Firebase 在哪里调用 addChildEventListener 以便我可以节省带宽？

Question

使用我的测试 android 应用程序，我试图计算如果我的用户每 10 秒或 1 分钟添加一个孩子并与 5 台设备同步将需要多少带宽。

我的应用用户每分钟都会创建数据，因此我必须计算每个用户每月的订阅费用。每个用户每月消耗的大约带宽。

我在 MainActivity 中调用 addChildEventListener 并每 10 秒从 BroadcastReceiver 类添加子项。

• 每次我重新启动应用程序时，它都会下载所有行，这意味着消耗带宽。

• 如何减少带宽使用，让应用每次重启时只检索新添加的子项？

• 如果我添加 Firebase.getDefaultConfig().setPersistenceEnabled(true);并且用户在线还在 addChildEventListener 下载所有数据，是从服务器下载的还是本地同步的数据？

这就是我正在尝试的。

MainActivity.java

public class MainActivity extends AppCompatActivity {

Button start, stop;
TextView status;
String url = "https://<my-app>.firebaseio.com/data";
Firebase mFirebaseRef;
AlarmManager alarmManager;
PendingIntent pendingIntent;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Firebase.setAndroidContext(this);
    mFirebaseRef.getDefaultConfig().setPersistenceEnabled(true);
    alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
    start = (Button) findViewById(R.id.Start);
    stop = (Button) findViewById(R.id.stop);
    status = (TextView) findViewById(R.id.serviceText);
    mFirebaseRef = new Firebase(url);



    mFirebaseRef.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            Log.d("Data onChildAdded", dataSnapshot.getValue().toString());
            //Toast.makeText(getBaseContext(), "data=" + dataSnapshot.getValue(), Toast.LENGTH_LONG).show();
        }

        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {
            Log.d("Data onChildChanged", dataSnapshot.getValue().toString());
            //Toast.makeText(getBaseContext(), "data=" + dataSnapshot.getValue(), Toast.LENGTH_LONG).show();
        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {
            Log.d("Data onChildRemoved", dataSnapshot.getValue().toString());
            //Toast.makeText(getBaseContext(), "data=" + dataSnapshot.getValue(), Toast.LENGTH_LONG).show();

        }

        @Override
        public void onChildMoved(DataSnapshot dataSnapshot, String s) {
            Log.d("Data onChildMoved", dataSnapshot.getValue().toString());
            //Toast.makeText(getBaseContext(), "data=" + dataSnapshot.getValue(), Toast.LENGTH_LONG).show();

        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {


        }
    });

    start.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            status.setText("Started..");
            Intent myIntent = new Intent(getApplicationContext(), MyServiceReceiver.class);
            PendingIntent pendingIntent = PendingIntent.getBroadcast(getApplicationContext(), 0, myIntent, 0);
            alarmManager.setRepeating(AlarmManager.RTC_WAKEUP,System.currentTimeMillis(),10000,
                    pendingIntent);
        }
    });

    stop.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            status.setText("Stopped");
            AlarmManager alarmManager=(AlarmManager)getSystemService(Context.ALARM_SERVICE);
            Intent intent = new Intent(getApplicationContext(), MyServiceReceiver.class);
            PendingIntent pendingIntent = PendingIntent.getBroadcast(getApplicationContext(), 0, intent, 0);
            alarmManager.cancel(pendingIntent);
        }
    });
}

@Override
protected void onStop() {
    super.onStop();

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}
}

BroadcastReceiver.java

 public class MyServiceReceiver extends BroadcastReceiver {

Firebase mFirebaseRef;
Firebase mFirebaseRef2;
String url = "https://<my-app>.firebaseio.com/data";
Context context=null;
String data = "With Firebase queries, we can selectively retrieve data based on various factors. To construct a query, you start by specifying how you want your data to be ordered using one of the ordering functions: orderByChild(), orderByKey(), orderByValue(), or orderByPriority()";

@Override
public void onReceive(final Context context, Intent intent) {
    this.context = context;
    Firebase.setAndroidContext(context);
    mFirebaseRef = new Firebase(url);
    Firebase ref = mFirebaseRef.child(System.currentTimeMillis()+"");
    ref.setValue(new RecordingModel("Meeting","https://www.stadd.com",data));
    Log.d("caught", "data saved");

}
}

Answer 1

我怎样才能……每次重启应用时只检索新添加的孩子？

您可以使用Firebase Queries 来限制侦听器下载的数据。因此，您无需将 ChildEventListener 直接附加到 Firebase 位置，而是将您收到的最后一个孩子的密钥存储在某处（例如 SharedPreferences），然后下次仅从该孩子开始加载。

这是监控最后一项的key的快捷方式：

String lastChildKey;
mFirebaseRef.orderByKey().limitToLast(1).addChildEventListener(new ChildEventListener() { 
    public void onChildAdded(DataSnapshot snapshot, String s) {
        lastChildKey = snapshot.getKey();
    }
})

有了这些知识，您可以从应用重新启动时最后看到的项目开始：

Query newItems = mFirebaseRef.orderByKey().startAt(lastChildKey);
newItems.addChildEventListener(...

使用这种方法，您必须管理自己的客户端状态，因为您实际上是在用自己的策略替换 Firebase 的客户端缓存/同步策略。