我的项目是识别客户端是在线还是离线。我使用了 Android-Firebase 文档中提供的代码，该文档在“.info/connected”中使用了一个 EventListener。
// since I can connect from multiple devices, we store each connection instance separately
// any time that connectionsRef's value is null (i.e. has no children) I am offline
final FirebaseDatabase database = FirebaseDatabase.getInstance();
final DatabaseReference myConnectionsRef = database.getReference("users/joe/connections");
// stores the timestamp of my last disconnect (the last time I was seen online)
final DatabaseReference lastOnlineRef = database.getReference("/users/joe/lastOnline");
final DatabaseReference connectedRef = database.getReference(".info/connected");
connectedRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot snapshot) {
boolean connected = …