Android:Firebase花费了太多时间来获取数据

Question

我在我的应用程序中使用Firebase的实时数据库功能.数据库看起来像这样:

节点104,1040 ......具有其他元件/数据.我正在获取此数据,并按每个Integer父级中可用的节点'updatedAt'的值对其进行排序,如snap中所示.我onChildAddedListener()用来获取最后20个元素."结果"中有大约1050个节点.

问题:

1. 即使在高速WiFi上,获取数据也需要30秒左右的时间.

2. Firebase是否允许任何回调通知已提取数据？我想将每个自定义对象附加ArrayList到从Firebase收到的对象,并通过意图将其传递给另一个活动.我正在计算收到的对象,当它变为20时,我打开了我的活动.这是唯一的方法吗？如果有更好的出路,请建议.

这是我的代码:

 public class Splash extends AppCompatActivity{

        private static final String TAG = "Splash Activity";
        private ArrayList<News> NewsArrayList = new ArrayList<>();   
        private DatabaseReference newsReference;
        private int position = 0;

        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_splash);

            newsReference = FirebaseDatabase.getInstance().getReference().child("results");
            Query queryNewsReference = newsReference.orderByChild("updatedAt").limitToLast(20);
            fetchNews(queryNewsReference);
        }

        private void fetchNews(Query queryNewsReference) {

            queryNewsReference.addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                    Log.d(TAG, "onChildAdded:" + dataSnapshot.getKey());
                    News newsObject = dataSnapshot.getValue(News.class);
                    Log.d(TAG,"News Title: "+ newsObject.getVideo_title());
                    NewsArrayList.add(newsObject);
                    position++;
                    if(position == 20){
                    startMainActivity(); 
                    }
                }
                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, String s){
                    Log.d(TAG, "onChildChanged() called on key: "+ dataSnapshot.getKey());
                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {
                    Log.d(TAG, "onChildRemoved() called on key: "+ dataSnapshot.getKey());
                }

                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, String s) {
                    Log.d(TAG, "onChildMoved() called on key: "+ dataSnapshot.getKey());
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                    Log.e(TAG,"Database Error: "+databaseError.toString());
                }
            });
        }

        private void startMainActivity() {
            Intent intent = new Intent(Splash.this,MainActivity.class);
            intent.putExtra("NewsList",NewsArrayList);
            Splash.this.startActivity(intent);
        }

Answer 1

在添加值侦听器之前尝试重新连接到 firebase：

private void fetchNews(Query queryNewsReference) 
{    
    if (FirebaseDatabase.getInstance() != null)
    {
        FirebaseDatabase.getInstance().goOffline();
    }

    FirebaseDatabase.getInstance().goOnline();

    queryNewsReference.addChildEventListener(new ChildEventListener() {

    ...
}