如何计算查询/DataSnapshot？[副本]

Question

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);

        this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
        setContentView(R.layout.activity_start);

        Button run = findViewById(R.id.button2);
        run.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(StartActivity.this, MainActivity.class);
                startActivity(intent);
            }
        });

        FirebaseApp.initializeApp(this);

        watcher = findViewById(R.id.textView3);
        player = findViewById(R.id.textView4);

        onlineCount();
    }

public void onlineCount(){
        //watcher
        refwatcher = FirebaseDatabase.getInstance()
                .getReference("online_list")
                .child("watcher")
                .child(Objects.requireNonNull(FirebaseAuth.getInstance().getCurrentUser()).getUid()).child("online");

        Query query = refwatcher.orderByChild("online").equalTo(true);


        refwatcher.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                wcount = (int) dataSnapshot.getChildrenCount();

                watcher.setText(getString(wcount) + getText(R.string._29_349_watchers_online));


            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });

        //player
        DatabaseReference refplayer = FirebaseDatabase.getInstance().getReference("online_list").child("player");

        refplayer.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                player.setText("1" + getText(R.string._230_player_online));
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });
    }

下面是我的调试代码：

   Caused by: java.lang.NullPointerException
        at java.util.Objects.requireNonNull(Objects.java:203)
        at com.bbinktattoo.nerve.StartActivity.onlineCount(StartActivity.java:65)
        at com.bbinktattoo.nerve.StartActivity.onCreate(StartActivity.java:57)
        at android.app.Activity.performCreate(Activity.java:7326)
        at android.app.Activity.performCreate(Activity.java:7317)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)