android - Firebase 使用随机生成的 key 访问子项

Question

我正在尝试创建一个基本应用程序，在其中我将消息发送到 Firebase 中的实时数据库并在 ListView 中接收它们。(这是 Whatsapp 的翻版。)我发送用户的用户名和消息通过推送消息到数据库。但是，由于随机生成的 key ，我无法读取它们并从中创建 ListView 。 有没有办法接收引用聊天的所有子项并将它们放在 ListView 中？

附言。我无法使用 .getKey 函数，因为消息将来自不同的设备。

页数。 可以提供额外的代码或详细信息。

代码:

public class MessageBoard extends AppCompatActivity {
    private static final String TAG = "MessageBoard";

    private FirebaseAuth mAuth= FirebaseAuth.getInstance();
    private FirebaseDatabase database = FirebaseDatabase.getInstance();
    private FirebaseUser user = mAuth.getCurrentUser();
    private ArrayList<String> chatlist;
    private ArrayAdapter<String> arrayAdapter;
    private DatabaseReference ref;
    private DatabaseReference Users;
    private String username;
    private String email;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_message_board);

        final Button SignOut = (Button) findViewById(R.id.SignOut);
        final Button SendMessage = (Button) findViewById(R.id.SendMessage);
        final EditText MessageText = (EditText) findViewById(R.id.Message_Text);
        final ListView listView = (ListView) findViewById(R.id.Listview);
        final TextView UserNameDis = (TextView) findViewById(R.id.UserNameDisplay);
        if(user != null){
            email = user.getEmail();

        }


        chatlist = new ArrayList<String>();

        arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, chatlist);

        listView.setAdapter(arrayAdapter);

        ref = database.getReference("chat");

//-----------------------------------------------------------------------------------------------------------------------------------------
//to login screen

        if(user == null){
            startActivity(new Intent(MessageBoard.this, Login.class));
            Log.d(TAG, "Login");
        }else{
            Toast.makeText(MessageBoard.this, "Login Succesfull.",
                    Toast.LENGTH_SHORT).show();
        }




//-----------------------------------------------------------------------------------------------------------------------------------------
//to username screen
        if(user.getDisplayName() == null){
            startActivity(new Intent(MessageBoard.this, Username.class));
            Log.d(TAG, "Username");
        }else{
            Toast.makeText(MessageBoard.this, "Username Known.",
                    Toast.LENGTH_SHORT).show();
        }



//-----------------------------------------------------------------------------------------------------------------------------------------
        //set username welcome text
        username = user.getDisplayName();
        String Welcome = "Welcome " + username;
        UserNameDis.setText(Welcome);


//-----------------------------------------------------------------------------------------------------------------------------------------
//sign out button
        SignOut.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                FirebaseAuth.getInstance().signOut();
                startActivity(new Intent(MessageBoard.this,Login.class));

            }
        });



//-----------------------------------------------------------------------------------------------------------------------------------------
// chat data update
        ref.orderByKey();

        ref.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                //where I think the receiving code should be
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
//-----------------------------------------------------------------------------------------------------------------------------------------
//message send
        SendMessage.setOnClickListener(new View.OnClickListener(){
            public void onClick(View v) {
                String push = ref.push().getKey();
                ref.child(push).child("message").setValue(username);
                ref.child(push).child("username").setValue(username);

            }
        });
//-----------------------------------------------------------------------------------------------------------------------------------------
    }

}

Answer 1

从您可以获得每个随机生成的键及其值的节点检索数据。

ref.addValueEventListener(new ValueEventListener()
{
@Override
public void onDataChange(DataSnapshot dataSnapshot)
{
    HashMap<String, Object> allMessage = (HashMap<String, Object>) 
    dataSnapshot.getValue();
    String[] pushIds = allMessage.keySet().toArray(new String[0]);
    for (int j = 0; j < allMessage.size(); j++)
    {
        HashMap<String, Object> singleMessage = (HashMap) 
        allMessage.get(pushIds[j]);
        Message message = new message(singleMessage);
        allRequests.add(message);

    }
}

@Override
public void onCancelled(DatabaseError databaseError)
{

}
});

你的模型类

 public class Message
 {
    String message;
    public Message(HashMap<String,Object> singleMessage)
  {
    message = singleMessage.get("message").toString();
  }
  };