Firebase 同步如何与共享数据一起工作?

Here is simpler code, where I tried to reproduce the error. :

MyApplication.java

public class MyApplication extends Application {
    @Override
    public void onCreate() {
        super.onCreate();
        Firebase.setAndroidContext(this);
        Firebase.getDefaultConfig().setLogLevel(Logger.Level.DEBUG);
        Firebase.getDefaultConfig().setPersistenceEnabled(true);


    }
}

MainActivity

public class MainActivity extends AppCompatActivity {

    Firebase ref;
    User user;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ref = new Firebase("https://millezim-test.firebaseIO.com").child("user");
        ref.keepSynced(true);

        Button br = (Button) findViewById(R.id.b_read);
        Button bs = (Button) findViewById(R.id.b_save);
        final TextView tv_r = (TextView) findViewById(R.id.tv_value_toread);
        final EditText tv_s = (EditText) findViewById(R.id.tv_value_tosave);

        user = new User();

        bs.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (!tv_s.getText().toString().equalsIgnoreCase(""))
                    user.setAge(Integer.valueOf(tv_s.getText().toString()));
                ref.setValue(user);
            }
        });

        br.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                ref.addListenerForSingleValueEvent(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        User u = dataSnapshot.getValue(User.class);
                        if (u != null)
                            tv_r.setText(String.valueOf(u.getAge()));
                        else
                            tv_r.setText("Bad Value");
                    }

                    @Override
                    public void onCancelled(FirebaseError firebaseError) {

                    }
                });
            }
        });

        ref.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                User u = dataSnapshot.getValue(User.class);
                u.setCounter(u.getCounter() + 1);
                user = u;
                saveUser();
            }

            @Override
            public void onCancelled(FirebaseError firebaseError) {

            }
        });
    }

    public void saveUser() {
        ref.setValue(user);
    }
}

如果您只是更改应用程序中的值，则计数器会增加直到应用程序停止:这是正常的.但什么是链子，是时代从旧到新，再到旧的循环，没有停止.

ref.addListenerForSingleValueEvent(new ValueEventListener() {...