Android Firebase显示当前已登录的用户详细信息

我试图显示当前登录用户的详细信息。我尝试了一些方法来尝试解决此问题，但似乎返回的所有结果都是null。我的用户Firebase数据库是：

数据库

我要去哪里错了？

FirebaseAuth mAuth = FirebaseAuth.getInstance();

FirebaseAuth firebaseAuth = FirebaseAuth.getInstance();


Button mBeerButton;
Button mBeerButtonTwo;
Button mBeerButtonThree;
Button mBeerButtonFour;
Button mSignOutButton;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_home_screen);


    String mUserID = firebaseAuth.getCurrentUser().getUid();
    DatabaseReference ref= FirebaseDatabase.getInstance().getReference().child("Users");

    ref.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            String mUsername = dataSnapshot.child("mUserName").getValue().toString();
            Toast.makeText(homeScreen.this,"User name is "+ mUsername,Toast.LENGTH_SHORT).show();
        }

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

        }
    });

问题来源：Stack Overflow