java - Firebase Recyclerview 不显示数据

Question

我正在尝试从数据库中获取数据以显示在 RecyclerView 中。然而，它似乎不起作用。我的代码确实成功填充了正确数量的行项目，但未检索到数据。

Activity :

    public class Chat extends AppCompatActivity {

    String username;
    public RecyclerView recyclerView;
    private DatabaseReference databaseReference;
    Context context;

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

        context = this;

        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("Title");

// Set up the input
        final EditText input = new EditText(this);
// Specify the type of input expected; this, for example, sets the input as a password, and will mask the text
        input.setInputType(InputType.TYPE_CLASS_TEXT | InputType.TYPE_TEXT_VARIATION_PASSWORD);
        builder.setView(input);

// Set up the buttons
        builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                username = input.getText().toString();
            }
        });
        builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.cancel();
            }
        });

        builder.show();

        String key = getIntent().getStringExtra("Key");
        Toast.makeText(this, key, Toast.LENGTH_LONG).show();

        FirebaseDatabase database = FirebaseDatabase.getInstance();
        final DatabaseReference roomRef = database.getReference("rooms/" + key);
        databaseReference = database.getReference("rooms").child(key);

        ImageButton sendText = findViewById(R.id.send);

        final EditText msg = findViewById(R.id.msg);

        sendText.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                DatabaseReference roomRef2 = roomRef.child(String.valueOf(System.currentTimeMillis()));

                Map<String, String> strings = new HashMap<>();
                strings.put("user", username);
                strings.put("msg", msg.getText().toString());
                roomRef2.setValue(strings);
            }
        });

        //RECYCLER VIEW
        recyclerView = findViewById(R.id.recycler);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));

        FirebaseRecyclerAdapter<Msg,MsgViewHolder> adapter = new FirebaseRecyclerAdapter<Msg, MsgViewHolder>(
                Msg.class, R.layout.row, MsgViewHolder.class,databaseReference
        ) {
            @Override
            protected void populateViewHolder(MsgViewHolder viewHolder, Msg model, int position) {
                viewHolder.setUser(model.getUsername());
                viewHolder.setMsg(model.getMessage());
                Toast.makeText(context, model.getUsername(), Toast.LENGTH_LONG).show();
            }
        };

        recyclerView.setAdapter(adapter);
    }

    public static class MsgViewHolder extends RecyclerView.ViewHolder {
        TextView username, msg_;
        public MsgViewHolder(View itemView) {
            super(itemView);

            username = itemView.findViewById(R.id.userTxt);
            msg_ = itemView.findViewById(R.id.msgTxt);
        }

        public void setUser(String username) {
            this.username.setText(username);

        }

        public void setMsg(String message) {
            this.msg_.setText(message);
        }
    }

}

型号:

public class Msg {

    public Msg(){

    }
    public Msg(String user, String msg) {
        this.user = user;
        this.msg = msg;
    }

    private String user, msg;

    public String getMessage() {
        return msg;
    }

    public void setMessage(String message) {
        this.msg = message;
    }

    public String getUsername() {
        return user;
    }

    public void setUsername(String username) {
        this.user = username;
    }
}

再次，显然有些东西正在工作，因为 RecyclerView 填充了正确数量的行项目。但是，没有检索到任何数据。当尝试获取用户名时，toast 返回 null。

非常感谢任何帮助，谢谢。

Answer 1

在模型类中，您更改了 getter 和 setter 默认(生成)名称，Firebase 使用它们来序列化/反序列化对象。所以你的模型应该是:

public class Msg {

    public Msg(){

    }
    public Msg(String user, String msg) {
        this.user = user;
        this.msg = msg;
    }

    private String user, msg;

    public String getMsg() {
        return msg;
    }

    public void setMsg(String message) {
        this.msg = message;
    }

    public String getUser() {
        return user;
    }

    public void setUser(String username) {
        this.user = username;
    }
}

通过使用 setUsername (和其他变体)，firebase 将尝试查找名为 username 的属性，但找不到它，与 message< 相同。这就是为什么你有正确数量的对象(Firebase 能够初始化你的对象，因为你正确地提供了一个空的构造函数)，但它们里面没有任何东西(属性为 null)，因为 setter 和 getter 没有匹配属性名称。

您的属性是 user 和 msg，因此 setter 和 getter 应该反射(reflect)这一点:setUser、getUser ，setMsg，getMsg。