从 Firebase 获取项目的位置

Question

I have found the code that runs trough my list of leader board and returns the corresponding value. But I would need to return the position of the item in the list. How should I modify the code so it would return the position (index) of the item.

Thanks.

//query for sorting by score
    score = FirebaseDatabase.getInstance().getReference().child("Leaders");
    final Query query = score.orderByChild("uID").equalTo(mCurrentUser.getUid());

    query.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            Iterator<DataSnapshot> iterator = dataSnapshot.getChildren().iterator();

            int length = (int) dataSnapshot.getChildrenCount();

            String[] sampleString = new String[length];

            while(i < length) {
                sampleString[i] = iterator.next().getValue().toString();
                //Log.d(Integer.toString(i), sampleString[i]);

                //print the value of current score
                Toast.makeText(LeaderBoardActivity.this,sampleString[i],Toast.LENGTH_LONG).show();
                i++;
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

Answer 1

I've edited the code based on your comments. Since you only care about the position and score...

// you will need to query the database based on scores
score = FirebaseDatabase.getInstance().getReference().child("Leaders");
final Query query = score.orderByChild("Score");
query.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        // get total leaders. Let's say total leader is 5 persons
        int total = (int) dataSnapshot.getChildrenCount();
        // let's say userB is actually 2nd in the list
        int i = 0;
        // loop through dataSnapshot
        for (DataSnapshot childSnapshot : dataSnapshot.getChildren()) {
            String uID = childSnapshot.child("uID").getValue();
            if (uID.equals(mCurrentUser.getUid()) {
                // the list is ascending, when finally reach userB, i = 3
                int userPlace = total - i;    // gives 2
                int score = childSnapshot.child("Score").getValue(Interger.class);
                break;
            } else {
                i++;
            }
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

Note that this can be very bandwidth consuming. As you get more and more users, you will need to download all the user data for each query. It might be better if you just show the top 5 leaders etc.

Answer 2

I use following method to change child value by position, hope this can give you some helps:

DataSnapshot targetData;

@Override
protected void onStart() {
    super.onStart();

    targetReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshots) {
            targetData = dataSnapshots;        //save in global variable
        }

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

private void yourMethod() {
    int index = 0;

    for (DataSnapshot childSnapshot : targetData.getChildren()) {
        if (index == 1) {        //your target index
            DatabaseReference currentReference = childSnapshot.getRef();

            currentReference.setValue("xxx");
        }

        index++;
    }
}