如何将用户的 ArrayList 存储在 Android 的 Firebase 数据库中？

Posted 2023-05-07

【中文标题】如何将用户的 ArrayList 存储在 Android 的 Firebase 数据库中？

【英文标题】：How do i store an ArrayList of users in a Firebase Database in Android?

【发布时间】：2018-09-13 19:01:06

【问题描述】：

我正在尝试制作一个拥有大量用户的应用程序。我想到的是大厅的模型，它的属性之一是用户的 ArrayList。但从我目前阅读的内容来看，说起来容易做起来难。这就是我目前所拥有的......

Lobby.class（大厅模型）

@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火力基地的地方

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();

当我运行我的代码时，会出现一个错误，指出我的 Lobby.class 文件中的 getTotalMembers() 函数正在返回一个空指针异常。数组不存储

【问题讨论】：

为什么你目前没有工作的代码？你有任何错误吗？还是您遇到了意想不到的行为？

你能详细说明你的问题吗？

或者在你运行你的代码之后有什么更新，更详细的？

请添加您的数据库结构并说明您想要实现的目标。

@DeepPatel 已编辑

【参考方案1】：

尝试一次替换此函数，然后告诉我会发生什么：

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();

【讨论】：

用什么替换函数？

在您的代码中使用相同的功能，我更改了位置： lobbyMembers.add(user); // 您在调用构造函数后将用户添加到数组中

谢谢伙计！编码愉快！

您好！我知道这听起来很奇怪，但是如果我要求您支持原始问题，可以吗？ :D 恐怕我问了太多问题，谁的分数从来没有超过 0，我很遗憾地用完了。

不用担心！有时要求支持是可以的，但不要每次都这样做。否则您将在版主审核中失去积分。 :P