Question

我想在下图中获取sender_uid值：

这是我的以下代码。我没有任何价值，也不知道为什么。有人可以解释代码有什么问题吗？谢谢！

编辑：我只希望每个父母的最后 sender_uid -例如：

391rfBEXjVUplEW8aoahMtluSmz1_6dTv7oHnWOh55XzRuf9ouZFZkGt2

我只需要 LJxvDjdetWz1-DAFVCy 中的 sender_uid ， LJxvA65WA7MX8aaX5nF 中的否。

mDatabase.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            List<UsersListGetter> usersList = new ArrayList<>();
            recyclerView.setAdapter(new UsersListAdapter(usersList, getApplicationContext()));

            recyclerView.setAdapter(new UsersListAdapter(null, getApplicationContext()));

            for (DataSnapshot ch : dataSnapshot.getChildren()) {
                String senderReceiver[] = ch.getKey().split("_");

                if (senderReceiver[0].equals(mAuth.getUid()) || senderReceiver[1].equals(mAuth.getUid())) {
                    Query lastQuery = mDatabase.child(ch.getKey()).orderByKey().limitToLast(1);
                    lastQuery.addListenerForSingleValueEvent(new ValueEventListener() {
                        @Override
                        public void onDataChange(DataSnapshot dataSnapshot) {
                            String message = dataSnapshot.child("message_body").getValue().toString();
                            Log.d("MSG", message);
                        }

                        @Override
                        public void onCancelled(DatabaseError databaseError) {
                            //Handle possible errors.
                        }
                    });
                }
            }
        }

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

    }
});

Answer 1

您可以通过这种方式从每个节点获取sender_uid

首先创建一个pojo类以获取所需数据

public class UserPojo {

    private String sender_uid;

    public UserPojo() {

    }

    public String getSender_uid() {
        return sender_uid;
    }

    public void setSender_uid(String sender_uid) {
        this.sender_uid = sender_uid;
    }
}

，然后为每个聊天参考取回它

mDatabase.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                List<UsersListGetter> usersList = new ArrayList<>();
                recyclerView.setAdapter(new UsersListAdapter(usersList, getApplicationContext()));

                recyclerView.setAdapter(new UsersListAdapter(null, getApplicationContext()));

                for (DataSnapshot ch : dataSnapshot.getChildren()) {
                  UserPojo up = ch.getValue(UserPojo.class);
                  String senderUid = up.getSender_uid(); //here you got your sender_uid

                        Query lastQuery = mDatabase.child(ch.getKey()).orderByKey().limitToLast(1);
                        lastQuery.addListenerForSingleValueEvent(new ValueEventListener() {
                            @Override
                            public void onDataChange(DataSnapshot dataSnapshot) {
                                String message = dataSnapshot.child("message_body").getValue().toString();
                                Log.d("MSG", message);
                            }

                            @Override
                            public void onCancelled(DatabaseError databaseError) {
                                //Handle possible errors.
                            }
                        });

                }
            }

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

        }
    });

Answer 2

假设chat节点是Firebase根目录的直接子节点，要解决此问题，请使用以下查询：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
Query query = rootRef
    .child("chat")
    .child(receiver_id + "_" + sender_uid)
    .orderByChild("sender_uid")
    .limitToLast(1);
query.addListenerForSingleValueEvent(/* ... */);

使用Firebase数据库获取每个孩子的最后一个孩子

2 个答案: