLatitude, mLongitude), 3);
    geoQuery.addGeoQueryEventListener(new GeoQueryEventListener() {
        @Override
        public void onKeyEntered(String key, GeoLocation location) {
            Log.i(TAG, "Post with key: " + key + " was added to hash with location (lat, long): (" + location.latitude + ", " + location.longitude + ")");
            postHashMapLocation.put(key, location);
            Log.i(TAG, "number of entry after added " + postHashMapLocation.size());
        }

        @Override
        public void onKeyExited(String key) {
            Log.i(TAG, "Post with key: " + key + " was removed");
            postHashMapLocation.remove(key);
        }

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

        }

        @Override
        public void onGeoQueryReady() {
            Log.i(TAG, "number of entry onGeoQueryReady " + postHashMapLocation.size());
        }

        @Override
        public void onGeoQueryError(DatabaseError error) {

        }
    });
    Log.i(TAG, "total entry in function: " + postHashMapLocation.size()); //postHashMapLocation.size() returns 0
    return postHashMapLocation;
}

但是这个方法返回的是一个空的HashMap，所以我加了一些日志看看是怎么回事，下面是日志：

02-21 18:09:32.609 15115-15115/com.example.company.app I/ExampleActivity: total entry in function: 0
02-21 18:09:32.839 15115-15115/com.example.company.app I/ExampleActivity: Post with key: -Kd7DPzEZHSdGHqfbmna was added to hash with location (lat, long): (-6.1459048, 106.692038)
02-21 18:09:32.839 15115-15115/com.example.company.app I/ExampleActivity: number of entry after added 1
02-21 18:09:32.839 15115-15115/com.example.company.app I/ExampleActivity: Post with key: -Kd7DULwW01S9-haorm9 was added to hash with location (lat, long): (-6.1459048, 106.692038)
02-21 18:09:32.839 15115-15115/com.example.company.app I/ExampleActivity: number of entry after added 2
02-21 18:09:32.839 15115-15115/com.example.company.app I/ExampleActivity: Post with key: -Kd7Dt6uvs50qddJHxiA was added to hash with location (lat, long): (-6.1459048, 106.692038)
02-21 18:09:32.839 15115-15115/com.example.company.app I/ExampleActivity: number of entry after added 3
02-21 18:09:32.839 15115-15115/com.example.company.app I/ExampleActivity: Post with key: -Kd7EOF41MijwSfrxpX1 was added to hash with location (lat, long): (-6.1459048, 106.692038)
02-21 18:09:32.839 15115-15115/com.example.company.app I/ExampleActivity: number of entry after added 4
02-21 18:09:32.849 15115-15115/com.example.company.app I/ExampleActivity: Post with key: -KdB3mJvB0K6nSCtNnoL was added to hash with location (lat, long): (-6.1333898, 106.6861029)
02-21 18:09:32.849 15115-15115/com.example.company.app I/ExampleActivity: number of entry after added 5
02-21 18:09:32.849 15115-15115/com.example.company.app I/ExampleActivity: Post with key: -KdB3r13H7y3jiovlLdi was added to hash with location (lat, long): (-6.1333898, 106.6861029)
02-21 18:09:32.849 15115-15115/com.example.company.app I/ExampleActivity: number of entry after added 6
02-21 18:09:32.849 15115-15115/com.example.company.app I/ExampleActivity: Post with key: -KdB58ArIOFKHrfEnYpr was added to hash with location (lat, long): (-6.1335054, 106.6910521)
02-21 18:09:32.849 15115-15115/com.example.company.app I/ExampleActivity: number of entry after added 7
02-21 18:09:32.869 15115-15115/com.example.company.app I/ExampleActivity: number of entry onGeoQueryReady 7

原来我在返回HashMap 之前放置的日志在geoQuery 中的日志之前触发。这就是为什么该方法返回一个空的HashMap

所以，我的问题是，如何从 onKeyEntered 中获取 HashMap 以通过此方法返回？因为从日志中可以看到，HashMap 已在 onKeyPressed 内部更新，但我无法将其检索到 geoQuery 外部。

注意：我在这里Error performing functions inside a GeoFire and Firebase query发现了类似的问题，但是没有答案。

Answer 1

Geofire 回调（例如onKeyEntered）是异步调用的……很可能在您从getPostAroundUser 方法返回之后。您需要相应地构建您的应用程序。

Answer 2

您的 hashmap 为空的原因是因为您已将其设置为最终变量，因此将其初始化为空集。 final 意味着它是不可变的，因此不能改变。所以当你初始化它时，它是空的，因此将保持为空