Question

我想查询orderByValue它总是返回null 但是当我正常删除.orderByValue数据时。请帮忙

DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference();
    mDatabase.child("newfeed").child(FirebaseRef.mAuth.getCurrentUser().getUid()).orderByValue().limitToFirst(10).addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if(dataSnapshot.exists()){
                for (DataSnapshot data : dataSnapshot.getChildren()) {
                    lastRating = data.getValue(Double.class);
                    loadData(data.getKey());
                    Log.d("Key ", data.getKey());
                }
            }
            else{
                mProgressBar.setVisibility(RecyclerView.GONE);
                mProgressBarTop.setVisibility(RecyclerView.GONE);

            }
        }
        @Override public void onCancelled(DatabaseError databaseError) {
            mProgressBar.setVisibility(RecyclerView.GONE);
        }
    });
}

以下是我的JSON示例。

"newfeed" : {
"7gE2qiqoblSHDHubiEW0IzrhzIQ2" : {
  "-Kn090eIxMH338xIwA8J" : 69259.23018812927,
  "-Kn092jf25h2Qdmk--RX" : 69268.71984827428,
  "-Kn093LPOBCCE1-Ygx6t" : 69270.82899176712,
  "-Kn093P2PE2rIml4XyKI" : 121518.05765189118,
  "-Kn09lD0cGUhRQPbvJtS" : 69394.93008559482,
  "-Kn0BYI-7IQzkCmBH8gN" : 69892.8262113143,
  "-Kn4UkNCe1rhpiJ_Rrew" : 3133576.6418433865
}

Answer 1

我不确定你会得到什么，这就是我自己运行此代码的原因：

ref.orderByValue().limitToFirst(10).addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot data : dataSnapshot.getChildren()) {
            Log.d("Key ", data.getKey()+": "+data.getValue());
        }
    }
    @Override public void onCancelled(DatabaseError databaseError) {
        throw databaseError.toException();
    }
});

打印：

D / Key：-Kn090eIxMH338xIwA8J：69259.23018812927

D / Key：-Kn092jf25h2Qdmk - RX：69268.71984827428

D / Key：-Kn093LPOBCCE1-Ygx6t：69270.82899176712

D / Key：-Kn09lD0cGUhRQPbvJtS：69394.93008559482

D / Key：-Kn0BYI-7IQzkCmBH8gN：69892.8262113143

D / Key：-Kn093P2PE2rIml4XyKI：121518.05765189118

D / Key：-Kn4UkNCe1rhpiJ_Rrew：3133576.6418433865

从快速扫描看起来对我来说是正确的顺序。

查询firebase数据库为null

1 个答案: