Android Firebase，获取键在节点中的位置

Question

我想根据用户的排名获取数据。首先按用户点数排序，获取用户在节点中的位置。但是我想不出实现这个的方法。

首先这是我的 firebase 'users' 节点

也许会像'databaseRef.child("users").orderByChild("points")...' 我从这里不知道。

ps。它不是第 n 个项目。这是 'where is the item'（第 n 项）

谢谢！

Answer 1

敬请阅读

The callback function receives a DataSnapshot, which is a snapshot of the data. A snapshot is a picture of the data at a particular database reference at a single point in time. Calling val() / getValue() on a snapshot returns the a language-specific object representation of the data. If no data exists at the reference's location, the snapshot's value is null.

如果你想获得所有 points 然后检查这个 LOGIC.

DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("products");
    ref.addListenerForSingleValueEvent(
            new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {

                    ArrayList<Integer> points = new ArrayList<>();
                    for (Map.Entry<String, Object> entry : products.entrySet()){
                        Map singleUser = (Map) entry.getValue();
                        points.add((Integer) singleUser.get("points"));
                    }

                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                    //handle databaseError
                }
            });

Answer 2

这可以通过在 dataSnapshot 循环中添加一个 ctr 来完成

myRef = FirebaseDatabase.getInstance().getReference().child("users");
final Query query = myRef.orderByChild("points");
query.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {

        int total = dataSnapshot.getChildrenCount();
        int i = 0;
        // loop through dataSnapshot
        for (DataSnapshot childSnapshot : dataSnapshot.getChildren()) {
            String nickName = childSnapshot.child("nickName").getValue(String.class);
            if (nickName.equals(mUser.getNickName()) {
                //when nickName would match
                int userPlace = total - i;
                int points = childSnapshot.child("points").getValue(Interger.class);

                //do something here
                break;
            } else {
                i++;
            }
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

Answer 3

我解决了这个问题。 Android_K.Doe的回答是正确的。我在他的代码中添加了一些代码。因为Firebase数据库没有给出降序查询。

final Query query = databaseReference.child("users").orderByChild("points");
        query.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                int i = 0;
                int all = (int) dataSnapshot.getChildrenCount();
                Log.d(TAG, "all: " + all);
                for (DataSnapshot ds : dataSnapshot.getChildren()) {

                    String nickName = ds.child("nickName").getValue(String.class);
                    if (nickName.equals(user.getNickName())) {
                        Log.d(TAG, "nickName: " + user.getNickName());
                        int userPlace = i;
                        Log.d(TAG, "position: " + userPlace);
                        myInfoRankingNumTxt.setText(Integer.toString(all - (i)) + "위");
                        break;
                    } else {
                        i++;
                    }
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

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