如何将用户阵列存储在Android的Firebase数据库中

Question

我试图制作一个具有用户大厅的应用程序。我想到的是大堂拥有和模型，其属性之一将是用户的数组列表。但是，从到目前为止，我的阅读内容是说起来容易做起来难的。这就是我到目前为止的……

Lobby.Class(Lobby Model(

@Parcel
public class Lobby {
    private String owner;
    private String location;
    private double cost;
    private String startDate;
    private ArrayList<FirebaseUser> members;
    public Lobby(){
    }
    public Lobby(String owner, String location, double cost, String startDate, ArrayList<FirebaseUser> members) {
        this.owner = owner;
        this.location = location;
        this.cost = cost;
        this.startDate = startDate;
        this.members = members;
    }
    public String getOwner() {
        return owner;
    }
    public void setOwner(String owner) {
        this.owner = owner;
    }
    public String getLocation() {
        return location;
    }
    public void setLocation(String location) {
        this.location = location;
    }
    public double getCost() {
        return cost;
    }
    public void setCost(double cost) {
        this.cost = cost;
    }
    public String getStartDate() {
        return startDate;
    }
    public void setStartDate(String startDate) {
        this.startDate = startDate;
    }
    public ArrayList<FirebaseUser> getMembers() {
        return members;
    }
    public void setMembers(ArrayList<FirebaseUser> members) {
        this.members = members;
    }
    public String getDateText(){
        String dateString = DateFormat.getDateInstance().format(new Date());
        return dateString;
    }
    public int getTotalMembers(){
        return members.size();
    }
}

这是我将大厅保存到Firebase

的地方

public class createLobby extends AppCompatActivity {
private static String TAG = "CreateLobby";
private TextView displayDate;
private DatePickerDialog.OnDateSetListener dateListener;
private EditText locIn, costIn;
private FirebaseAuth firebaseAuth;
private DatabaseReference databaseReference;
private DatabaseReference usernameGet;
private Button submitLobbyButton;
private String ownerName;
FirebaseUser user;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_create_lobby);
    firebaseAuth = FirebaseAuth.getInstance();
    user = firebaseAuth.getCurrentUser();
    databaseReference = FirebaseDatabase.getInstance().getReference();
    usernameGet = databaseReference.child(user.getUid()).child("userName");
    usernameGet.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            ownerName = dataSnapshot.getValue(String.class);
            Log.v("Username", ownerName);
        }
        @Override
        public void onCancelled(DatabaseError databaseError) {
        }
    });
    locIn = (EditText)findViewById(R.id.loc_input);
    costIn = (EditText)findViewById(R.id.cost_input);
    displayDate = (TextView)findViewById(R.id.date_picker);
    displayDate.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Calendar cal = Calendar.getInstance();
            int year = cal.get(Calendar.YEAR);
            int month = cal.get(Calendar.MONTH);
            int day = cal.get(Calendar.DAY_OF_MONTH);
            DatePickerDialog dialog = new DatePickerDialog(
                    createLobby.this, android.R.style.Theme_Holo_Light_Dialog_MinWidth,
                    dateListener, year, month, day);
            dialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
            dialog.show();
        }
    });
    dateListener = new DatePickerDialog.OnDateSetListener() {
        @Override
        public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
            month = month+1;
            String date = month + "/" + dayOfMonth + "/" + year;
            displayDate.setText(date);
        }
    };
    submitLobbyButton = (Button)findViewById(R.id.create_lobby_button);
    submitLobbyButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            submitLobby();
        }
    });
}
public void submitLobby(){
    firebaseAuth = FirebaseAuth.getInstance();
    user = firebaseAuth.getCurrentUser();
    DatabaseReference lobbyRef = FirebaseDatabase.getInstance().getReference(Constants.LOBBIES);
    String owenerMan = ownerName;
    String gameLoc = locIn.getText().toString();
    Double gameCost = Double.parseDouble(costIn.getText().toString());
    String gameDate = displayDate.getText().toString();
    ArrayList<FirebaseUser> lobbyMembers = new ArrayList<>();
    Lobby newLobby = new Lobby(owenerMan, gameLoc, gameCost, gameDate, lobbyMembers);
    lobbyMembers.add(user);
    lobbyRef.push().setValue(newLobby);
    Log.v("creator", owenerMan);
    Log.v("newLobby", newLobby.getStartDate());
    Toast.makeText(getApplicationContext(), "Lobby Added!", Toast.LENGTH_SHORT).show();
}
}

当我运行代码时，出现错误，说我的lobby.class文件中的getTotalMembers((函数正在返回null指针异常。数组不存储

Answer 1

尝试替换此功能后，让我知道，发生了什么：

public void submitLobby(){
    firebaseAuth = FirebaseAuth.getInstance();
    user = firebaseAuth.getCurrentUser();
    DatabaseReference lobbyRef = FirebaseDatabase.getInstance().getReference(Constants.LOBBIES);
    String owenerMan = ownerName;
    String gameLoc = locIn.getText().toString();
    Double gameCost = Double.parseDouble(costIn.getText().toString());
    String gameDate = displayDate.getText().toString();
    ArrayList<FirebaseUser> lobbyMembers = new ArrayList<>();
    lobbyMembers.add(user);                             // You were adding user into Array after calling constructor
    Lobby newLobby = new Lobby(owenerMan, gameLoc, gameCost, gameDate, lobbyMembers);
    lobbyRef.push().setValue(newLobby);
    Log.v("creator", owenerMan);
    Log.v("newLobby", newLobby.getStartDate());
    Toast.makeText(getApplicationContext(), "Lobby Added!", Toast.LENGTH_SHORT).show();
}