在Firebase中获取子计数 [英] Getting child count in Firebase

问题描述

请问我如何简单地从Firebase查询中获取子计数.例如，假设我使用一个有10个孩子的数据库查询，我如何获得该值，因为我尝试使用 onChildChanged 并从快照中获取该值，但它没有做得好.这是因为首先它会获取数字，然后因为必须不断同步而再次查询，但是由于在第二次查询中没有实际的子项更改，因此它将返回一个零值(它将替换原始的正确值). :/

Please how do I simply get the child count from a firebase Query. For example Let's say I use a database query with 10 children, how do I get that value because I tried using onChildChanged and getting the value from the snapshot, but it does not work well. This is because at first it will get the number, then it will query again because it has to continuously sync, but because there is not actual child change at the second query it return a value if zero which will replace the original correct value. :/

   databaseReference.child("PrinterView").child(uni).child(phone).orderByChild("done").equalTo("No").addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            Toast.makeText(getActivity(),"Number:"+String.valueOf(dataSnapshot.getChildrenCount()),Toast.LENGTH_LONG).show();

        }

        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {

        }

        @Override
        public void onChildMoved(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

两者都不起作用

   databaseReference.child("PrinterView").child(uni).child(phone).orderByChild("done").equalTo("No").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            Toast.makeText(getActivity(),"Number:"+String.valueOf(dataSnapshot.getChildrenCount()),Toast.LENGTH_LONG).show();
            Vendor_view_Home_fragment.printIndicator.setText(String.valueOf(dataSnapshot.getChildrenCount()));
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

推荐答案

假定PrinterView是Firebase根目录的直接子级，请使用以下代码:

Assuming that PrinterView is a direct child of your Firebase root, please use the following code:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference yourRef = rootRef.child("PrinterView").child("Covenant University").child("588");
Query query = yourRef.orderByChild("done").equalTo("No");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        long count = dataSnapshot.getChildrenCount();
        Log.d("TAG", String.valueOf(count));
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
query.addListenerForSingleValueEvent(eventListener);

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